PC Component Overview

 

Case and Power Supply

 

Computer cases come in many different sizes and styles. Desktop units usually have two to three 51/4-inch drive bays and two 31/2-inch drive bays. Mini tower cases have the same general configuration as the desktop cases but are arranged sideways so the case stands on one side rather than on the bottom. Full tower cases are extensions of mini tower cases. They usually contain up to seven 51/4inch drive bays and two to four 31/2-inch bays.

 

Power supplies are most often found mounted to the rear of the case. They can range from 150 watts to more than 250 watts. The size of the power supply depends on the anticipated use. If you have multiple devices on your system, you will need a larger-than-normal power supply. Most power supplies have output voltages of 5 and 12 V dc.

 

Power supplies have fans that move air across the components to keep them cool. A common failure point on power supplies is the fan. When most fans begin to fail, they make an audible noise. This is the first indication of a problem. The power supply may continue to function, but it will usually quit altogether in less than two months. Exactly how long it will continue to operate is dependent upon the amount of time the unit is powered on each day. When the fan fails, the rest of the internal components overheat and break down. The best course of action is to replace the power supply when the fan begins to fail.

 

Power supplies connect to the building electricity via a three-prong connector on the rear of the PC case. Generally, you may also find a small switch on the power supply that enables you to select the input voltage.

 

You can sometimes prolong the life of a failing power supply fan by drilling a very small hole in the center of the fan guard and applying a small drop of oil. This will lubricate the contact point between the fan shaft and the power supply case. If your fan does not use the case as a support for the fan shaft, taking this step will have no effect.

 

Motherboards

 

The motherboard or system board is usually the largest board in the computer. It normally contains the processor, coprocessor, memory chips and expansion slots as well as a host of other integrated components. Some motherboards found in low profile cases do not have expansion slots. This type of board uses a special slot that accepts a board that usually has three expansion slots on it. The expansion boards will be installed parallel to the motherboard instead of perpendicular as in the generic motherboard. This type of board will also have integrated devices such as video controllers, serial and parallel ports, and hard and floppy drive controllers.

 

Basic Components and System Designs

 

History of the PC

 

The first mass-produced personal computer was the Altair 8800. It came out in 1975 and was produced MITS. The computer used an 8-bit Intel 8080 CPU and had 256 bytes of memory. This computer did not have any peripheral devices such as a monitor, keyboard or disk drives. The computer used a version of BASIC, which was written by Bill Gates.

 

Within a short period of time, several other companies began producing personal computers. These computers utilized an operating system called CP/M, produced by Digital Research. Most of these computers were used by hobbyists and were not seen as tools for business.

 

In 1980, IBM decided to enter the personal computer market. IBM did not want to make its own chips or software for its new line of PCs, so it purchased CPUs from Intel and an operating system from a newly formed company called Microsoft. The first IBM PC came out in August 1981 with just 64K of RAM and a 160K floppy disk drive. It was thought that the only significant use for this machine would be for playing games. IBM made the PC an open system that gave other hardware and software manufacturers the ability to make products for the PC. This created a huge market and allowed other vendors to create clones.

 

IBM introduced the PC/XT in March 1983. This was the first PC with a hard drive, and it came with MS-DOS 2.0 and an 8088 processor. This new version supported 360K diskettes and a UNIX ­type tree directory structure. The PC/XT quickly moved PCs out of the home and into the office environment.

 

17 months later, IBM came out with the PC/AT. This computer was based on a 286 processor. It supported up to 16MB of RAM and had the ability to run multiple programs at once. This new PC also came with a 1.2MB disk drive, a battery backup clock and MS-DOS 3.0. This version of DOS could run the computer only in real mode, which simulated the 8088-processor operating mode. This allowed backward compatibility, but it did not take full advantage of the new processor.

 

IBM then introduced the PS/2 in 1987. These computers came with 720K and 1.44MB 3.5-inch diskette drives and contained the next generation of processors, the 80386 by Intel. The operating system was MS-DOS 3.3, which supported the new diskette drives. With the introduction of the PS/2, IBM and Microsoft introduced a new operating system, OS/2. It was thought that this new operating system would replace MS-DOS, but it never happened. The first release of OS/2 was able to make use of extended memory and it supported multi­programming, but it was released prior to being thoroughly tested and it contained many bugs. Because the operating system did not catch on like Microsoft wanted, the company dropped it. This caused a split between IBM and Microsoft. Microsoft began concentrating more on its graphical operating system called Windows.

 

The 80386 processor and motherboard systems were released in two different types, the 386DX and the 386SX. The difference between these two systems was the motherboard. The DX system ran on a new 32-bit motherboard, while the SX system ran on a 16-bit 286 motherboard. Both systems had processors that internally were 32-bit, but the SX communicated with the outside world on the 16-bit level.

 

Intel introduced the 486 processor in April 1989. This processor was very similar to the 386, with a few exceptions. These exceptions created dramatic performance improvements. The 486DX processors included an integrated math coprocessor and a small Level 1 cache on the chip.

 

The 486 local bus was dramatically different from that of the 386, resulting in significant increases in bus transfer rates. The 486 referenced data in blocks of up to 16 bytes in size, while the 386 bus sent an address with each memory reference. The result of this burst-mode block transfer scheme was a 50 percent performance increase in the data transfer rate.

 

Because there was a tremendous price difference between the new 486 chips and the top-of-the-line 386 chips, Intel introduced a 486 chip that did not include the integrated math coprocessor. This chip was called the 486SX and was one-third to one-half the price of the 486DX chip.

 

The next chip to be released was the clock-doubled 486 chip, called the 486DX2. This chip doubled the internal clock rate of the processor while allowing it to continue communicating on the outside with its original speed. A clock-tripled chip, the 486DX4, was released next.

 

In March 1993, Intel introduced the Pentium processor. This new processor contained 3.1 million transistors, compared to the 486's 1.2 million. The internal cache size was increased to 16K, and the local bus width was increased from 32 bits to 64 bits. The speed of the bus was also increased to 60 and 66 MHz. The first Pentium processors that were released were 5-volt chips and produced a great deal of heat, which resulted in several heat-related problems.

 

With the release of faster processors, Intel reduced the voltage to 3.3. This dramatically reduced the heat-related problems, and the systems with these new chips improved in stability.

 

The Pentium Pro chip has been optimized for 32-bit applications and does not run 16-bit applications as well as its predecessors. This is why Windows 95 runs faster on a 20200MHz Pentium than on a 200MHz Pentium Pro.

 

The latest improvement in the Intel line of processors is MMX. MMX technology optimizes multimedia performance, increasing the processor's ability to handle the large data streams associated with multimedia programs.

Bus Architectures and Expansion Slots

 

The original PC, which used an 8088 processor, had an 8-bit, bi-directional data bus. This bus had two rows of connectors with 31 pins on each row. When the PC/AT came out, it had a new 16-bit data bus. This bus maintained the original slot with 62 connectors configured in two rows and added a second connector with 36 pins. This enabled the new bus to accept 8-bit expansion cards that were used with the original PC/XT bus. The new 16-bit expansion slots are now referred to as ISA (industry standard architecture) slots.

 

EISA (extended industry standard architecture) slots resemble ISA slots, but there are some important differences. An EISA slot is deeper than an ISA slot to allow it to accept both 16­bit ISA and 32-bit EISA cards. This type of expansion slot dramatically increased the cost of the motherboard, so it really did not catch on as well as the VLB and PCI slots did.

 

VL-Bus (VESA local bus) is a 32-bit expansion slot that will accept cards specifically designed for the slot as well as ISA and 8-bit expansion cards. This type of expansion slot became popular with the release of the 486 processors. This slot was originally created to handle multimedia and to speed large amounts of data through the PC bus.

 

When the PCI (peripheral component interconnect) slot was developed, there was a great deal of discussion as to which was better, the VL-Bus or PCI. PCI eventually won out due to the 64-bit slot available in the Pentium-based systems.

 

PCI slots in 486 systems are 32-bit, and, unlike the VL-Bus slots, will accept only PCI expansion cards. The PCI bus has become the standard on most Pentium and Pentium-compatible systems.

 

The IBM PS/2, originally came with a Micro Channel Bus. This bus contained additional power and ground pins, which allowed the card to draw more power from the motherboard with less impedance. This resulted in less RF interference and improved data integrity.

 

The Micro Channel bus supports three types of cards: 32-bit, 16-bit and 16-bit with video extensions. It also supports multiple bus masters by providing a set of signals that allows expansion cards to act as bus masters. In addition to the video extensions, the Micro Channel bus also contains an audio subsystem feature that can provide high-quality audio capability between devices and output over the system speaker.

 

The Micro Channel bus does not use addressing and configuration switches on expansion cards. It uses a feature called POS (programmable option selection) to configure the expansion cards. When the computer is turned on, it accesses each expansion slot. The expansion cards issue a code when they are accessed. The processor reads the code and compares it to the configuration data stored in the computer nonvolatile memory and then loads that data into the expansion card. While this system was very effective, it did not catch on, and has since been abandoned.

 

RAM Chips

 

With today's operating systems and software, random access memory (RAM) is the key to a properly functioning computer system. Adding RAM to a computer is the easiest and quickest way to upgrade a system. Computer memory comes in a variety of forms. The normal form is a DRAM chip in the form of SIMMs (single in-line memory modules), or DIMMs (dual in-line memory modules).

 

The smallest DRAM chip is called a DIP (dual in-line package). DIPs normally range in size from 16K to 1024K. SIPPs (single in-line pin packages) resemble SIMMs with one exception: They contain a single row of pins on the bottom instead of an edge connector. SIPPs range in size from 256K to 1024K. SIPPs are the least common type of memory module.

 

SIMMs come in both a 30-pin format and a 72-pin format. 30-pin SIMMs range in size from 256K to 16MB. During the era of 386-based computers, 30-pin SIMMS were the most common type of memory module on the market. Today, the most common types of memory module for desktop computers are the 72-pin SIMM (ranging in size from 4 MB to 32MB) or the 168-pin DIMM (16MB to 1 GB).

 

Hard Drives

 

The hard drive first appeared in the IBM PC/XT and stored a whopping 10MB of data. Most people never dreamed they could ever use that much storage space. Today, hard drives can store more than 9GB of data. while most computers on store shelves have at least a 2.1 GB hard drive, a 3.2 GB hard drive is fast becoming the norm.

 

Hard drives of the past used either an ST-506 interface or an ESDI (enhanced small device interface) to transmit data to other parts of the computer. Today's hard drives use either SCSI (small computer systems interface) or IDE (integrated drive electronics) drives.

 

A hard drive consists of several disks, or platters. Data is stored on hard drives in bytes. The bytes are arranged into groups of 512 bytes, which are called sectors. Sectors are grouped together into concentric tracks. Tracks are sometimes referred to as cylinders, but this is a mistake. Cylinders are actually made up of a single track that runs through the platters. Tracks are circles and if you stack circles on top of each other, you will get a cylinder. The number of tracks on each platter is identical to the number of cylinders on the hard drive. This is why manufacturers list information about the number of cylinders and don't usually list any track information.

 

Floppy Drives

 

Floppy drives have been designed in many sizes. The first floppy drive in a PC could hold 160K bytes of data. When IBM introduced the PC/XT, it came with a 360K diskette drive. These were called floppy drives because the diskettes that were used in the drives were very flexible. Eventually, a 1.2MB diskette with this same construction was introduced. Even though the 1.2MB looks identical to the 360K diskette, it is constructed using different materials and stores data in a different way. You may be tempted to format a 360K diskette to 1.2MB, but you will get several bad sectors during the format process. You should always use the appropriate diskette to avoid data loss.

 

In the late 1980s, the 3.5-inch diskette was introduced. This new diskette could hold 720K of data. This diskette also came in a harder case than previous diskettes. A spring-loaded door closed over the opening to the magnetic media when the diskette was removed from the drive. Today these 3.5-inch diskettes can hold up to 2.88MB of data, but the norm is 1.44MB.

 

Diskette drives use MFM to encode data on the disks. This is the same encoding method the first hard drives used. Access times for most floppy drives is greater than 100 milliseconds (ms). This compares to less than 10ms for most new hard drives.

 

Expansion Cards

 

Expansion cards, also called adapters, allow you to add devices to your PC. These devices can range from CD-ROMs to video display devices. Expansion cards vary according to the bus they were designed for. The most common types of expansion card are the 16-bit ISA card or the 64-bit PCI card.

 

Expansion cards plug into slots on the motherboard. Most expansion cards have external connectors to attach external devices to the computer. Below is a list of some of the more common types of expansion cards:

 

Video controllers              Serial ports

Parallel ports              CD-ROM controllers

Hard drive controller cards                       Modems

Network adapter cards              Sound cards

SCSI host adapters              Game port cards

 

Some expansion cards are multifunction cards. These cards combine several controllers onto one card. An example of this would be an input/output (1/0) card that has serial ports, a parallel port, a game port, a hard drive controller and a floppy controller all on a single card. You may find several of these devices integrated on the motherboard.

 

Ports

 

Ports provide a way to attach devices such as printers, mice and modems to your computer. There are two main types of ports on most PCs: Parallel and serial.

 

The parallel port is most commonly used to connect printers to computers. Parallel ports were originally unidirectional; but most today are bidirectional, which allows devices such as scanners and tape devices to be connected. Newer EPPs (enhanced parallel ports) not only support bi-directional data transfer but also support increased data transfer speed.

 

Serial ports, also referred to as com ports or RS-232 ports, support low-to medium-speed bi­directional data transfer. Serial ports are used to connect mice and external modems to the computer. They have also been used to connect printers to computers, but with the development of parallel ports this use has dramatically declined. most serial ports support data transfer rates of up to 115,000 bits per second, but some serial ports can support up to 345,000 bits per second. Serial ports come in two different configurations: 9-pin and 25­pin types.

 

Monitors

 

The first computers designed for home use did not come with monitors. These units came with adapters that connected to television sets. The first monitors that were designed to work with PCs were monochrome. These monitors usually had black backgrounds and displayed text in either amber or green. They provided greater resolution than a television set but that was their only advantage over televisions.

 

The next type of monitor to be introduced was the RGB monitor (also called the CGA monitor). This monitor could display four colors from a 16-color palette with a CGA display adapter or 16 of 64 possible colors with an EGA adapter.

 

Graphics could be displayed to a maximum of 640 x 200 pixels. The input for this type of monitor was digital. The maximum vertical refresh rate of this type of monitor was 200 pixels, so the EGA adapters used an interlacing technique to produce 350 lines and achieve a resolution of 640 x 350 pixels.

 

The EGA (enhanced graphics adapter) monitor could be used with a CGA or an EGA display adapter. When used with an EGA display adapter, it had a resolution of 640 x 350 pixels. These were the last monitors to use a 9-pin D shell connector. This type of monitor was actually an RGB monitor with a higher resolution. As such, it could display 43 lines of text per screen rather than the usual 25. This may have seemed to be a nice improvement but most programs could not support the 43-line mode.

 

The next monitor standard to be introduced was the VGA (video graphics array). This type of monitor provides a resolution of 640 x 480 pixels. The VGA monitor uses an analog RGB input instead of the digital input used by previous monitors. VGA monitors have a color palette of 262,144 colors. This type of monitor uses a 15-pin D shell connector.

 

An improvement of the VGA monitor is the SVGA or super VGA monitor. This monitor can display 1024 x 768 pixels, and some can even display resolutions of 1280 x 1024 pixels. The SVGA has become the standard type of monitor on most PC systems.

 

An important factor to consider when deciding on which monitor to purchase is the dot pitch. Dot pitch is actually the width of the dots the monitor can display. Generally, monitors with smaller dot pitches will produce sharper images.

 

Dot pitch sizes range from .39 to .22. To decide which dot pitch will best suit your needs, you will have to know what resolution you will be using and the size of the monitor screen. Larger monitors can usually have larger dot pitches (such as .31), but for smaller monitors you should try to purchase one with a maximum of .28 dot pitch. If you need a SVGA monitor with a resolution of 1024 x 768 pixels, then you will want to purchase one with a .26 dot pitch.

 

Video Cards

 

The video card, or video display adapter, is a card that controls the computer monitor. In some systems, this adapter is integrated into the motherboard, but in other systems you will find the display adapter in an expansion slot on the motherboard. Today, most video display adapters are SVGA cards. These cards come in various bus designs, from the standard 16-bit ISA to 64-bit PCI configurations. There is also a wide variety of memory configurations on these cards as well.

 

video memory not only helps improve the speed of the video card but also determines the number of colors and the resolutions the card will be capable of displaying. Table 1 outlines the memory requirements of video adapters based on the number of colors and resolution.

 

Screen Pixel Resolutions

 

Color Modes                 640x480              80OX600              1024x768              1280x1024              1600x1200              1920x1440

16-color              153,600                     240,000              393,216              655,360              960,000              1,382,400

256-color              307,200                     480,000              786,432              1,310,720              1,920,000              2,764,800

True-color              614,400                     960,000              1,572,864              2,621,440              3,840,000              5,529,600

 

High-color              1,228,800 1,920,000 3,145,728                   5,242,880              7,680,000              11,059,2OO

 

Table 1: Video memory requirements in bytes for color modes and screen resolutions

 

As Table 1 shows, the memory requirements for different resolutions and colors can become quite steep. For most modern graphics software, you should have a video card with no less than 2MB of video memory.