1.5 Identify the names, purposes, and performance characteristics, of standardized/common peripheral ports, associated cabling, and their connectors. Recognize ports, cabling, and connectors, by sight.
A personal computer (PC) is a computing device made up of many distinct electronic components that all function together in order to accomplish some useful task (such as adding up the numbers in a spreadsheet or helping you write a letter). By this definition, note that we're describing a computer as having many distinct parts that work together. Most computers today are modular. That is, they have components that can be removed and replaced with a component of similar function in order to improve performance. Each component has a very specific function. In this chapter, you will learn about the components that make up a typical PC, what their function is, and how they work together inside the PC.
NOTE
Unless specifically mentioned otherwise, throughout this book the terms PC and computer can be used interchangeably.
The components in most computers include:
* The case
* The power supply
* The motherboard
* The processor /CPU
* Memory
* Storage devices
* The adapter cards
* Display devices
* Ports and cables
As you read this chapter, please keep in mind that many of these parts will be covered in more detail in later chapters. Figure 1.1 shows an example of a typical PC and illustrates how some of these parts fit together.
The Case
A computer case is the enclosure that encases all the components of a computer. All the computer's components mount to the inside of the case-the case is essentially the mounting platform for all the electronic devices that make up the computer. Typically, cases are square or rectangular boxes, usually beige in color (although the current trend is for all-black cases and matching peripherals), and made of steel, aluminum, or plastic. Figure 1.2 shows an example of a typical computer case.
NOTE
To see some examples of many different styles and colors of computer cases, visit www.pimprig.com.
Cases are primarily categorized in two ways: by their physical size (full tower, mini tower, and so on) and by the type of motherboard they are designed for (such as AT, ATX, or Mini-ATX). We'll talk more about motherboard designs in a later chapter. For now, just remember that in addition to their type, cases must also be designed for the motherboard type. You could have two cases with the same physical dimensions and look, but with completely different internal layouts suitable for their motherboards.
Case styles vary in the way they normally sit (vertically or horizontally) as well as the number of device bays they support. A device bay (or bay for short) is a large slot into which an expansion device fits (usually a disk drive of some sort). There are two bay sizes: 5 1/4-inch (typically used for CD-ROM and similar drives) and 3 1/2-inch (used for floppy, Zip, and hard disk drives).
Several common PC case styles are in use today. Let's take a quick look at each of these and how they differ. These styles include:
* Full tower
* Mid tower
* Mini tower
* Midi tower
* Desktop
* Slimline
* Proprietary
NOTE
It is important to note that these are general guidelines. What one manufacturer calls a tower, another may call a mid tower. When you're determining whether a particular case will fit your needs, it is more important to note its physical size and specifications than its labels.
Full Tower
A full tower case is a computer case that stands approximately 20-25 inches tall, has at least five 5 1/4-inch drive bays, and is designed to stand vertically on the floor next to a desk (instead of on the desk). This type of case usually has wheels so you can move it easily when you need to unplug a cable or do other work on the computer. Often, because of its sheer size, it will have stabilizing feet to prevent it from tipping over. Figure 1.3 shows an example of a full tower case.
Full tower cases are often used for server computers because of the number of disk drives a server needs to hold. If a computer you are building or buying needs lots of drives, you may want to look into a full tower case.
Such a case also has a lot of room inside. This space allows components to be separated and provides good airflow around them. People who need many different components inside their computer and need to keep temperatures in check for reliability might also consider a full tower case.
The full tower case has a couple of drawbacks. The most obvious is sheer size. The case's large size makes it awkward to place anywhere but on the floor next to your desk (which may not always be possible). Also, because full towers are the largest type of case, they are usually the most expensive you can buy.
Mid Tower
A mid tower case is a computer case that stands between 16 and 19 inches tall, has at least three 5 1/4-inch drive bays, and is designed to stand vertically either on the floor or on a computer user's desk next to the monitor. This type of case doesn't have quite as much room inside as a full tower case, but it still has significant room for airflow and component layout. And, these cases are less expensive than full tower cases. At the time of this writing (early 2003), the mid tower case is probably the most popular case being sold for computers. Figure 1.4 shows an example of a mid tower case.
About the only drawback to a mid tower case is that it doesn't quite fit well on either the floor or a desk. It's a bit too big for a desk and a bit too small for the floor. But, because it is more convenient, most people make room for the case on their desk.
Mini Tower
A mini tower case is a computer case that stands about 12 to 15 inches tall, has one or two 5 1/4-inch drive bays, and is designed to stand next to a computer monitor. It was designed to keep the small form factor of a desktop case but also keep the look of a tower, which is more visually appealing. Mini towers are often used in low-end or entry-level computer systems to keep the price down. They are the cheapest possible tower-style case you can buy. Figure 1.5 shows an example of a mini tower case.
The main drawback to mini tower cases is their relatively small size. Most components are packed inside these cases with relatively little room for airflow, so the cases tend to be used for computer configurations that don't have many components (housing all-in-one motherboards, for example).
Midi Tower
Midi tower case is a term used to describe a computer case that's between a mid tower and a mini tower in size. The term is used (mostly in Europe) interchangeably with the term mid tower . It's primarily a marketing term, and not really a case type. (This case type has nothing to do with Musical Instrument Digital Interface [MIDI], the technology used to interface computers with digital musical instruments.)
Desktop
A desktop case is designed to lie horizontally, with at least three 5 1/4-inch bays oriented horizontally and the 3 1/2-inch bays oriented vertically. The original IBM PC used this style of case (although the case for the original PC was much bigger). Currently, the dimensions for a typical full size desktop case are about 15 to 17 inches wide and 5 to 7 inches high. Figure 1.6 shows an example of a desktop case.
This case design usually saves floor and desktop space and was the design of choice for corporate America for several years for this reason. However, this case costs about the same as a similarly configured mini tower case and has less internal space. Desktop cases also don't necessarily cool as well as their vertically oriented cousins (and it didn't help that people were putting monitors on top, adding to the internal heat level). For these reasons, sales of desktop systems today are much slower compared to similarly configured mini tower versions.
Slimline
Because desktop space is always at a premium, case designers continually develop new designs that hold the most components in the least amount of space. Toward that end, designers have come up with the slimline case. A slimline computer case usually has only one 5 1/4-inch drive bay, mounted horizontally (or possibly two, side by side). It's designed to take up the least amount of desktop space, and is the smallest standardized form factor. Figure 1.7 shows an example of one type of slimline case.
The only advantage of the slimline case is its small size. However, this small size leads to one major disadvantage: heat. Heat shortens the life of computer components, and due to the small size of slimline cases, they require specialized cooling design (and they still do a poor job of cooling). Even so, sales of slimline cases continue to rise as people try to make their PC as unobtrusive on their desk as their pencil cup.
Proprietary Case Designs
The cases we have listed so far are only some of the styles available. Many PC manufacturers (such as Dell and Gateway) don't use standardized cases, but rather manufacture their motherboards and cases together to keep costs down. This results in what are known as proprietary case designs. A proprietary case is a computer case that is designed to work with only one particular motherboard and set of components and is typically designed for a specific purpose.
Dell's computers are a perfect example of PCs that use proprietary cases. Although Dell's cases could be classified as mid tower or mini tower, they only work with Dell motherboards designed for the particular case and are therefore usually classified as proprietary.
NOTE
You can check out some of Dell's computers at www.dell.com.
Comparison of Case Designs
Now that we've discussed the styles of cases, let's take a quick look at the different designs available. Table 1.1 compares the case designs you have read about in this chapter.
The Power Supply
The computer's components would not be able to operate without power. The device in the computer that provides this power is the power supply (Figure 1.8). A power supply converts 110 volt or 220 volt AC current into the DC voltages that a computer needs to operate. These are +3.3 volts DC, +5 volts DC, -5 volts DC (ground), +12 volts DC, -12 volts DC (ground), and +5 volts DC standby. The 3.3 volts DC and +5 volts DC standby voltages are used only by ATX motherboards, not AT motherboards.
NOTE
You may frequently see volts DC abbreviated as VDC.
WARNING
Power supplies contain transformers and capacitors that carry lethal amounts of current. They are not meant to be serviced. Do not attempt to open them or do any work on them.
Power supplies are rated in watts. A watt is a unit of power. The higher the number, the more power the power supply (and thus your computer) will use. Most computers use power supplies in the 250- to 400-watt range.
Power Supply Connectors
Power supplies use four types of connectors to power the various devices within the computer (Figure 1.9): floppy drive power connectors, AT system connectors, ATX power connectors, and standard peripheral power connectors. Each has a different appearance and way of connecting to the device. Additionally, each type is used for a specific purpose.
Floppy Drive Power Connectors
Floppy drive power connectors are most commonly used to power floppy disk drives and other small form factor devices. This type of connector is smaller and flatter (as shown in Figure 1.10) than any of the other types of power connectors. These connectors are also called Berg connectors. Notice that there are four wires going to this connector. These wires carry the 2 voltages used by the motors and logic circuits: +5VDC (carried on the red wire) and +12VDC (carried on the yellow wire) plus 2 black ground wires.
AT System Connectors
The next type of power connector is called the AT system connector. There are two 6-wire connectors, labeled P8 and P9 (as shown in Figure 1.11). They connect to an AT-only motherboard and deliver the power that feeds the electronic components on it. These connectors have small tabs on them that interlock with tabs on the power connector on the motherboard. If there are two connectors, you must install them in the correct fashion. To do this (on most systems), place the connectors side by side with their black wires together, and then push the connectors onto the receptacle on the motherboard.
TIP
Although it's easy to remove this type of connector from the motherboard, the tabs on the connector make it difficult to reinstall it. Here's a hint: Place the connector at a right angle to the motherboard's connector, interlocking the tabs in their correct positions. Then tilt the connector to the vertical position. The connector will slide into place easily.
It is important to note that only computers with AT and baby AT motherboards use this type of power connector. Most computers today use the ATX power connector to provide power to the motherboard.
ATX Power Connector
The ATX system connector (also known as the ATX motherboard power connector) feeds an ATX motherboard. It provides the six voltages required, plus it delivers them all through one connector: a single 20-pin connector. This connector is much easier to work with than the dual connectors of the AT power supply. Figure 1.12 shows an example of an ATX system connector.
Standard Peripheral Power Connector
The standard peripheral power connector is generally used to power different types of internal disk drives. This type of connector is also called a Molex connector. Figure 1.13 shows an example of a standard peripheral power connector. This power connector, though larger than the floppy drive power connector, uses the same wiring color code scheme as the floppy drive connector.
The Motherboard
The spine of the computer is the motherboard, otherwise known as the system board (and less commonly referred to as the planar board). This is the olive green or brown circuit board that lines the bottom of the computer. It is the most important component in the computer because it connects all the other components of a PC together. Figure 1.14 shows a typical PC system board, as seen from above. All other components are attached on this sheet. On the system board, you will find the Central Processing Unit (CPU), underlying circuitry, expansion slots, video components, random access memory (RAM) slots, and a variety of other chips.
Types of System Boards
There are two major types of system boards: integrated and nonintegrated:
Nonintegrated system board Each major assembly is installed in the computer as an expansion card. The major assemblies we're talking about are items like the video circuitry, disk controllers, and accessories. Nonintegrated boards can be easily identified because each expansion slot is usually occupied by one of these components.
Integrated system board Most of the components that would otherwise be installed as expansion cards are integrated into the motherboard circuitry. Integrated system boards were designed for simplicity. Of course, there's a drawback to this simplicity: When one component breaks, you can't just replace the component that's broken; the whole motherboard must be replaced. Although these boards are cheaper to produce, they are more expensive to repair.
NOTE
With integrated system boards, there is a way around having to replace the whole motherboard when a single component breaks. On some motherboards, you can disable the malfunctioning onboard component (e.g., the sound circuitry) and simply add an expansion card to replace its functions.
(Continues...)
Excerpted from A+ Complete Study Guideby David Groth Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
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