Table Of ContentA+ All-In-One Certification Exam Guide, 3rd Edition
by Michael Meyers
$59.99; ISBN: 0072126795
A+ All-In-One Certification Exam Guide, 3rd Edition
by Michael Meyers
$59.99; ISBN: 0072126795
Chaper 1
The Visible PC
In this chapter, you will:
• See the major components of a PC.
• Understand the different connectors in a PC.
• Recognize the most common devices inside a PC.
• Learn how to set jumpers and switches.
Mastering the craft of the PC Technician requires you to learn a lot of details about a zillion
things. Even the most basic PC contains hundreds of discrete hardware components, each with
its own set of characteristics, shapes, sizes, colors, connections, etc. By the end of this book, you
will be able to discuss all of these components in detail.
In order to understand the details, you often need to understand the big picture first. "The Visible
PC" should enable you to recognize the main components of the CPU and to understand their
function. You will also see all the major connectors, plugs, and sockets, and learn to recognize a
particular part simply by seeing what type of connector attaches to that part. Even if you are an
expert, do not skip this chapter! It introduces a large number of terms that will be used throughout
the rest of the book. Many of these terms you will know, but some you will not, so take some time
and read it.
It is handy, although certainly not required, to have a PC that you can take the lid off and inspect
as you progress. So get thee to a screwdriver, grab your PC, take off the lid, and see if you can
recognize the various components as you read about them.
Warning! If you decide to open a PC while reading this chapter, you must take
proper steps to avoid the greatest killer of PCs - Electrostatic Discharge (ESD).
ESD simply means the passage of a static electrical charge into your PC. Have
you ever rubbed a balloon against your shirt, making it stick to you? That's a
classic example of static electricity. When that charge dissipates, we barely
notice it happening or don't notice it at all, although on a cool, dry day, I've been
shocked by a doorknob so hard that I could see a big blue spark! If you decide to
open a PC as you read this chapter, jump ahead to the Power Supplies chapter
and read up on ESD and how to prevent it - the life you save may be your PC's!
CPU
The Central Processing Unit (CPU), also called the microprocessor, performs all of the
calculations that take place inside a PC. CPUs come in a variety of shapes and sizes, as shown
in Figure 1-1.
Figure 1: Typical CPUs
Modern CPUs generate a lot of heat and thus require a cooling fan or heatsink in order to run
cool. (Figure 1-2) You can usually remove this cooling device, although some CPU manufacturers
sell the CPU with a fan permanently attached.
Figure 2: Installed CPU under a fan
CPUs have a make and model, just like an automobile. When talking about a particular car, for
example most people speak in terms of a "Ford Taurus" or a "Toyota Camry." When they talk
about CPUs, people say, "Intel Pentium III" or "AMD Athlon." Over the years, there have been
only a few major CPU manufacturers, just as few companies manufacture automobiles. The two
most common makes of CPUs used in PCs are AMD and Intel, although other makers with
names such as Cyrix and IDT have come and gone.
While there have been only a few manufacturers of CPUs, those manufacturers have made
hundreds of models of CPUs. Some of the more common models made over the years have
names (or had - most of these names are obsolete) such as 8088, 286, 386, 486, Pentium,
Pentium Pro, K5, K6, 6x86, Pentium II, Celeron, Athlon, and Pentium III. In the early years of
CPUs, competing CPU manufacturers would sometime make the exact same model, so you
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could get an AMD 486 or an Intel 486 (Figure 1-3 ). This is no longer true, although some models
function similarly, such as the Intel Pentium and the AMD K6.
Figure 3: One AMD 486, one Intel 486
CPUs measure potential performance with a "clock speed," much like an automobile has a
(theoretical) top speed listed on the speedometer. Manufacturers determine the clock speed -
measured in "Megahertz" (MHz) - at the factory. The first CPU used in PCs had a clock speed in
the range of 4.77 MHz. Today's CPUs have clock speeds around 1000 MHz. 1000MHz is equal
to 1 gigahertz (GHz), so we often see the latest CPUs mentioned in terms of GHz. When talking
about a CPU, people often cite the make, model, and clock speed; as in an "833-MHz Intel
Premium III" or a "1.2-GHz AMD Athlon."
Manufacturers produce CPUs of the same make and model with many different clock speeds.
(Figure 1-4) One particular make and model of CPU may come in five or six different speeds! The
main reasons for picking one speed over another are the needs of your system - or the thickness
of your wallet!
Figure 4: Same CPUs, different speeds
Finally, CPUs come in different packages. The most common packages are called PGA (Pin Grid
Array) and SEC (Single Edge Cartridge). You cannot recognize a CPU solely by its package.
Look at Figure 1-5. This figure shows two examples of the popular Celeron processor. Even
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though these two CPUs are virtually identical in terms of speed and power, they look quite
different from each other.
Figure 5: Intel Celeron CPUs
RAM
Random-Access Memory (RAM) stores programs and data currently being used by the CPU.
RAM is measured in units called bytes. Modern PCs have many millions of bytes of RAM, so
RAM is measured in units called megabytes. An average PC will usually have anywhere from 32
megabytes to 128 megabytes of RAM, although you may see PCs with far more or less RAM.
RAM has been packaged in many different ways over the years. The most current package is
called a 168-pin DIMM (dual inline memory module). An older type of RAM package - basically
obsolete but added here for completeness - is called SIMM (single inline memory module). See
Figure 1-6.
Figure 6: SIMM and DIMM RAM packages
SIMMs and DIMMs come in several different physical packages. The two most common sizes of
SIMMs are 30-pin and 72-pin, so named for the number of metal "contacts" along one edge.
(Figure 1-7) It is easy to tell the difference between them, as the 72-pin SIMM is much larger than
the 30-pin SIMM. 72-pin SIMMs are more modern and can hold more RAM than 30-pin SIMMs.
72-pin SIMMs can also transfer information to and from the CPU faster than 30-pin SIMMs can.
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Figure 7: 30- and 72-pin SIMM
There are also three different sizes of DIMMs used by PCs: a 168-pin DIMM and two sizes of
smaller "SO" DIMMs: a 72-pin and a 144-pin version (Figure 1-8). The SO DIMMs' small size
makes them very popular in laptops. Most desktop PCs sold today use only the 168-pin DIMMs,
although millions of older PCs sport SIMMs.
Figure 8: 168-pin DIM and SO-DIMM
Motherboard
You can compare a motherboard to the chassis of an automobile. In a car, everything connects to
the chassis either directly or indirectly. In a PC, everything connects to the motherboard, either
directly or indirectly. A motherboard is a thin, flat piece of circuit board, usually of green or gold
color, and often slightly larger than a typical piece of notebook paper (Figure 1-9).
Figure 9: Photo of bare motherboard
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A motherboard contains a number of special sockets that accept various PC components.
Motherboards provide sockets for the microprocessor (Figure 1-10); sockets for RAM (Figure 1-
11); sockets to provide power (Figure 1-12); connectors for floppy drives and hard drives (Figure
1-13); and connectors for external devices, such as mice, printers, joysticks, and keyboards
(Figure 1-14).
Figure 10: Socket for CPU
Figure 11: Sockets for RAM
Figure 12: Sockets for power plug
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Figure 13: Floppy and hard drive connectors
Figure 14: Various external connectors
Every motherboard has a few components soldered directly onto the motherboard (Figure 1-15).
Figure 15: Soldered components
Motherboards use tiny wires, called "traces," to link the various components of the PC together
electrically (Figure 1-16).
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Figure 16: Traces
All motherboards use multi-purpose "expansion slots" that enable you to add optional
components. Your PC accepts thousands of different types of optional devices, including
scanners, modems, network cards, sound cards, and tape backups. The expansion slots create
the connection that enables optional devices to communicate with the PC. We generically call a
device that connects to an expansion slot an "expansion card," or simply a "card." There are
different types of expansion slots for different types of cards (Figure 1-17).
Figure 17: Expansion slots - one slot has a card inserted
The PC industry long ago standardized the position of the expansion slots and external
components. The motherboard mounts inside the "box" or "case," which is the part of the PC that
you actually see (Figure 1-18).
Figure 18: Motherboard in box
The case needs to have holes that enable devices to access the external connectors. Where the
motherboard has a connector for a keyboard, for example, the case must have a hole though
which you insert the keyboard plug. See Figure 1-19.
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Figure 19: Keyboard socket visible through hole in box
Equally important, if the expansion slots enable you to add cards to the PC, then the case must
also provide slots that enable different devices to connect to their cards (Figure 1-20).
Figure 20: Inserted card from back of PC
Certain types or "layouts" of motherboards require a case designed for that type. Fortunately,
motherboards come in only a few different layouts, which requires only a few different types of
cases. We will visit this in more detail in the Motherboard chapter.
Power Supply
The "power supply," as its name implies, provides the necessary electrical power to make the PC
operate. The power supply takes standard (in the U.S.) 110-volt AC power and converts it into 12-
volt, 5-volt, and 3.3-volt DC power. The vast majority of power supplies are about the size of a
shoebox cut in half, and are usually gray or metallic colored (see Figure 1-21).
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Figure 21: Typical power supply
A number of connectors lead out of the power supply. Every power supply provides special
connectors for the motherboard (Figure 1-22), and a number of other "general-use" connectors
that provide power to any device that needs electricity (Figure 1-23).
Figure 22: Power connectors for motherboard
Figure 23: General use power connectors
You can see the power supply if you look at the back of your PC. It has a connection for a power
plug that in turn runs to an electrical outlet and also has a big fan inside. Every PC uses a fan or
two to keep the interior of the PC cool (Figure 1-24). Check out both the Power Supply and
Motherboard chapters for information detailing power supplies.
Figure 24: Power supply fan
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