Personal Computer Components and Subsystems

This chapter is from the book 

Chapter Syllabus

• Hardware Components
• Software Components
• PC Boot Process

Several core components and ancillary subsystems comprise PCs. The core components provide the basic functionality of the PC. Ancillary subsystems enhance the basic functionality to support different applications, such as graphics imaging, multimedia applications, and more. PCs are a package of matched components. The components are matched for speed (somewhat tuned) to provide the best overall performance. It makes little sense to have a super fast Central Processing Unit (CPU) chip and a slow fixed disk drive or slow Random Access Memory (RAM). Such a combination produces a slow system. PCs are as fast as their most used and slowest component. Sometimes fixing PC problems is making sure that the PC components are properly matched for speed. However, the best PC is always the most reliable PC. Nerds may brag about their fast PCs, but their PCs rarely fail.

The PC core components ranked from fastest to slowest are:

• CPU chip—fastest
• RAM
• Display adapter
• Read-Only Memory (ROM)
• Fixed disk drive
• Universal Serial Bus (USB)
• Network adapter
• CD-ROM drive
• CD Rewriteable (CD-RW) drive
• Digital Versatile Disk (DVD) drive
• Floppy disk drive
• Parallel port
• Serial port
• Mouse
• Keyboard
• The nut behind the keyboard—slowest

Components and subsystems fall into three categories: hardware, software, and network. Hardware components are those components physically installed in the PC or connected to it. They are the core and ancillary subsystems examined in this chapter. Software components are covered in Chapter 9 through Chapter 16. Network connections are common components of most PC systems today.

Network connections are either dialup or Local Area Network (LAN). Cable modem and Digital Subscriber Line (DSL) connections are LAN connections as well. The network connections are attached to PC hardware components and work in conjunction with other computers and networking hardware residing somewhere on the attached network. I discuss networking as it impacts the PC hardware and software components and subsystems, but networks and external networking components are beyond the scope of this book.

Hardware Components

PC hardware is the focus of this section. PC hardware core components include the CPU chip, the ROM, the RAM, chip sets and buses, the power supply, serial and parallel Input/Output (I/O) ports, the floppy disk controller and drive, the fixed disk controller and drive, the CD-ROM drive, the DVD-ROM drive, the display adapter and monitor, the keyboard, and the mouse. See Figure 1–1. These components provide all basic PC functions. Ancillary subsystems are sound cards, LAN adapters, video cameras, and so forth.

Figure 1-1 Typical PC system.

The main PC chassis contains the central component for all PCs, the Main Logic Board (MLB). This is sometimes referred to as the system board or motherboard.

The MLB is based on a specific CPU and supporting chip set. It has a specific bus configuration and mounts the CPU, the ROM, and the RAM. Serial and parallel interfaces, as well as the keyboard interface, bus mouse interface, floppy disk controller, fixed disk Integrated Drive Electronics (IDE) controllers, and USB ports are typically built into the MLB. Proprietary systems and laptop PCs have Video Graphics Array (VGA) display controllers incorporated into the MLB as well. Other controllers are bus-connected cards inserted into the bus of the MLB.

Main Chassis

The main chassis or case is the box containing most PC components. Components may be connected to the main chassis using USB connections. The main chassis would then contain the PC's core components, and the ancillary subsystems would occupy desktop space.

The main chassis for the PC Advanced Technology (AT) contained the MLB, its installed Intel 286 CPU chip, ROM, and RAM. The supporting chip sets provided Industry Standard Architecture (ISA) 8-bit and 16-bit connectors for installing adapter cards. Adapter cards typically installed in the AT were serial and parallel I/O controllers, display adapters, and disk controllers. The typical AT style PC chassis contained the floppy drive(s) and a fixed disk. The primary user input was by a keyboard. This was the typical 1985 PC.

In the early 1990s, PCs changed. At that time, Microsoft Windows made a successful entrance into the PC marketplace. It pressured PC manufacturers to change main chassis components more rapidly than before. Similar to the 1980s PCs, most MLBs had an installed Intel 386 or 486 CPU chip—although some supported Advanced Micro Devices (AMD) CPU chips—external CPU cache RAM, ROM, and RAM. The MLB also included the serial and parallel port I/O controllers and IDE fixed disk and floppy disk controllers. The bus connections were mainly ISA 8-bit and 16-bit connectors. Some systems had specialized connectors to speed up display and disk access. The Video Electronics Standards Association (VESA) bus and Extended Industry Standard Architecture (EISA) MLBs had connectors that supported higher speed transfers than the ISA bus connectors.

Now PCs incorporate both these evolutionary changes and revolutionary changes. Their MLB typically has Intel Pentium or AMD Athlon chips, RAM, ROM, built-in floppy disk, IDE fixed disk, USB, bus mouse, and keyboard controllers. PCs sometimes include a VGA controller and soundcard components as well. The chip sets and Basic Input/Output System (BIOS) support plug-and-play controller installation and sometimes a combination of ISA and Peripheral Component Interconnect (PCI) bus connectors. New MLBs are moving rapidly toward legacy-free configurations that support only plug-and-play PCI bus and USB components. This just means that it will not be your father's PC anymore. Also, maintenance and troubleshooting procedures change to accommodate new types of problems posed by these newer PC technologies.

System Board—MLB

The MLB, system board, or motherboard is the physical foundation of a computer. Baseboard, planar board, or main boards are other terms used to identify the MLB. It is the central PC building block because all other components must either plug into it or be physically mounted on it. Without a system board, no electrical interconnectivity is available to allow the PC's hardware components and subsystems to communicate.

System boards come in different configurations including:

• Extended Technology (XT) style

• AT style

• Baby AT style

• Advanced Technology Extensions (ATX) form factor and Mini ATX form factor

• Micro ATX form factor

• Flex ATX form factor

• NLX form factor

The early boards emulated an IBM PC XT configuration and then the IBM PC AT configuration. As chip sets incorporated greater functionality, MLBs shrank in size and, at the same time, incorporated more functions. The next generation of system boards had a standardized Baby AT form factor. This meant that they had one dimension that was from 8.6 to 8.8 inches and had specially placed mounting holes for plastic standoffs and bolts. Brand name PC manufacturers used proprietary system board configurations. Such proprietary configurations necessitated that replacement MLBs be provided from the PC manufacturer. These proprietary configurations limit the ability to upgrade PCs with faster CPU chips, RAM, and other capabilities. The ability to increase RAM, upgrade CPU chips, and swap adapter cards is designed into these proprietary MLBs, but such upgrade capabilities do not offer as many upgraded components as when an entire MLB is replaced. See Figure 1–2. For more detail on MLBs, see Chapter 5.

Figure 1-2 Baby AT Slot 1 and Socket 7 (with AMD CPU) MLB.

Today's PCs use MLBs that have ATX, Mini ATX, Micro ATX, Flex ATX, and NLX form factors. ATX form factor MLBs evolved from the Baby AT MLBs. Basically, the Baby AT MLB was rotated 90 degrees from its position facing the rear of a PC chassis, and a new power supply connection configuration was added. The longer ATX style boards permit relocation of the CPU and mounting of memory on the board. The longer ATX board also allows full-length expansion card slots and permits more I/O functions installed as components on the MLB.

ATX form factor MLBs have up to seven expansion slots and external connectors for the PS/2-style keyboard and mouse, as well as serial, parallel, and USB connections installed directly on the MLB. Some ATX form factor MLBs also include a sound card and added USB connections. Figure 1–3 shows a dual Slot 1 ATX MLB with the PS/2-style keyboard and mouse connectors on the lower-left bottom of the figure. USB connectors are next to the keyboard and mouse connectors. Communication (COM) port and parallel port connectors are near the middle of the ATX-style MLB. ATX MLBs are 12 inches by 9.6 inches with specially placed mounting holes for standoffs and bolts. Mini ATX MLBs were the first variation of the ATX MLB form factor. The Mini ATX MLB was 11.2 inches by 8.2 inches.

Figure 1-3 ATX Slot 1 MLB.

Micro ATX MLBs followed the Mini ATX MLB and are smaller still with a 9.6 inch by 9.6 inch maximum size. Similar to the ATX MLB, the micro ATX MLB has built-in connections for mouse, keyboard, USB, serial, and parallel connectors. It supports up to four expansion card slots that may be a combination of ISA, PCI, ISA/PCI, and Accelerated Graphics Port (AGP) bus slots. The MLB-installed components may include standard connections, as well as Musical Instrument Digital Interface (MIDI)/game and audio output connections.

The Flex ATX MLB is also a smaller board. Its dimensions are 9.0 inches by 7.5 inches. It has the same mounting as the Micro ATX MLB and the same standard ATX rear I/O panel. The smaller packaging of the Flex ATX reduces the overall system manufacturing costs, resulting in lower total system cost to the PC user.

NLX MLBs are designed for low-profile PC systems. They support current and future processor technologies, AGP, tall Dual Inline Memory Modules (DIMMs), and flexible installation without screws. An AGP bus connector may be mounted on the MLB, but ISA and PCI bus expansion slots cannot. Thus, a distinguishing NLX motherboard characteristic is that the PCI and ISA bus card slots are implemented in a riser card into which the MLB inserts. The NLX riser card can support up to five PCI bus slots and an unspecified (but low, like one or two) number of ISA bus slots. The expansion cards are inserted parallel to the MLB and not vertically into the MLB. The NLX motherboard may be 8.0 inches or 9.0 inches wide and 10 inches, 11.2 inches, or 13.6 inches long.

One key area of evolution for the MLBs is in the power supply interface. The older boards used a power supply with a built-in power switch. In this case, the high-voltage (120 or 220 Volts Alternating Current [VAC]) wires were only exposed if the power supply case was opened. Other AT-style power supplies had an external front panel switch. This meant that the high-voltage wires ran from the power supply to the front panel switch, exposing them whenever the PC case was open. The ATX power supplies terminate the high-voltage wires in the power supply and control the PC power on/off function through a low-voltage MLB control circuit and internal power relay. The front panel power switch plugs into the ATX MLB using a low-voltage connection. Viewing any of the main boards, you see sockets for the CPU chip (or the Intel Slot 1 and AMD Slot A carriers) and sockets for RAM, PCI, AGP, and sometimes ISA 16-bit bus connectors. Plugs for the power supply cables are also on the main board.

To examine a system board, a PC's cover must be removed. After you get inside, the system board typically is the largest sheet of green or brown fiberglass mounted directly to the metal frame or chassis. In an older desktop chassis, the system board was typically mounted on the bottom. With the newer tower configuration chassis, the system board is mounted vertically. System boards are multilayer boards with four to seven or more layers of connections sandwiched between the layers of fiberglass. All layouts have keyboard and mouse connectors in the right rear corner of the board. (If you were facing a desktop PC, the connections would be in the rear on the right.) See Figure 1–4.

Figure 1-4 Mini-tower chassis with control, Light-Emitting Diode (LED), and speaker connection detail.

Looking more closely, you will find a number of lines running across the system board in an organized pattern, connecting different areas of the system board together. Physically mounted on the system board should be a few different types of connectors and chips.

CPU

The CPU is a computer on a chip. The CPU chip acts as the hands or heart of the computer. There are no brains here because computers are dumb. They only do what they are told. They are the hands that perform the work as directed and the heart that pumps the data to all PC components.

Processors are classified by their interface to the MBL and by processing horsepower. MLB interfaces are a socket interface or a slot interface. The socket interfaces are Socket 7 (Intel Pentium CPUs) and Socket 8 (Intel PentiumPro CPUs). Intel introduced the Single Edge Contact (SEC) or slot interfaces in 1998. Most slot interfaces are Slot 1, but some Intel chips may use the Slot 2 interface, and AMD Athlon chips use a Slot A interface. Newer chips have returned to socket mounting with Intel's Socket 370, Socket 423, and Socket 478 and AMD's Socket A (Socket 462) mounting. See Figure 1–5. Processing horsepower is mostly defined by clock speed. CPU purists would argue that point vigorously. However, general users would only notice performance improvements when clock speeds increase by greater than 50 percent.

Figure 1-5 AMD Athlon Thunderbird CPU chip.

Other components in the CPU also determine its performance, including the amount of Level 1 (L1) and Level 2 (L2) CPU cache incorporated into the chip configuration.

Starting with the 486 chips, CPUs had internal Level 1 CPU cache memory to speed up processing performance. Both Level 1 and Level 2 cache are a storage area used by processors to increase performance. Level 1 is a small, high-speed cache right on the chip, which holds recently used data and instructions from memory. Level 2 is larger in size and, until recent years, has been located outside the chip on the motherboard. PentiumPro chips were among the first to include the Level 2 CPU cache in the chip package. The latest Intel and AMD chips have both Level 1 and Level 2 CPU cache memory inside the chip to maximize performance.

Cache memory is a means of speeding up computer processing. Cache works on the 80/20 rule of computers. This is similar to the 80/20 rule of the Internal Revenue Service (IRS). They keep 80 percent of what you earn, and you get 20 percent of what you earn. In computers, 80 percent of the time, the next piece of information that you need is right next to the last piece of information that you used. This means that, if information is contained on a device, like a disk drive, that is slower than the component where the information is going to be used next, like RAM, it makes sense to bring the information into a temporary holding area—the cache—that is faster than the disk drive. In this case, 80 percent of the time the data is retrieved from the cache, and 20 percent of the time the data is received directly from the slower disk drive. This is disk cache operation.

To really envision cache operation, think of baking cookies. You go to the cupboard and get flour, then go back to get sugar, and go again to get chocolate chips, and finally go to get spices. Next, it is on to the refrigerator to get milk, then butter, and, finally, eggs. How much would it speed up cookie baking if you went to the cupboard and got the flour, sugar, chocolate chips, and spices all at once and put them on the countertop, the cookie baking cache? You could then get the milk, butter, and eggs and also place them on the countertop as well.

CPU cache performs similar functions between the faster CPU and the slower RAM. Level 1 cache inside the CPU chip runs at the same speed as the CPU chip, but RAM is from three to 10 times slower than the CPU and the Level 1 cache. Even Level 2 CPU cache external to the CPU chip is half the speed of the CPU. Anything external to the CPU chip requires a relatively long time for the electrical signals to travel from it into the chip; that makes it much slower than anything inside the chip. It is similar to communication by satellite versus terrestrial links. Electrical signals must travel 44,000 miles across some satellite links versus 3,000 miles across a terrestrial link. It means that the signals require approximately 11 times longer completing the trip by satellite.

Most PC chips today are based upon the x86 instruction set developed by Intel. Manufacturers like AMD and VIA Technology's Cyrix produce chips that emulate the instruction set of the Intel chip. This is possible because of cross-licensing of technology and patents between manufacturers. All of these competing chips run PC software equally well. See Table 1–1.

Table 1–1 CPU Chip Summary

Chip	Multimedia Extensions(MMX)—Cache	Comment
Intel Pentium 4	Uses Intel Pentium III instructions with added multimedia instructions, has a special trace transfer cache, uses Rambus Dynamic RAM (DRAM), and is based upon copper technology	Intel's latest and greatest is no longer a Slot 1 cartridge. This chip is a Socket 423 or Socket 478 chip.
Intel Pentium III	MMX, Single Instruction-Stream, Multiple Data-Stream (SIMD) instructions, and internal Level 2 cache inside the cartridge	Best performance chip.
Intel Pentium II	MMX and external Level 2 cache inside the cartridge	Cheapest chip. This is a Socket 370 chip.
Intel Celeron 266/300	MMX, but no Level 2 cache	Cheap Intel. This is a slow performer.
Intel Celeron 300a/333/366/400/ 433/466/500/533/566/600/633/667/700/733/766/800	MMX and 128 kilobyte (KB) inside chip Level 2 cache	Cheap Intel. This is a competitive performer.
Pentium MMX	Initial MMX and external Level 2 cache	This is at the end of life.
Pentium Pro	No MMX and large internal Level 2 cache	This is a Windows NT server chip that is at the end of life.
Xeon Pentium III	MMX, SIMD instructions, and large internal Level 2 cache	New Windows NT/Windows 2000 server chip.
Itanium	Explicitly Parallel Instruction Computing (EPIC) architecture and 64-bit CPU. Has Level 1, Level 2, and Level 3 internal cache	Server chip for Windows NT/Windows 2000, Linux, and NetWare.
AMD-K6	Initial MMX and external Level 2 cache	Good Pentium MMX competitor.
AMD-K6-2	3D; improved MMX and external Level 2 cache	Good Pentium II competitor.
AMD-K6-3	3D; improved MMX and internal Level 2 cache	Best Pentium II competitor.
AMD-K7	3D; improved MMX and inside the cartridge Level 2 cache	Slot A design competitor to Slot 1
	Thunderbird chips have internal Level 2 cache	Newer Thunderbird chips return to socket technology and use Socket A or Socket 462.
Cyrix® M II	MMX and external Level 2 cache	Good for business applications, but poor for imaging and Computer-Aided Design (CAD). Less widely sold than AMD and Intel CPU chips.
Cyrix® III	3D; improved MMX and internal 128 KB Level 1 cache	The VIA Cyrix® III processor is designed for cheap PCs and notebooks, as well as the new generation of information appliances.

ROM

ROM contains the start-up code and the 16-bit BIOS programs for the PC. ROM is divided into system ROM installed on the MLB and adapter ROM installed on adapter cards. See Figure 1–6.

Figure 1-6 Keyboard and main BIOS ROM chips on MLB.

System ROM is first accessed during the boot process. It performs the initial PC setup, loads the PC's cold boot loader program from the fixed disk Master Boot Record (MBR), and handles the PC's I/O operations under the Disk Operating System (DOS). Most PCs have 64 KB of ROM. The addresses are mapped into the last 64 KB memory page below the memory boundary. Some PCs have more system ROM. The most notable was the Micro Channel Architecture (MCA) IBM PS/2. To operate the MCA bus and its jumperless hardware installation, 128 KB of ROM was used. The MCA bus PC was the predecessor to the PCI bus plug-and-play designs that we have today. Plug-and-play PCs use special ROM code to implement plug-and-play. This ROM code does not, however, increase the system ROM size beyond 64 KB. Other PC cards also contain ROM. Adapter ROMs perform special adapter card operations. They handle I/O operation, or, in the case of some Small Computer System Interface (SCSI) adapters, they perform setup and diagnostic operations. Adaptec has ROM on its SCSI adapters; SCSI Select software configures the adapter, functions as a diagnostic program, and formats the SCSI drives attached. Virtually all display adapters have some type of video ROM. This ROM is about 32 KB in size. It is placed in the PC address range 832 KB to 864 KB (C000-C7FF). More details on memory addressing and ROM locations are provided in Chapter 9.

RAM

RAM is the working area of the PC. All data must flow into and out of RAM. It holds both programs and data. When a program is running (executing) and working on data, the program and most often the data reside in RAM. In a Windows environment, RAM is virtualized. The operating system has 4 gigabytes (GB) of virtual memory where components and applications can reside. Windows translates the virtual address space into a combination of disk accesses and memory paging and allocation, translating the virtual address space into real physical PC RAM and disk addresses. When any PC is running, most of its electronic activity involves swapping data between RAM and the CPU. When the PC is powered down, the data in RAM is lost. The PC's maximum RAM capacity has moved from 1 megabyte (MB) to 16 MB and up to 4 GB or more today for many servers. Most PC RAM is comprised of DRAM chips that must be continually refreshed. Thousands of capacitors acting like leaky buckets comprise DRAM. Static RAM (SRAM) acts like small switches that, after they are set, do not need to be refreshed. SRAM is very fast and more expensive than DRAM. SRAM is used for external CPU cache.

Older forms of RAM employed a parity chip for error checking. The parity chip created an extra bit depending upon just how many ones are in the byte or character stored. When the character is read from memory, the parity is recomputed and compared to the originally stored value. If they matched, everything was OK. If they did not match, older PCs signaled "201" or "Parity Check 2."

Newer memory chips are placed on modules that are minicircuit boards called Single Inline Memory Modules (SIMMs), DIMMs, or Rambus Inline Memory Modules (RIMMs). SIMMs, DIMMs, and RIMMs provide an entire bank of memory on the minicircuit board. Replacement involves replacing the entire minicircuit board instead of a single bad chip.

RAM is rated and classified by access time. The slowest RAM chips were 250 nanoseconds (ns), and the fastest is around 10 ns. Typically RAM chip speeds are about 50 to 70 ns. For more details on RAM, see Chapter 5.

Other types of RAM are Synchronous DRAM (SDRAM) and Extended Data Output (EDO) RAM. These are both DRAM that needs refreshing. They are, however, more tuned to the CPU chip's clocking and memory refresh operations and therefore speed up the PC by reducing CPU to memory transfer times.

Newer RAM types are Double Data Rate RAM (DDR RAM) and Rambus DRAM. DDR RAM moves data on every bus clock signal change, not just on leading edge changes. SDRAM operates at 100 megahertz (MHz), and the equivalent DDR RAM would then operate at 200 MHz. Rambus DRAM is a new RAM technology that increases RAM speed to 400 MHz or higher. The higher RAM operating speed does not necessarily mean that Rambus DRAM PCs are faster than DDR RAM PCs because the delay increases when accessing different parts of Rambus DRAM.

Nonvolatile RAM (NVRAM)

There is also NVRAM. This is similar to ROM in that it does not lose its contents when the PC is powered off. NVRAM is SRAM that retains its databits as long as power is supplied to the memory. NVRAM contents are saved when a computer is powered off or its external power is lost, and it is implemented using SRAM with battery power or by using an electrically Erasable Programmable ROM (EPROM).

Like RAM, NVRAM can also be written into. However, writing into NVRAM requires special software. Hence, NVRAM is used to hold ROM BIOS code that may need to be updated or changed. Flashing programs with names such as PHLASH and AWDFLASH update this information. Some modems store preset or user-specified phone numbers and modem profiles using NVRAM. They are specially designed to write the information into NVRAM without using a separate flashing program.

The BIOS is implemented in ROM or NVRAM. It is the code in the PC that boots the PC and controls I/O operations under DOS. Windows uses 32-bit driver software to perform the functions of ROM BIOS routines. The original PC BIOS had a built-in Basic interpreter program for the Basic programming language. Around 1990, that Basic interpreter code disappeared from even the IBM PC's BIOS. BIOS could be considered as only that part of ROM controlling I/O functions in the PC. However, a broader view would define BIOS functions as:

• Hardware setup—During boot, the PC allows you to enter hardware setup options and configure the PC's standard and advanced hardware options.

• Power-On Self-Test (POST) diagnostics—Performs cursory hardware testing to ensure that the PC hardware matches the setup parameters. These diagnostics are only effective in detecting major PC component malfunctions.

• Cold boot loading functions—Loads DOS from a diskette or loads the cold boot loader program from the fixed disk's MBR. It also loads the initial disk drive parameters from the fixed disk partition table.

• DOS I/O operations—Provides basic floppy disk, keyboard, display, and fixed disk I/O control operations.

With Windows, these BIOS functions are used during the initial system startup and then replaced by Windows 32-bit driver software.

Firmware

Firmware is PC component driver programs installed in ROM or NVRAM. Firmware was initially used to store hardware setup and BIOS routines because it was easier to update than hardware. In contrast, software stored on disk is the most flexible and easy to change. Firmware typically controls a PC when it is first switched on. Typical firmware would perform cold boot loading of the operating system from a fixed disk or from a network and then pass control to the operating system.

Complementary Metal Oxide Semiconductors (CMOS)

CMOS really describes a chip technology that uses low power. This technology was originally employed in the PC AT to store hardware configuration information in a nonvolatile battery-powered memory chip. A three- or six-volt lithium battery powered the CMOS memory chip. Today, CMOS technology is used in chips in almost all PCs to reduce power consumption. "CMOS" as a term is used to identify the PC's nonvolatile parameter storage memory, initially implemented with CMOS technology. See Figure 1–7.

Figure 1-7 CMOS batteries.

When the PC is booted, the setup software implemented in ROM changes the PC operating parameters in CMOS memory. These parameters and the CMOS memory addresses are mapped into the first 64 KB memory bank. CMOS is much smaller than 64 KB. Most ROM BIOS setup programs automatically detect disk drive types and CPU speeds and set the PC up to run. CMOS setup parameters are not required for basic PC operation, but rather to tweak the PC for optimal performance. Be careful when changing any CMOS settings because, most often, what seems to be the best or fastest setting can cause the PC to go slower or to malfunction. Default CMOS operating parameters and automatically detected parameters are always the best bet when setting up a PC.

Onboard Controllers

MLBs have built-in controllers for the keyboard, a bus mouse, serial ports, parallel ports, floppy disk drives, IDE fixed disk drives, CD-ROMs, and USB ports. Some servers have onboard SCSI controllers as well.

The first onboard controllers were for the keyboard and the serial and parallel ports. Next, systems incorporated bus mouse ports and floppy and fixed disk drive controllers. These ports were initially routed to outside the PC chassis by pigtail connectors that fit into the expansion slot card covers at the rear of the PC. Such pigtail connections were used on Baby AT system boards. Disk drive controllers had parallel cables attached directly to the stake pin connectors on the MLB. Today, these onboard controllers have their ports directly routed to a special connector area at the right rear of the MLB. This is an ATX MLB configuration.

MLBs typically had two Enhanced Integrated Drive Electronics (EIDE) controllers as shown in Figure 1–8. EIDE onboard controllers have increased transfer speed from 33 MHz Direct Memory Access (DMA) clock speed to 66 MHz DMA and 100 MHz DMA speeds. The number of MLB integral EIDE controllers has also doubled from two to four controllers on some MLBs. This permits those MLBs to support up to eight EIDE devices. The best performance is realized by assigning a single EIDE device to each controller. For example, two fixed disk drives, a DVD drive, and a CD-RW drive could be each connected to a separate EIDE controller to maximize performance because EIDE commands could be executed concurrently, which speeds up copying data from drive to drive.

Figure 1-8 MLB primary and secondary IDE bus connectors.

Expansion Slots

Expansion slots implement the PC's system bus. The system bus connectors allow other circuit cards to be plugged into them. Because they are card edge connectors, they are called expansion slots. The cards inserted in the edge-style bus connectors are referred to as daughter cards or expansion cards. The daughter card label was used because the cards were inserted into the motherboard.

The expansion slots had different configurations depending upon the bus supported by the system board. The simplest configuration was the 8-bit ISA bus used in the original PC. These bus expansion slots evolved to a 16-bit ISA bus and then on to a 32-bit EISA configuration. The physical size of the EISA slots was the same as the 16-bit ISA slots except the EISA slots permitted the expansion cards to plug deeper into the connector. Thus, EISA slots could support 8-bit, 16-bit, and 32-bit I/O transfers. Table 1–2 identifies expansion slots found in different PC systems.

Table 1–2 Expansion Slot versus PC System

Expansion Slot or Bus	PC System
ISA 8 bit	PCs and XTs
ISA 16 bit	ATs
EISA	386 and 486
ISA 16 bit + VESA Local (VL)-Bus	386, 486, and Pentium
EISA + VL-Bus	386, 486, and Pentium
ISA 16 bit + PCI	Pentium Class PCs built in 2000 and before 2000
PCI	Pentium Class PCs built after 2000
EISA + PCI	Pentium—Servers
Personal Computer Memory Card Industry Association (PCMCIA) or Card Bus	Laptops
MCA 16 bit	PS/2—old
MCA 32 bit	PS/2—new
AGP	Pentium class PCs built after the late 1990s

In early PCs, expansion slots were used for virtually all upgrades to the PC's basic capabilities, including RAM expansion. I had a PC AT that had 12 MB of RAM installed on several RAM expansion cards. The maximum RAM supported by the PC AT 80286 chip was 16 MB. This is not possible with today's PCs because RAM transfer to the CPU chip is at much higher speeds than the expansion slots and their buses can run. The top bus clock speed has increased from 8 MHz, to 33 MHz, to 66 MHz, and to 100 MHz. Front side bus (the CPU to RAM bus) speeds have increased from 66 MHz, to 100 MHz, to 133 MHz, to 200MHz, to 266 MHz, and to 400 MHz. This is slow when compared to the 1.5 gigahertz (GHz) and higher clock speeds of CPU chips.

Expansion slots are used to install disk controllers, display controllers, modems, video capture, and LAN adapter cards in the PC. Each type of adapter card enhances the functionality of the basic PC system. These adapters typically run at speeds that match the bus clock speed.

Typical PC expansion slots include ISA 16-bit, PCI, and AGP slots. See Figure 1–9.

Figure 1-9 PC MLB ISA 16-bit, PCI, and AGP expansion slots.

Power Supply

The PC power supply converts 120/240 volt Alternating Current (AC) into the 5- and 12-volt Direct Current (DC) used by the PC. Power supplies are rated by wattage. They range from 85 watts for the original PC to 300 watts for high-end PC power supplies. A watt is a power measurement that is voltage times the amperage delivered by the supply. Because voltage is the same for all supplies, a higher wattage translates into more current being delivered by the supply.

The original PC chips operated using Transistor-to-Transistor Logic (TTL) re-quiring 5-volt DC. The CPU chips of today's PCs can use lower voltage levels. Typically, these chips employ special voltage regulation incorporated into the MLB.

The original PC power supplies had built-in power on/off switches and power connectors for the MLB and the disk drives. As the PC changed, the power supplies did, too. Current power supplies are typically 230 to 250 watts. They have power connectors for either an AT-style or an ATX-style MLB. Additional power connectors support fixed disk drives, 3.5-inch floppy drives, and front panel lights. Each such connector has a different physical configuration. Furthermore, the power on/off switch is no longer on the side of the supply, but rather mounted on the front of the PC. See Figure 1–10. This necessitates an insulated power connection to a front panel PC power switch. As discussed earlier in the System Board—MLB section of this chapter, newer ATX-style MLBs control the power on/off function by a low-power connection to the MLB. For further discussion on the types of connectors, see Chapter 5.

Figure 1-10 AT-style power supply with front panel switch.

Fixed Disk Drives and Controllers

The fixed disk drive is the file cabinet of the PC. It is the device that holds all software and data while the PC is running and after the PC is powered down.

Fixed disks are described by their capacity, speed, physical size (form factor), and controller interface. Fixed disk capacities range from 8 GB to more than 80 GB. The largest IDE drives are over 80 GB in capacity. Fixed disk drives have Power-On Hour (POH) Mean Time Between Failure (MTBF) rates ranging from 150,000 POH to 1,000,000 POH.

Fixed disk speed is measured by the time it takes for the disk drive read-write heads to seek the data on the disk and the time it takes to transfer data from the disk to the PC's disk controller. Head seek times are influenced by the physical size of the drive, with smaller drives having better seek times because the read-write heads have shorter distances to travel. Typical seek times range from 8 milliseconds to just over 10 milliseconds. Fixed disk transfer rate is largely determined by the rotational speed of the disk. Disk drives originally rotated at 3,600 Revolutions Per Minute (RPM).

Today's disk drives range in rotational speed from 4,500 RPM to 15,000 RPM. The higher the rotational speed means the higher the disk drive transfer rate.

The physical size of the disk drives ranges from 1 to 2.5-inch quarter-height drives, to 3.5-inch third or half-height drives, and on to 5.25-inch full-height drives. Other form factor combinations exist as well. The form factor describes the size of the disk—1 inch, 2.5 inches, 3.5 inches, and 5.25 inches—and the height of the drive, with a full-height drive being 3.25 inches high.

Fixed disk drive interfaces are most often IDE, EIDE, or SCSI.

IDE and EIDE

Disk drive interfaces started with the Modified Frequency Modulation (MFM) interfaces that were standardized by the Seagate ST-402 and ST-512 specifications. These interfaces required two cables to the disk drive from the disk controller card. One cable (the wide one) handled 8 bits of data and the drive control signals, and the other (the narrow one) handled the second 8 bits of data. The data and control cable were an extension of the floppy disk interface. It was a 34-conductor cable. The second data-only cable was a 16-conductor cable.

IDE interface disk drives having the drive controller built on the drive displaced MFM drives within a few years. This integration of controller and drive greatly simplified the control interface in the PC. The IDE interface is used today for both fixed disks and CD-ROM drives. It employs a single 40-conductor cable. See Figure 1–11. EIDE controllers provide improved transfer speeds and the ability to interface to four drives.

Figure 1-11 IDE drive cable connection.

Today, IDE and EIDE interfaces can burst transfer data at 33, 66, or 100 MB per second. The largest IDE drives are around 80 GB, with their size expected to increase in the next few years. IDE and EIDE drives are the most commonly installed drives in PCs.

SCSI

Apple pioneered the SCSI. It was used to connect peripherals to Apple computers. This was the SCSI-I interface that transferred data at 5 MB per second. SCSI became the interface of preference for large-capacity drives. SCSI was relatively expensive because not only were the drives expensive, but they required the addition of a SCSI interface card.

The great advantage of the SCSI besides the increased drive capacity was the ability to connect up to seven drives on the same SCSI interface. This made it possible to build much larger disk volumes and to implement Redundant Array of Independent Disk (RAID) drives. The first CD-ROMs employed SCSI interfaces, but they have since migrated to the EIDE interface.

Many SCSI drives use a single 50-conductor parallel cable with terminating resistors at each end of the bus, which is often the end of the cable. This cable has changed as the SCSI interface speed increased. SCSI started with the Apple SCSI-I speed of 5 MB per second. Early PC SCSI drives operated at this speed. Because the SCSI bus was shared, the transfer speed increased rapidly to provide adequate PC performance. The SCSI bus was changed to fast operation, increasing the transfer speed to 10 MB per second. The fast SCSI set the basic clock rate for the SCSI interface at 10 MHz. The SCSI-II PC controllers operated at this speed. They transferred one byte at a time at 10 MHz, thus producing the 10 MB per second transfer rate.

The SCSI interface was upgraded to the fast wide SCSI that transferred 16 bits, increasing SCSI bus speed to 20 MB per second. The next enhancement was to improve the fast operating speed to 20 MHz with the 16-bit ultrawide SCSI bus, thus providing 40 MB per second transfers. Finally, we have Ultra-2 SCSI capable of 80 MB per second transfers, accomplished using a 40 MHz bus or a 32-bit bus operating at 20 MHz. The SCSI cables changed from the original 50-conductor cable to a 68-conductor cable and finally to fiber optic SCSI channels.

SCSI drives and interfaces are prevalent and preferred in high-end PC and network servers requiring RAID and high-capacity drives. Because the SCSI bus is shared, the transfer speeds of the fastest SCSI buses are divided among the drives attached to the controller. Depending upon the PC use, such a division might enhance overall PC performance. Such enhanced performance, while measurable, is not likely noticeable by most users.

Table 1–3 provides a summary of these interfaces, their characteristics, and their differences.

Table 1–3 Interface Types and Characteristics

SCSI Type	Bus Speed	Bus Width	Connector	Throughput	Distance of Cable Single Ended	Number of devices
Regular SCSI	5 MHz	8 bit	50 pin	5 MB/sec	6 meters	8
Wide SCSI	5 MHz	16 bit	68 pin	10 MB/sec	6 meters	16
Fast SCSI	10 MHz	8 bit	50 pin	10 MB/sec	3 meters	8
Fast wide SCSI	10 MHz	16 bit	68 pin	20 MB/sec	3 meters	16
Ultrawide SCSI	20 MHz	16 bit	68 pin	40 MB/sec	1.5 meters	16
Ultra-2 Wide SCSI	40 MHz	16 bit	68 pin	80 MB/sec	12 meters, but must be LVD cabling	16

Three types of cabling are most used with SCSI: single ended, differential, or Low Voltage Differential (LVD). Single ended has been the most commonly used through the years because of its low cost in comparison to differential. Now, with the higher speeds, single ended is very limited in the distance of cabling. Differential cabling is more expensive then single ended, but can do all speeds up to 25 meters, so it is used in long runs of external cabling. LVD is relatively new on the market and is supposed to have the best of both worlds because it can run all speeds of SCSI up to 12.5 meters at a much lower cost than differential. Remember, do not mix your SCSI cabling types; they are electrically incompatible.

Microdrives

New, very small fixed disk drives are being used in a variety of electronic equipment. Pioneered by IBM, microdrives provide 340 MB to 1 GB storage capacity for portable electronic devices in an industry-standard Compact Flash + (CF+) Type II form factor and an AT Attachment (ATA)/PCMCIA Type II interface support with appropriate adapter. The high-capacity microdrives enable digital cameras to capture more high-resolution photos, enable handheld PCs to access more applications and to maintain large databases, and permit notebook users to back up and to transport their data more quickly and conveniently. A single hard disk microdrive can provide 340 MB, 512 MB, or 1 GB storage capacity in about a 1.5-inch square 16-gram package. Microdrives support a maximum sustained data rate exceeding 4 MB per second.

JAZ and ORB

Iomega developed JAZ drive technology. JAZ drives are floppy disks that rotate at high speeds (5,394 RPM vs. 300 RPM for floppy disk drives). They employ the Bernoulli principle (fast moving air has less pressure than static air, which is what causes planes to fly) to permit the read-write heads to get very close to the floppy disk medium. As a result, they can store substantial amounts of data on 3.5-inch floppy disk cartridges. Because their rotational speed is high compared to floppy drives, they have performance that resembles fixed disks. The newer JAZ drives are capable of storing 2 GB of data on a single removable floppy disk cartridge. JAZ drives interface to the PC using SCSI. See Figure 1–12. JAZ drives can be installed internally or attached externally to the PC. External drives can be moved from PC to PC, using a USB or a FireWire (Institute of Electrical and Electronic Engineers [IEEE] 1394) interface to connect to the PCs. The older JAZ drives interfaced to the PC using the PC's parallel port, and the PC's parallel interface was transformed into a SCSI interface using a special Trantor interface cable. JAZ drives have a MTBF of 250,000 POH.

Figure 1–12 JAZ® drive, cartridge, and SCSI interface connectors.

JAZ drives provide removable media storage for PC backups. The benefit of such backup is that the JAZ drive's operation is similar to random access disks and not like linear access tape backups. Random access can make data accessibility faster than with tape. The limitation here is that each cartridge stores only a maximum of 2 GB of data. JAZ cartridges can be compressed, but this presents problems for the 2-GB capacity cartridges. Because JAZ drives look like older DOS fixed disks to the PC, they are limited to storing only a maximum of 2 GB of data effectively. Thus, when a 2-GB cartridge is compressed, it produces a 2-GB drive and 1-GB hidden drive. The 1-GB drive is usable, but not conveniently so. It is much more effective to compress a 1-GB JAZ cartridge to provide about 2 GB of storage. The 2-GB JAZ drive works with the 1-GB JAZ cartridges.

The ORB drives from Castlewood also store 2.2 GB of data. They perform similarly to the JAZ drives. ORB drives connect to PCs using EIDE and SCSI interfaces for internal drives and SCSI, USB, and FireWire for external drives.

Optical Rewriteable Drives and DVD-RAM Drives

Optical storage drives are similar to JAZ drives. They have an equivalent 2-GB capacity or greater, and they rotate at higher speeds than floppy drives, from 2,400 RPM to 3,755 RPM. (Sony's external optical drive runs at 3,600 RPM.) Rewriteable optical drives use a SCSI interface like the JAZ drives.

Optical rewriteable drives store data using a magneto-optical storage process. Magnetism is used to permit laser recording of data on the disk media. After it is recorded, the data is read using a laser. The main benefit here is that the recording medium is durable and lasts a long time. Where data in time can be corrupted on JAZ floppy media, it is good for 30 years on rewriteable optical media. The rewriteable optical cartridges use 5.25-inch media that may hold 650 MB, 1 GB, 1.3 GB, 2.6 GB, or 5.2 GB. This is physically larger than the JAZ 3.5-inch media.

The rewriteable optical technology has migrated from the original rewriteable optical drives to rewriteable CD drives (compact disc-erasable [CD-E]) and rewriteable DVD drives. The rewriteable CD drive provides more flexibility and storage capacity at a reduced cost than the original rewriteable optical drives, using a 5.25-inch media similar to a CD. It has the CD recording capacity of 600 to 700 MB. The media does not require a special carrier (container for the media), which the optical rewriteable drive does. Performance is similar to a slower CD-ROM.

Rewriteable DVD drives (also called DVD RAM drives) provide greater storage capacity than other rewriteable drives. Similar to a normal DVD drive, they use a blue laser to enhance storage capacity of the 5.25-inch media. The discs can store 2.6 GB on single-sided discs and 5.2 GB on double-sided discs. They can read and write DVD media and read CD-ROM media. Disc formats supported are DVD-RAM, DVD-R, DVD-ROM, CD-ROM, CD-RW, CD-Extra, and CD-Audio (CD-A). The interface to the PC is typically SCSI for these devices. DVD-RAM drives use rewriteable cartridges that are most commonly sold in a 5.2 GB, double-sided capacity. Some DVD RAM drives have a MTBF of 100,000 POH.

Floppy Disk Drives

Floppy disk drives were the original PC storage media. From 1981 through 1983, there were no PC fixed disk drives. The first fixed disk drive that we saw for a PC was a 5-MB drive that cost $5,000. Months later, IBM marketed the PC XT with its 10-MB fixed disk for $1,000. In the 1981 to 1983 timeframe, we first used single-sided and then double-sided floppy drives as the only permanent data storage for the PC. Of course, everything was smaller then. A large file was 30 KB because it contained ASCII text-only information.

5.25-Inch Floppy Drives

The original PC disk drives stored 160 KB of data on a single-sided 5.25-inch disk. They used 40 tracks with eight sectors per track with each sector storing 512 characters (bytes) of data. The total capacity then was (40 tracks) x (8 sectors) x (.5 KB), equaling 160 KB total capacity. At one time, we were so desperate for storage space that we attached four double-sided floppy disks to a PC. It was the ultimate machine at the time because of its active 1.44-MB storage capacity. See Figure 1–13.

Figure 1–13 5.25-inch floppy disk drive.

These disks were soon replaced by double-sided drives, then nine sector-per-track drives, and, finally, by high-density 5.25-inch drives. Each disk drive enhancement increased the storage capacity. The high-density drives appeared with the PC AT. They stored data on 80 tracks with 15 sectors per track on two sides of the floppy. As always, the sectors contained 512 characters of data. Their capacity was (80 tracks) x (15 sectors per track) x (two sides) x (.5 KB), equaling 1.2 MB per disk.

The disks came in a plastic holder that provided the necessary mechanical support for inserting them into and removing them from the floppy disk drive. A paper sleeve protected the floppy media by covering the read-write window of the diskette.

3.5-Inch Floppy Drives

The 3.5-inch floppy drives came out with the first IBM PS/2 PCs in 1987. They were about two-thirds the width and one-half the height of a 5.25-inch drive. They had new power connections requiring special power supply pigtail adapters to provide power to the drives. Today, all power supplies provide specific 3.5-inch disk drive power connections. The 5.25-inch drives used both 5-volt and 12-volt DC power, while the 3.5-inch drives used 5-volt DC power alone. See Figure 1–14. Some 3.5-inch drives were even smaller in height, and combination 3.5-inch and 5.25-inch drives were developed that fit into a single 5.25-inch half-height drive bay.

Figure 1–14 3.5-inch floppy drive.

The 3.5-inch disk media is mounted in a permanent plastic sleeve with a special sliding door protecting the disk drive media. The sliding door is one of the greater hazards for 3.5-inch drives. The doors are typically made out of aluminum or plastic that is easily bent or broken. Any bending makes the aluminum door catch on the inside of the 3.5-inch drive, causing destruction of the disk and sometimes damage to the drive itself.

The 3.5-inch disk stores data on 80 tracks with 18 sectors per track. This gives a total capacity calculated by multiplying (80 tracks) x (18 sectors per track) x (two sides) x (.5 KB), equaling 1.44 MB per disk. These disks have become, in the late 1990s, the basic DOS boot and initial software installation mechanism for PCs. Their capacity today remains adequate for hardware diagnostics, but it has become insufficient for installing any software. Software installation is largely from CD-ROMs. Newer PCs can boot directly from the CD-ROM to facilitate direct software installation. Some of the latest floppy disk drives rotate at about twice the speed of older floppy drives. This significantly enhances their performance. Their capacity has not been increased, only their data transfer and seek time performance. Newer super disk drives, resembling floppy drives, do enhance both disk capacity and performance.

The typical mean time between failures for a floppy disk drive is 30,000 POH.

Super Disk or Laser Servo (LS) 120 Drives and High Floppy Disk (HiFD) Drives

The Imation, Inc. Super Disk or LS-120 drives stored 120 MB of data on special floppy disks, and Sony's HiFD can store 200 MB on its special floppy disk. These drives accomplish this by increasing the track density and the sectors-per-track storage density on the floppy media. A more precise LS head positioning mechanism makes this possible. The Super Disk 3.5-inch disks store data on 1,736 tracks with 69 sectors per track. This gives a total capacity calculated by multiplying (1,736 tracks) x (69 sectors per track) x (two sides) x (.5 KB), equaling 119.784 MB per disk.

Super disk drives interface to the PC using either the IDE/ATA Packet Interface (ATAPI), similar to CD-ROMs, or the parallel port, similar to Zip drives. Their performance is similar to parallel interface Zip drives. Super disk drives rotate at 720 RPM, about twice the speed of the older floppy disk drives. The higher rotational speed improves disk drive performance, making super disk drives faster than floppy drives, but somewhat slower than Zip or JAZ drives. Sony's HiFD drives connect to the PC using a parallel or USB interface.

In spite of their increased capacity, super drives still lack the storage space to act as an effective installation medium for most Windows application programs. Newer applications occupy several hundred MB of disk storage space, thus requiring the storage space on CD-ROMs or on DVD-ROMs to contain the software and supporting data being installed.

Because of the increasing need for storage capacity, Imation stopped selling super disk drives in 2000. Our guess is that these high-capacity, fast floppy disk drives that are backward compatible with 3.5-inch floppies are most likely to be relegated to a niche market in the long run.

Zip Drives

Zip drives, similar to super disk drives, originally stored 100 MB of data. Newer Zip drives store 250 MB in a 3.5-inch disk cartridge. There are Zip 250 drives that store either 100 MB or 250 MB of data. Zip drives interface to the PC using either a parallel port or SCSI connection. A new USB 100 MB Zip drive is also offered. The Zip 250 drive operates using the original Zip SCSI or parallel port connection. The Zip drives, just like JAZ drives, work based upon the Bernoulli principle, permitting the read-write heads to move close to the floppy recording media and thus providing the ability to store more information and to provide high performance without damage to the media. Zip drives rotate at 2,945 RPM. Their performance is better than the super disk drives due largely to their rotational speed.

The PocketZip™ drives use smaller 2-inch by 2-inch disk cartridges that store 40 MB of data. Similar to microdrives, the PocketZip drives connect to PCs using USB interface.

CD-ROM

CD-ROMs have become a standard part of every PC. They are about to be displaced by the newer higher capacity DVD drives because of the growing need for more information storage capacity on PCs. Such increased information storage capacity will be used to store video (movies) and large databases. For example, the American Automobile Association (AAA) Map 'n Go software that stores road maps of the United States and Canada on a single CD-ROM is limited by the CD-ROM's capacity. Therefore, detailed street maps are only provided for specific areas surrounding major cities. The DVD version can have detailed street maps for virtually the entire United States.

Typical CD-ROMs store about 650 MB of data (or 74 minutes of audio recording in CD-A format) on a read-only 5.25-inch plastic media. CD-ROM drives read discs with CD-ROM, CD-RW, CD-Extra (a format supporting a mix of CD-A and CD-ROM information), Motion Picture Experts Group (MPEG) Audio Layer 3 (MP3), and CD-A.

CD-ROMs have become the primary distribution mechanism for virtually all PC software. With the advent of high-speed Internet connectivity, the software distribution and update methodology will change to an Internet focus because of the convenience. This will extend NVRAM upgrading for different hardware devices. For example, we recently upgraded a 3Com-USRobotics modem to the current firmware release by connecting to the 3Com site through the Internet and then dialup communications.

The 1X speed, 2X speed, and higher speed CD-ROM drives are measured relative to the original rotational speed of audio CDs. The 1X CD drives rotated from 210 RPM to 539 RPM, providing Constant Linear Velocity (CLV) as the CD was read from the outside to the inside tracks on the CD. Audio CD specifications are the basis for all CD standards. Higher X speeds mean faster writing speeds. When reading, access and seek times are often better for higher X speeds. Fixed disk drives behave differently. They rotate at one constant speed, producing variable data rates (Constant Angular Velocity [CAV]) as the data is read from the outside to the inside tracks on the disk.

CD-ROMs interface to the PC using the IDE/ATAPI interface. They occupy a single 5.25-inch half-height drive bay. CD-ROMs perform at different speeds and with different data-buffering capabilities. The top speed CD-ROM drives are 72X drives as compared to the original 1X and 2X speed drives. Some drives advertise higher speeds. They accomplish the higher speeds through buffering of data read from the CD-ROM drives. CD-ROMs rotate at variable speeds depending upon the track being read. The rotational speed varies from about 539 RPM to 210 RPM for a 1X drive, with the inside tracks being read at the higher rotational speed. This technique maintains a CLV of the data as it travels under the CD-ROM read heads because inside tracks have less data than outside tracks.

Different types of CD-ROMs have different CD storage formats. CD-ROM formats differ for CDs storing audio only, data, CD-R (Compact Disc-Recorders) data, and CD-RW data. There are also variations for storing photos (Kodak Photo CDs) and video.

CD-R (CD-RW/CD-R) Drives

CD-R drives write and read CD-ROMs. The original CD-R drives have been replaced by the CD-RW drives that can function as a CD-R drive, writing once on CD-R media, and, with the proper CD-RW media, they can write and rewrite recordable CDs. CD-RW drives read prerecorded CD-ROMs, both audio and data, and write and then read recordable CDs. The reading process is at a higher speed than the writing process. CD-RW drives operate at different speeds for reading CDs (up to 40X), writing CD-ROMs (up to 16X), and writing CD-RW media (up to 10X). The first CD-R drives interfaced to the PC using a SCSI bus connection. Most CD-RW drives use the IDE/ATAPI interface standard used by CD-ROM drives. Special software is required to perform the CD writing operation. This software writes data and audio CDs. CD-RW drives require a single half-height 5.25-inch drive bay for mounting in a PC. See Figure 1–15.

Figure 1–15 CD-R drive.

The major benefit of having CD-RW drives is that they can act as a backup for valuable data. In spite of their storage capacity being somewhat limited (650 MB), they are cheap (about $1 per disc) and very transportable. If properly cared for, the life expectancy can be as long as rewriteable optical drives.

There are different types of CD-R discs. Not every type of disc works with every CD-RW drive at the highest recording speed. To ensure that a disc works with a specific drive, you should perform a test of that manufacturer's media. Often, reducing the recording speed helps in recording the data. CD-RW drives have a MTBF of 30,000 to 60,000 POH.

DVD

DVD discs are similar in capabilities to CD-ROMs, but they are capable of storing significantly larger amounts of data. This is possible because they use a different color laser and because they can store data on both sides of the disc. This makes it possible to store 5.2 GB, 8.5 GB, 9.4 GB, or 17 GB of data on a single DVD disc. The single-sided DVD discs store 4.7 GB or 9.4 GB. When reading DVD discs, the drives run at slower speeds than when reading normal CD-ROMs. The DVD reading speeds are up to 16X, while CD-ROM speeds are as high as 72X.

DVD drives support a full variety of DVD and CD formats, including DVD-ROM (DVD-4.7, 8.5, 9.4, and 18), DVD-ROM book, DVD-Video book, CD-Digital Audio (CD-DA), CD-Graphics (CD-G), CD Text, CD-ROM, CD-ROM-Extended Architecture (CD-ROM-XA), CD-Interactive (CD-I), Photo CD, Video CD, CD-R, and CD-RW. This provides backward compatibility with older CD-ROMs and forward compatibility with the enhanced storage capabilities of the newer DVD CDs. Combination DVD and floppy drives are used in laptops. This dual DVD/floppy drive occupies a single laptop PC drive bay. Similar to CD-ROM drives, DVD drives have a MTBF of 100,000 POH.

Disk Drive Summary

Disk drive capabilities are summarized in Table 1–4.

Table 1–4 PC Disk Drives

Type of Drive	Media Size	Approximate Rotational Speed	Interfaces	Capacity	Physical Drive Size
5.25-inch floppy	5.25-inch disk	300 RPM	Floppy disk	160 KB to 1.2 MB	5.25-inch half-height drive; 5.25-inch quarter-height drive (combination units)
3.5-inch floppy	3.5-inch disk	300 RPM	Floppy disk	720 KB to 1.44 MB	3.5-inch half-height drive; 3.5-inch third-height drive; 3.5-inch quarter-height drive (combination units)
LS-120 Super Disk	3.5-inch disk; 3.5-inch Super Disk	300 RPM and 720 RPM	Parallel IDE	1.44 MB and 120 MB	3.5-inch half-height drive
Microdrives	CF+ Type II that fits a PCMCIA Type II slot with an adapter	3,600 RPM	PCMCIA Type II	340 MB to 1 GB	5 mm 43 mm 37 mm
Fixed disks	1-inch to 5.25-inch	3,600 RPM to 15,000 RPM	IDE EIDE SCSI	10 MB to 80 GB	5.25-inch full-height to 1-inch quarter-height
CD-ROM	5.25-inch disk	210 to 539 RPM for 1X and 3,360 to 8,624 RPM for 16X	IDE SCSI	650 MB	5.25-inch half-height drive
CD-RW CD-R	5.25-inch disk	210 to 539 RPM for 1X and 3,360 to 8,624 RPM for 16X	IDE SCSI	650 MB	5.25-inch half-height drive
Optical CD-E	5.25-inch disk	2,400 to 3,755 RPM	IDE SCSI	2.3 GB per side or 4.6 GB total	5.25-inch half-height drive
DVD-RAM	5.25-inch disk	210 to 539 RPM for 1X and 1,100 to 9,200 RPM for 16X	IDE SCSI	2.6 GB one side 5.2 GB two sides or 4.7 GB one side 9.4 GB two sides	5.25-inch half-height drive
DVD-R	5.25-inch disk	210 to 539 RPM for 1X write and 420 to 1,078 RPM for 2X read	SCSI	3.95 GB and 4.7 GB	5.25-inch half-height drive
JAZ	3.5-inch cartridge	5,394 RPM	IDE SCSI	1 GB to 2 GB	5.25-inch half-height drive
Zip Zip 250	3.5-inch cartridge	2,945 RPM	IDE SCSI USB	100 MB to 250 MB	3.5-inch half-height drive
DVD	5.25-inch disk	1,200 to 9,200 RPM as a DVD 9,500 RPM CD-ROM	IDE	4.7 GB (single layer, single side), 8.5 GB (dual layer, single side), 9.4 GB (single layer, double side) and 17 GB (double layer, double side)	5.25-inch half-height drive

Tape Drives

PCs sometimes come with tape drives for making backups of data on the fixed disk drives. Tape drives store data sequentially on Digital Audio Tape (DAT) tape cartridges. The DAT standard, created in 1987, is a digital recording format providing three hours of digital sound on a tape half the size of an analog cassette tape. The recording format uses a 44.1 kilohertz (KHz) sampling frequency; 16 bits is the same format used to record CD-ROMs.

Tape drives can store from 4 GB to 40 GB of data per cartridge. They use 4 mm DAT or 8 mm DAT tape cartridges, both of which can store up to 40 GB. Tape drives interface to the PC using SCSI interfaces or IDE interfaces.

Sound Cards

All PCs today have the capability to create and record sound. Sound cards installed in the PC provide this capability. Early sound cards were mainly used to produce sounds for Windows activities and to play CDs. Today's sound cards turn a PC into a programmable stereo system when it is connected to powered speakers. With the software and music data storage formats available, the PC becomes a programmable stereo system capable of producing three-dimensional sound. Sound stored in an MP3 format is greatly compressed. CD stereo music can be compressed by a factor of 12 compared to the files produced when sounds are directly recorded.

The original sound file format was a Windows Audio Volume (WAV) format used by the Creative Labs SoundBlaster sound cards. A more compressed format was a MIDI format. Some early music clips were recorded using that format. Most notably, Windows 95 and Windows 98 include several MIDI files useful in testing a PC's sound capabilities.

The original PC sound cards represented sounds with 8 bits of data. This did not give the best sound representation. Sound cards soon evolved to 16-bit, 32-bit, 64-bit, and 128-bit capabilities. CD quality sound requires a minimum of 16 bits. The 128-bit sound cards are capable of studio quality sound—three-dimensional sound, if used with four speakers—and can synthetically reproduce 128 different multitimbre sounds. Special sound effects, such as reverberation, are also possible.

The original sound cards were ISA bus cards, but newer cards use the PCI bus. Typically, they have input jacks for microphone input, auxiliary input, and audio input that permit recording sounds at sampling rates varying from 5 kHz to 48 kHz. Output jacks are provided for line output, rear speaker output (on three-dimensional soundcards), and amplified output. Often, these cards support joystick ports and MIDI ports for games. Newer sound cards support digital audio format encoding and playing MP3 files, providing 5.1-surround sound, and Dolby® Digital 5.1 audio supporting digitally mastered DVDs. These cards connect to two, four, and five speakers. They decode and play Dolby® Digital 5.1 audio to provide 5.1-surround sound in movies, games, and music without the need for a Dolby® Digital 5.1 receiver. See Figure 1–16.

Figure 1–16 Digital sound card with stereo and mono sound plugs (in inset).

Dolby® Digital 5.1 audio, which is also called AC-3, is an audio encoding technique that compresses as many as six channels of digital surround sound into a single bitstream, reducing CD storage space. When decoded, Dolby® Digital 5.1 audio produces a maximum of six separate, discrete audio outputs. These outputs are left, center, and right channels located in front, providing precise dialogue positioning; two separate rear channels located behind, delivering ambient sounds; and a subwoofer/effects channel, providing deep bass. A combination of five discrete channels and one subwoofer is called a 5.1 speaker configuration.

LAN Adapters

Almost all business PCs are LAN connected. Many home PCs are networked as well using Ethernet, home wiring, or wireless LAN technologies. A LAN provides an easy mechanism for sharing disk drives and exchanging data between PCs. After people work with a LAN, they rarely want to go back to operating without the LAN. LAN connections bring high-speed Internet connectivity to the home. The bad news with LANs is that, when problems occur, the PC looks like it was frozen using liquid nitrogen. Because the PC's operating system gives high priority to communication activities, it can become locked when the communications software connections disappear. A LAN connection requires a LAN card in the PC, cabling to other PCs with LAN cards, and networking software installed in all interconnected PCs. LAN cards are referred to as Network Interface Cards (NICs). Cable modems and Digital Subscriber Lines (DSL) connect into PCs using Ethernet LAN adapter cards. There were three early PC LANs: Datapoint's ARCnet, the IBM token ring, and the Xerox-Intel-Digital Ethernet. Of these today, Ethernet is dominant and quickly evolving to meet the demand for increased transmission speeds that new applications place upon it. ARCnet has disappeared. A new LAN type, Asynchronous Transfer Mode (ATM), is also emerging for businesses. In the long run, it appears that Ethernet and ATM will become the dominant LAN types. LANs implement the electrical signaling on the LAN wiring and facilitate data transfer between equivalent NICs. Digital Equipment Corporation (now Compaq) marketed Ethernet LANs in 1982. It was one of the first LANs to interconnect PCs. In 1987, IBM delivered its token ring LAN. The first token rings were focused on IBM's mainframe computers and PCs. The token ring still holds a significant market niche today. It is moving to higher speeds, but may be displaced by newer technology LAN and telephony NICs in the next few years as ATM technology takes root. Ethernet dominates the PC LAN market and is likely to continue to dominate it. Ethernet uses Unshielded Twisted Pair (UTP) wiring to interconnect PCs. This wire is classified by its electrical characteristics, with different types of wire capable of higher transmission speeds. The initial Ethernet wiring was a coaxial cable bus, which is seldom used any more.

This was not the same coaxial cable used for television, but a version having different electrical characteristics. Television coaxial cable was 75-ohm cable while Ethernet cable was 50-ohm cable. PCs using coaxial cable were connected in a simple bus configuration with coaxial cable running from one PC to another.

UTP cable soon replaced coaxial cable. Twisted pair cable required that each network PC be wired into a hub. The hubs electrically isolated each individual LAN-attached PC from the others so that, if a PC malfunctioned electrically, it did not crash the remaining PCs and the LAN. This improved overall network reliability. Most Ethernet PCs today connect to a switch. Switches provide the same capabilities of a hub and more. They increase Ethernet performance by isolating traffic between PCs from PC traffic.

Ethernet uses a Carrier Sense Multiple Access with Collision Detection (CSMA-CD) media access protocol. Each PC connected to the Ethernet broadcasts as needed. When its broadcasts collide with broadcasts from other stations, the Ethernet NIC detects this by an excess voltage drop on the cable and then computes a new time to attempt a rebroadcast of the corrupted packet. The new time is based upon previous collisions and is randomized within the rebroadcast time window.

UTP wire is classified into categories, with ordinary twisted pair telephone wire being classified as Category-3 wire that is capable of transmission speeds of 10 MB per second. Most Ethernet wiring installations use Category-5 UTP wire, capable of speeds up to 100 MB per second. New Ethernet LAN installations use Category-5 data grade cable (Category 5e or Category 5+) or Category-6 cable, which supports higher speeds. Ethernet is designed to run up to 1 GB per second across Category-5, Category-5e, Category-5+, or Category-6 twisted pair wiring and across fiber optic cables. The general rule is that the higher the speed means the shorter the wires that run between the hub and the PC.

Ethernet PC NICs are ISA 8-bit, ISA 16-bit, and PCI bus cards. The newer Ethernet NIC cards are all PCI bus cards that operate at either 10 MB per second or 100 MB per second and in half-duplex (one way at one time) or full-duplex (two way simultaneous) transmission modes. The new Ethernet cards automatically sense transmission speed and half- or full-duplex transmission capabilities. The token ring network also uses hubs to interconnect the networked PCs.

Similar to Ethernet, the hub isolates each station from the other stations on the token ring network so that PC and NIC malfunctions do not impact the other network stations. The token ring is different from Ethernet and must have hubs to work normally while Ethernet works in a simple bus configuration or in a hub configuration. Furthermore, the token ring hubs must be configured as a closed loop to form a ring and function properly. In the token ring token-passing protocol or Medium Access Control (MAC) operation, a token frame circulates from station to station. When a station has data to transmit, it marks the token frame as busy and appends data to the frame. The frame then circulates around the token ring; the destination station copies the data from the frame as it passes. If the data is copied successfully, the receiving station signals success by setting bits at the end of the frame. As the frame again passes the transmitting station, the transmitting station removes it from the ring and then reissues a free token so that succeeding stations may use it to transmit data they have.

Token ring networks operate at 4, 16, or 100 MB per second and will operate soon at 155 MB per second. The NIC cards have ISA 8-bit, ISA 16-bit, and PCI bus interfaces. IBM specifies token ring cabling as types, with the preferred token ring cabling being Type-1 or Type-2. The data-carrying pairs in these cables are two shielded twisted pairs. IBM Type-3 is equivalent to Category-3 UTP cable. Other token ring manufacturers use the Category-3 and Category-5 UTP cable equivalent to that used for Ethernet.

ATM NICs are beginning to emerge. The ATM technology promises to integrate LAN functionality and video telephony effectively into a single network connection. ATM has switches to switch data between interconnected PCs like a LAN, as well as between interconnected Wide Area Network (WAN) switches like telephony. ATM NICs transmit data at 25 MB per second, 155 MB per second, and 622 MB per second across Category-5, Category-5e, Category-5+, or Category-6 (when finalized) twisted pair wiring and fiber optic cable connections. ATM NICs interface to the PC through the PCI bus. Windows 98 comes with driver software and other software supporting ATM.

Modems

Dialup networking using modems provides Internet connectivity for many home PCs. A modem is basically a telephone for a computer. Modems modulate and demodulate digital data, converting it to analog voice-grade (0 Hz to 4,000 Hz) signals that travel across telephone channels. Modems are specified by their signaling technology, which in turn determines their maximum transmission speed. Table 1–5 lists the signaling specifications and related modem maximum transmission speed.

Table 1–5 Modem Transmission Speed versus Signaling Technology

Modem Transmission Speed	Signaling Specification
300 bits per second (bps)	WE 103/113 (WE—Western Electric)
1,200 bps	CCITT V.22; CCITT V.22bis; Bell 212A (most used in United States)
2,400 bps	CCITT V.22bis
4,800 bps	CCITT V.32
9,600 bps	CCITT V.32
7,200 bps to 14,400 bps	CCITT V.32bis
28,800 bps	CCITT V.FAST
33,600 bps	CCITT V.34; CCITT V.34 +
33,600 bps up and 56,000 (really about 53,000 bps) bps down	V.90 or K-Flex—USR-X2
56,000 bps both up and down	V.92

The speeds listed are the maximum theoretical speeds. Speeds of 28,800 bps and above are sometimes attained across telephone circuits. An excellent connection across a dialup circuit may reach a speed of 49,000 to 53,000 bps.

Modems can be internal or external. When a modem is an external device, it connects to the PC using a serial port conforming to the Electronic Industries Alliance (EIA) 232D specification (RS-232 interface) or through a USB port connection. Typical PCs have 9-pin connectors for their serial ports while modems use 25-pin connectors. This necessitates a 9-pin to 25-pin connector cable. Each wire in the cable has a specific function on controlling data transmission across the cable. For example, pin 2 transmits data while pin 3 receives data in the 25-pin modem connector. This is reversed for the 9-pin PC connector. Most all external modems now use the USB to connect into the PC. See Figure 1–17.

Figure 1–17 USB modem front and rear views.

The modem behaves as though there were a cable when it is used. Modems are sophisticated microprocessor-controlled systems in themselves. They perform not only the modulation/demodulation of the data signal, but they also perform data compression and flow control handshaking with the PC and the remote modem. Data compression specifications for modems are listed in Table 1–6.

Table 1–6 Modem Data Compression

Compression Specification	Error Detection Compression	Remarks
CCITT V.42bis	Error detection and correction Data compression up to 4:1	Little compression and speed increase for compressed files, such as ARC, ZIP, and LZH.
		Some compression and speed increase for binary files, such as EXE, COM, DLL, etc.
		Maximum compression and speed increase for text and tabular files.
		Transmission speed can increase as much as 400 percent above modem speed.
CCITT V.42	Error detection and correction	Error correction only. Uses synchronous transmission to increase effective data rate to as much as 120 percent of the rated modem speed.
MNP Class 5	Error detection and correction Data compression up to 2:1	Similar to V.42bis with less effective data compression. Transmission speed can increase as much as 200 percent above modem speed.
MNP Class 4	Error detection and correction	This protocol includes adaptive packet sizing and data optimization, producing improved data transfer speeds. Maximum improvement on clear telephone lines is 120 percent.
MNP Class 3	Error detection and correction	Uses full-duplex synchronous transmission to increase effective data rate. Maximum transmission speed increase is about 108 percent.
MNP Class 2	Error detection and correction	Uses full-duplex asynchronous transmission to increase data rate. Maximum transmission speed increase is about 84 percent of modem speed.

The flow control handshaking between modems and PCs should always be set to hardware handshaking or Request To Send/Clear To Send (RTS/CTS) handshaking. The modem-to-modem handshaking is software controlled. An example of software handshaking is XON/XOFF handshaking, which is not used for PC-to-modem flow control.

Modems interface to the telephone circuit using the standard Registered Jack (RJ)-11 telephone jack. Typically, each modem has two jacks, permitting the phone line to be connected to the modem and then a phone. One jack is marked line, and the other is marked phone for those connections, respectively. Bad things happen when the phone jack is connected into the line and the line jack is connected to the phone.

The modem card interface in the PC was typically an ISA bus connection, but plug-and-play internal modems plug into the PCI bus. ISA bus connections could be 8-bit or 16-bit connectors because modems are relatively slow devices compared to the other PC peripherals. Some ISA bus modems were plug-and-play compatible, but such ISA bus modems more often than not create installation and configuration problems.

Mouse

The mouse is the Windows pointing device of preference for most PCs. It is a rubber ball that rotates sensors on two right-angle axes. In this manner, the mouse movement is translated into vertical and horizontal pointer movement on the PC's display screen. A mouse is connected to the PC using a 9-pin serial port or through a PS/2 mouse port. Using a PS/2 interface with its small form factor for the mouse frees up the limited serial ports for other uses. Different driver software is required for each type of connection. Windows 9x and Windows NT come with all the needed serial and PS/2 mouse driver software.

A PC mouse has two or three buttons. The left mouse button is the most used. It performs all the selecting and dragging operations with a single click, click-hold, or double-click. The right mouse button expands the mouse functionality to perform specific operations. The middle button expands functionality in certain cases and can also accommodate left-handed usage.

The mouse has been revamped in several different configurations. There is the upside down mouse or trackball. In this case the user's thumb moves the ball and not the entire mouse. Trackballs are supposed to be more reliable because dirt from a mouse pad is not sucked into the movement-sensing mechanics. Of course, thumbs are greasy and sweaty, and dirt can fall down into the trackball mechanism. The trackball is formed to fit a hand. They have several strategically placed buttons to make clicking options easy. Some trackball buttons are configured to provide double-clicks automatically. This can be as troublesome as it can be helpful.

More interesting is the hand-held mouse. It can be used at a distance from the PC. It is held in the hand and not on any pad. Movement of the hand and arm is sensed by the mouse and translated into pointer movement on the PC's display screen. A simple flick of the wrist in this case moves the screen pointer. It also has buttons for selecting items and performing drag-and-drop operations.

Newer pointing devices include glide pads, wheel mice, cordless mice, and optical mice. Glide pads have a touch-sensitive pad area that serves as the mouse. By moving a finger across the pad, the PC's screen pointer moves. Tapping the pad serves as a right mouse button click, and double-tapping serves as a double-click. A tap and hold performs selecting and dragging an item. Touch pad mice are popular for laptop computers. They can be attached to desktop PCs as well. Several buttons are included on glide pad mice to perform both right and left mouse button functions. See Figure 1–18.

Figure 1–18 Glide pad, optical, cordless ergonomic wheel, standard ball, and original two-button mice (clockwise from top left).

A wheel mouse is a traditional mouse with a wheel mechanism mounted between the right and left mouse buttons. The mouse operates normally until a page is selected using an Internet browser of some other desktop publishing application software. When pointing to the page, the wheel permits scrolling the text up and down the display screen. The wheel is rolled to scroll down or up pages of information displayed on the PC monitor. This is very convenient if you work with large text documents or surf the Internet. Wheel mice can be Microsoft compatible, or they can require added software to activate the wheel scrolling function. Some wheel mice have an ergonomic shape that more precisely fits the hand with a fourth mouse button that is activated by the thumb. Most mice today have a wheel function.

Cordless mice carry the wheel function one step further. They transmit mouse movements and button clicks across a low power Radio Frequency (RF) connection to a base unit plugged into the PC. New optical mice have no mouse ball and require no special optical surface to function. They literally operate on any available surface (except water).

Mice connect to the PC using the PS/2 mini-DIN connector port, a USB connection, or through the tried-and-true 9-pin serial port.

Keyboard

The keyboard remains the primary input mechanism for the PC. In the not too distant future, direct voice input devices may displace it. This will not be a total replacement, however, for many more years. Many styles of keyboards are available. They can be broken down into 84-key keyboards like those delivered with the first PC or into 101-key keyboards like those delivered with the PC AT.

Most keyboards today have 104 keys. These are a variation on the 101-key keyboard with three special keys assigned to Windows functions. See Figure 1–19.

Figure 1–19 Wireless Windows 105-key ergonomic keyboard with 12 special function keys.

Important in keyboard layout is the placement and size of the ENTER and the BACKSPACE keys. In my case, these keys get the most use. A small backspace key means lots of mistakes because I tend to hit two keys at one time when they are small. The keys are laid out in a standard QWERTY arrangement with 12 function keys (F1 through F12) across the top of the keyboard. The cursor movement keys (this is somewhat different from the mouse pointer, even though in some cases they perform identical item selection functions) are an inverted "T" arrangement to the immediate right of the main typing area. Above that are the other cursor control keys, including INSERT, DELETE, HOME, END, PAGE UP, and PAGE DOWN. To the far right is a numeric keypad area that emulates an adding machine keyboard, but not a telephone keypad. Adding machines have the low numbers on the bottom of the numeric pad while telephones have them at the top. See Figure 1–20.

Figure 1–20 Keyboard with built-in trackball.

Many laptop keyboards have built-in touch pads to provide mouse functions. Other laptops use buttons (eraser heads) centered in the keyboard or trackballs for their mouse interface. These features, while convenient in a laptop, are really gimmicks that are of little effective use for other PC keyboards.

When a trackball or touch pad feature is installed in a keyboard, it is connected to the built-in keyboard connector and a serial connector on the PC. The keyboard connector can be the older PC/XT/AT style DIN plug or the newer and much smaller PS/2 plug.

If a keyboard breaks, there is no effective repair. In the best scenario, broken keys can be replaced with good keys from another broken keyboard.

Keyboards have evolved to an ergonomic layout with the keys split down the middle. The keys are sloped upward toward the split providing a more natural resting place for your hands. Some keyboards are wireless keyboards that connect to the PC in a fashion similar to wireless mice.

Video

Three components make up the display system: the monitor, the video cable, and a display controller. The video adapter card (display controller) and the monitor determine PC video capabilities. They work in conjunction with each other. The monitor must be capable of producing the image output of the PC video card. Monitors vary in capabilities as well as video cards. The trend is to produce higher resolution (more pixels—dots—spots) images that have more colors. These images then look closer to photographs and movies.

Monitor

The monitor or display is our window into the PC. Through it we see the information inside the PC. Displays have different resolutions or levels of visibility. This is expressed in the number of displayable dots (referred to as "pixels" for "picture elements"), dots per inch (DPI), or spots per inch (SPI). The more dots means the better the image. Displays vary from 320 by 200 resolution to 2,048 by 1,536 resolution and higher. Most monitors are multiscan or multisynch monitors supporting a range of display resolutions. Display clarity also depends upon the dot pitch (from .21 mm to .31 mm) and the number of colors (or gray-scale levels) displayed.

The following is display terminology:

• Monochrome display—A one-color green, amber, or white-on-black background display.

• Monographic display—A single color that displays text and graphics.

• Display—The device producing the image. It may be a Cathode Ray Tube (CRT), Liquid Crystal Display (LCD), or gas plasma display.

• Refresh Rate—Measured in Hz. It is how frequently your monitor redraws its screen—the higher the refresh rate, the better.

• Interlaced—A technique used by monitors to produce higher resolution at lower costs. The actual monitor will only draw the odd horizontal lines on the screen in one cycle and then the even horizontal lines in the next cycle.

• Noninterlaced—A technique used by monitors where all the horizontal lines are redrawn every cycle.

• Monitor—The display and supporting electronics. Monitor and display are synonymous.

• Red, Green, Blue (RGB)—The primary colors forming a color display. This is used to identify the Color Graphics Adapter (CGA) monitor digital interface. Monochrome and monographic monitors used a TTL interface.

• Analog RGB—A VGA monitor interface producing an image with more colors and greater resolution.

Raster and vector graphics are display techniques for creating images. Vector displays draw the images on the screen while raster displays create the images from dots scanned on the display screen. PC displays are raster graphics displays. The original PC monitor was monochrome or CGA with at least 24 useable lines and 80 columns of text. The original PC display was either a monochrome display for text or a CGA display. Today, virtually all PCs use a VGA color display. Monochrome displays had a high persistence phosphor that left a bright green spot on the display after the monitor was turned off. The display resolution was 720 by 350 dots. They could not display graphics, only text characters. This was soon changed by an aftermarket product, the Hercules Graphics Adapter, often called the monographic adapter. This could display graphics and text on a monochrome monitor.

The CGA could display 320 by 200 dots. The resolution here was about half that of a monochrome display. The colors presented were limited to four colors. With the AT came the Enhanced Graphics Adapter (EGA). Color was now beginning to provide the resolution of a monochrome display. The EGA display could project 640 by 350 dots using 16 colors. The EGA's higher resolution permits it to display up to 43 lines of text on the screen.

With the announcement of the PS/2 in 1987 came the VGA display. It could display 640 by 480 dots in 64 colors. At first, these displays were expensive, but, by 1990, the price had dropped to a very competitive level. See Figure 1–21 and Figure 1–22 for display resolution comparisons.

Figure 1–21 Display image with 1024 by 768 resolution.

Figure 1–22 Display image with 640 by 480 resolution.

Monitors are commonly CRT displays capable of displaying 2,048 by 1536 resolution with dot pitches around .22 mm to .28 mm. Very high-resolution monitors are made for CAD workstations and graphic designers.

PC CRT monitors vary in size from 14 inches diagonal to 29 inches diagonal.

At one time, Gateway made a combination TV and PC with a 35-inch monitor. The large monitor had low (800 by 600) resolution and a big dot pitch. Their interface to the video graphics card was a 9-pin analog RGB interface. Some monitors can connect to PCs using USB connections.

Images are constructed on the CRT screen by an electron beam that is scanned across the screen and switched on and off during the scanning. The electron beam is scanned across special color phosphors to create color images on the CRT screen.

Newer flat panel displays are becoming cost-effective. The new LCD or Thin Film Transistor (TFT) flat panels have a very crisp image because their pixels are more precisely formed. They use horizontal and vertical connections to illuminate precisely a single pixel on the screen. They come in several sizes including:

15-inch	1,024 by 768 resolution	$400 to $600
17-inch	1,280 by 1,024 resolution	$900 to $1,500
18-inch	1,280 by 1,024 resolution	$1,300 to $3,400
20-inch	1,600 by 1,200 resolution	$2,500 to $3,900
21-inch	1,600 by 1,200 resolution	$5,500 and up

As you can see, flat panel prices vary dramatically depending upon size. The 15-inch flat panels can cost around $600 while a 21-inch model runs as much as $5,500 or more. See Figure 1–23. Within the next several years, virtually all monitors will be flat panel displays. Some flat panel monitors interface to the PC with the standard analog RGB 9-pin connector. Others require a digital display connection.

Figure 1–23 15-inch flat panel monitor.

Flat panel displays use Cold Cathode Fluorescent (CCF) lamps for backlighting. These lamps lose brightness during their first few hundred hours of operation. After that, the rate of brightness loss tapers off. Lamp lifetime is determined by lamp current, gas pressure, duty cycles, and other factors. A display is considered to be at end of life when the lamps produce only 50 percent of their original brightness. At end of life, a flat panel does not go dark. They remain about 50 percent brighter than conventional CRTs. The estimated time for a flat panel to reach 50 percent brightness is around 20,000 to 30,000 POH or 2 years and 3 months and 14 days if used 24 hours a day and 7 days a week. Dimming features and a power save shutdown after periods of inactivity extends flat panel end of life by several years.

Monitor safety is an important area. Monitors contain high voltages and consequently should be treated with respect. It is not a good idea to disassemble a monitor and power it on because of the danger of electrical shock. Monitors and water definitely do not mix. Some hospital employees playing with a Uzi water pistol one Friday accidentally squirted a monitor that promptly died in flames. It is a wonder that no one was electrically shocked.

Display Controller

The display controller drives the monitor. The display must be matched with the correct controller to produce the proper resolutions.

If we were to use a display that had only 320 by 200 resolution with a controller that was capable of 1,024 by 768 resolution, we could only display 320 by 200 resolution. Most display controllers today have onboard video coprocessors that speed up screen refreshes.

The industry moved from VGA display controllers to the next level called Super VGA (SVGA). SVGA provided a display of 800 by 600 dots and 64 colors. In 1990, IBM announced the next level display controller, the Extended Graphics Array (XGA). Its resolution was 1,024 by 768 dots and 256 colors. By 1992, most SVGA adapters provided a display mode with that resolution. This required so much processing to put information on the screen that the display was beginning to slow.

The speed up of the display comes with the latest VGA video coprocessor and a special AGP bus connection. This evolved from earlier VL-Bus cards. They perform the display processing and speed up the screen transfer rate.

All video cards have display RAM holding the video information we see on the screen. The video display information is first written to the card using a PC video memory-swapping area. The more memory on the display card means the more colors and dots it can display. SVGA and XGA displays require 512 KB video RAM. Newer three-dimensional AGP display cards use 4 MB RAM, but work much better with 8 MB or 16 MB. Most flat panel and laptop displays provide XGA resolution. See Table 1–7 for a monitor and controller feature comparison.

Table 1–7 Display Controller Summary

Display Controller Type	Resolution	Colors	Monitor Interface	Connector	Monitor Scan Rate
Monochrome	720 by 350	2	TTL	9-pin female	18.4 KHz
Monographic	720 by 350	2	TTL	9-pin female	18.4 KHz
CGA	320 by 200	4 from palett (choice) of 16 colors e	RGB	9-pin female	15.7 KHz
EGA	640 by 350	16	RGB	9-pin female	21.8 KHz
VGA	320 by 200 640 by 480	256 (Standard VGA with 320 by 200 resolution) 16 (Standard VGA with 640 by 480 resolution)	Analog RGB	15-pin high- density female	35 KHz
SVGA	800 by 600	256	Analog RGB	15-pin high- density female	50 to 70+ KHz for noninterlaced
XGA	1,024 by 768	256	Analog RGB	15-pin high- density female	70+ KHz for noninterlaced
Super XGA(SXGA)	1,280 by 1,024 and higher	256 colors to 32-bit color (multimillions)	Analog RGB	15-pin high- density female	60 KHz and higher
AGP Adapters	1,280 by 1,024 to 2,560 by 1,024, and others	32-bit color (multimillions)	Analog RGB or Digital	15-pin high- density female or 28-pin DVI-I	60 KHz and higher

Display controllers are providing more onboard capabilities to enhance images. The movement is toward higher resolutions with more colors to produce three-dimensional visual effects. They employ onboard graphics processors (Graphics Processing Unit [GPU]) coupled with high-speed AGP bus transfers to speed up display refresh. Newer controllers provide a digital flat panel monitor output (Display Visual Interface [DVI-I]) connector. See Figure 1–24.

Figure 1–24 ATI dual monitor graphics card with VGA and DVI-I connectors and DVI-I to VGA adapter.

New display controllers provide support for two monitors or are aimed at video and other multimedia applications. The dual monitor displays make both displays into a single desktop operating area for Windows applications. This permits viewing several applications simultaneously, for example, writing this book on one monitor and browsing the Internet for information on the other monitor. Windows can support dual displays using two display cards or a single dual-head display card. Multimedia display cards support three-dimensional graphics and watching TV on your PC, capturing and editing MPEG-2 video, playing DVDs, and using big-screen TV monitors. The newest display controllers are fast becoming the heart of multimedia home entertainment systems. See Figure 1–25.

Figure 1–25 Multimedia PC home entertainment system with cable TV guide and CNN weather.

Printers

PCs today use several different printer technologies. These vary from impact printing, to color inkjet printers, to laser printers, to color laser printers. The market is moving to provide all PCs with high-speed affordable color printing capabilities.

The oldest printers were dot matrix impact printers. This type of printer formed images from small hammers hitting a printer ribbon to deposit ink on a piece of paper. These impact printers are now disappearing, but they remain the only printer type able to produce multipart forms. However, with laser printers becoming cheaper and faster, it is just as easy to print a form two or three times as it is to print on multiple forms simultaneously by impact. Dot matrix printers can produce color images by using multicolored ribbon. They do not effectively print transparency film.

Most low-cost printers are color inkjet printers. Normal inkjet printers use a black ink cartridge and a three-color ink cartridge. Higher quality ink jet printers use black and six colors of ink to produce images. They print by spitting drops of ink at the paper. The ink drops vary in size to produce images that vary from 120 by 120 dots per inch to 720 by 2,880 dots per inch. The ink deposited upon the paper dries to produce the printed image. Inkjet printers can print on plain paper, high-density paper for excellent image reproduction, and special transparency film for presentations.

Humans can discern a maximum resolution of 600 dots per inch. Anything more than that is not really distinguishable by the human eye. The goal for high-resolution printers is to print pictures with photographic quality. Having a relatively low 360 DPI resolution image print at a higher 2,880 DPI resolution does not noticeably improve image quality because your original image has only 360 dots per inch. However, printing a high-resolution image (600 DPI) at high-resolution print quality (720 by 720 DPI) provides an excellent printed image.

Laser printers use xerographic printing to produce black and white images on plain paper. Some laser printers print at high speed on both sides of the paper while others provide good high-resolution inexpensive black and white image printing. See Figure 1–26.

Figure 1–26 Inexpensive laser printer.

This process means that laser printers are page printers, not line printers. Dot matrix ribbon and inkjet printers are line printers that print a single line at a time. When printing to a laser printer, the printer does not start printing until an entire page of data has been sent to the printer. In contrast, dot matrix and inkjet printers print each line as it is received from the PC. To see this, just do Print Screen to a laser printer several times. Laser printer page printing often confuses people. They send a printout to the laser printer and nothing happens. They again send the printout to the laser printer, only to discover that they have printed it twice and run both printouts together.

Making sure that your software sends a Form Feed character to the laser printer at the end of each document printed solves this problem. The Form Feed character causes the laser printer to print all data it has in its buffer.

Color laser printers use multicolored dyes to produce color printouts on plain paper. They employ a variety of printing technologies to produce the images. Some color laser printers use xerographic toner, and others use thermal wax to produce images. See Figure 1–27. These printers are becoming much cheaper in price and consequently much more prevalent.

Figure 1–27 Thermal wax laser color printer.

Printers interface to the PC using the parallel port. Some new printers are directly attached to a network to permit sharing between multiple workstations. Some printers use infrared links, and others use USB ports to connect to PCs.

Scanners

Scanners scan paper and photographic images and convert them to digital images and text. Photos scanned in are processed by PC software to enhance image quality. Computer software can be sophisticated or relatively simple when handling images. Special optical character recognition software converts a scanned image into a formatted text file.

Several types of scanners are popular. These include:

• Flatbed scanners—These scanners operate like a standard copy machine. The document to be scanned is placed on a flat glass panel, and a light is run under it. They can scan single sheets, photos, or books. They're usually the most popular choice today. See Figure 1–28.

  Figure 1–28 Flat bed scanner with automatic document feeder.

• Sheet-fed scanners—These scanners handle full-size paper fed through a slot. In this case, the paper moves and not the light. Until recently, sheet-fed scanners cost less than flatbed scanners, but prices are almost the same today.

• Specialty scanners—These scanners come in a variety of sizes and shapes. They can be handheld or sheet-fed models modified for a specific task or ease of use. Some are built into keyboards and others into PCs. This category includes dedicated devices designed to handle nothing but business cards or slides.

• Multifunction units—This is a combination scanner, printer, and fax in one space-saving unit.

All scanners scan color images although some early scanners only scanned black and white images. They all have a set of specific scanning resolutions that they can produce. The specialty scanners and multifunction scanners are aimed at specific tasks, like scanning business cards or family photographs. These are typically sheet-fed scanners. Document scanners are mostly flatbed scanners. Some sheet-fed and flatbed scanners scan multiple sheets automatically. Hand-held scanners are best for mobile applications. A few scanners were even designed to scan multidimensional images. They used a camera mounted up away from the image placement area. Scanners most often attach to the PC using SCSI adapters or USB connections.

Web (Video) Camera

Video cameras are used to capture single frame images or continuous video streams for the PC. They help turn any PC into a video telephone with the appropriate communications and software. They are also capable of capturing single frame images for transmitting with email and other communications. See Figure 1–29 and Figure 1–30.

Figure 1–29 Pete from Web (video) camera.

Figure 1–30 USB Web camera.

These are simple Charge-Coupled Device (CCD) imagers with varying resolution and color capabilities. The best Web cameras capture frames at 30 frames per second, but capture rate varies with resolution. Higher resolutions have slower video capture rates. Some Web cameras double as still-image cameras that go anywhere for snapshots. Older Web cameras connected to the PC through the parallel port or a special video capture card. Most current Web cameras connect through a USB connection. Web (video) cameras have become part of almost every PC system.

Still Cameras

PC systems have enhanced photography. Digital cameras are challenging film-based cameras as the most common household camera. A digital camera that produces a megapixel image provides all the capabilities needed to make acceptable pictures for the average photographer. The photographs in the first revision of this book were taken with a Sony Mavica camera that had a good lens and a maximum resolution of 1,024 by 768 XGA. They were OK pictures, but lacked some resolution. A Nikon CoolPix 990 camera with a maximum resolution of 2,048 by 1,536 (3.34 megapixels) shot the pictures for this revision. The new pictures contain much more detail than the original version pictures.

Most digital still-image cameras interface to the PC through the USB. Cameras use a variety of memory types as digital film. Sony cameras use Memory Sticks that are expensive. Other cameras use microdrives, CompactFlash (CF), Smart Media, Memory Stick, and floppy disk memory. See Figure 1–31.

Figure 1–31 CF and Smart Media digital camera film.

Inexpensive USB devices connect the CF and Smart Media camera film directly into the PC using the USB. The pictures can be accessed and transferred to the PC as though they reside on a removable disk drive. The Windows Explorer program transfers images when they are dragged from the digital filmcard and dropped into a folder on the PC's fixed disk drive. See Figure 1–32.

Figure 1–32 Standard (left) and USB compliant (right) CF cards, USB interface devices, and PCMCIA interface device (center).

Microphone and Speakers

Sound capabilities are an important part of every PC today. Soon, they will replace the audio systems used in most homes because the PC provides the capability to produce CD-quality surround sound with precise control of the music selections played. To provide these audio capabilities, the PC uses a good sound card attached to speakers. These speakers are stereo high-frequency speakers and a subwoofer speaker to produce the bass sounds. The PC speakers are self-powered. They do not get their power from the PC sound card, but rather from powered amplifiers built into the speakers themselves. Figure 1–33 shows powered PC speakers with the stereo minijack that connects into the soundcard. Figure 1–34 shows a PC powered subwoofer speaker that produces deep bass sounds. The speakers plug into the stereo outputs from the soundcard.

Figure 1–33 Powered PC speakers with stereo minijack.

Figure 1–34 Powered PC subwoofer speaker.

Some sound cards have a separate output for the subwoofer speaker while others have outputs for four-speaker surround sound, and still others support the new Dolby 5.1 surround sound. The audio quality rivals that of an expensive stereo system for most people. Only the most discerning audiophile would detect the difference between a PC-driven stereo system and a receiver-driven system. The only real advantage of a conventional system over a PC-driven sound system is that the conventional system connects to a tape deck, Frequency Modulation (FM) radio receivers, and a multitude of other audio components. PC systems can connect to such components as well, but they typically have limited output jacks on their sound card. It is almost easier to connect them to a conventional stereo receiver and connect that receiver to the other audio components than to attempt to connect the PC to the audio components directly.

Microphones permit sound input to the PC. The standard run-of-the-mill microphones provided with most soundcards do not provide sufficient quality for voice recognition and for broadcast audio use. Sound cards work with high-quality microphones. Such microphones reduce background noise and produce studio-quality sound. We used a high-quality microphone to record some audio material for our radio show that was stored in an MP3 compressed audio format, sent to a Diamond RIO MP3 player, and from there input to the radio station's control panel for broadcast. This worked quite well and provided near studio-quality sound. Other microphones are directional and use the USB to connect to the PC. See Figure 1–35.

Figure 1–35 USB directional microphone.

MP3 is a sound file storage format. Music and sound files are stored on a computer disk in such a way that the file size is relatively small, but the recording sounds near perfect. MP3 files typically have file names with an MP3 extension.