Computer Hardware Main Components.pdf

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The Indispensable
PC Hardware Book
Your Hardware Questions Answered
THIRD EDITION
Hans-Peter Messmer
UNIVERSITAT JAUME
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Part 1
Basics
This chapter outlines the basic components of a personal computer and various related peripherals
as an introduction to the PC world. Though this chapter is intended for beginners, advanced users
would also be better prepared for the later and more technically demanding parts of the book.
1 Main Components
1.1 The Computer and Peripherals
Personal computer (PC), by definition, means that users actually work with their own apersonaln
computer. This usually means IBM-compatible computers using the DOS, OS/2 or Windows
(NT) operating system. Mainframe users may wonder what the difference is between a PC and
a
terminal:
after all, a terminal also has a monitor, a keyboard and a small case like the PC, and
looks much the same as that shown in Figure 1.1. Where there is a difference is that the PC
contains a small but complete computer, with a processor (hidden behind the names 8086/SOSS,
80286 or i486, for example) and a floppy disk drive. This computer carries out data processing
on its own: that is, it can process files, do mathematical calculations, and much more besides.
On the other hand, a terminal only establishes a connection to the actual computer (the main-
frame). The terminal can’t carry out data processing on its own, being more a monitor with poor
input and output capabilities that can be located up to a few kilometres away from the actual
computer. That a small PC is less powerful than a mainframe occupying a whole building seems
obvious (although this has changed with the introduction of the Pentium), but that is only true
today. One of the first computers (called
ENIAC,
developed between 1943 and 1946, which
worked with tubes instead of transistors) occupied a large building, and consumed so much
electricity that the whole data processing institute could be heated by the dissipated power!
Nevertheless, ENIAC was far less powerful than today’s PCs.
Because PCs have to serve only one user, while mainframes are usually connected to more
than 100 users (who are
logged in
to the mainframe), the impact of the lack of data processing
performance in the PC is thus reduced, especially when using powerful Intel processors. An-
other feature of PCs (or microcomputers in general) is their excellent graphics capabilities,
which are a necessary prerequisite for user-friendly and graphics-oriented programs like Micro-
soft’s Windows. In this respect, the PC is superior to its <<big brother,,.
Figure 1.1 shows a basic PC workstation. The hub, of course, is the PC, where you find not only
the above-mentioned processor but one or more floppy disk drives, hard drives, interfaces and
other devices. These are dealt with in some detail in Section 1.2. Because you can’t enter
2
Chapter 1
b.
Monitor
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Figure
1.2:
Basic
PC
equipment.
commands into the actual PC, or receive data from it, a
keyboard
(for entering commands and
data) and a
monitor
(fo; data output) are also present. High quality computer monitors are far
more powerful (and therefore much more expensive) than a TV.
With this equipment you can start work: for example, entering text files, doing mathematical
calculations, or playing computer games. To use the PC’s graphics capabilities (with Windows,
for example) a mouse is usually needed. In this book, CCPG~ always means the sum total of these
components, because without a keyboard and a monitor you can’t control the machine.
For printing text files, of course, you need a printer. By using various
interfaces you
can connect
additional
peripherals
like a
plotter
(for drawing plans with coloured pencils) or a
modem
(for world-
wide data communication). ccl’eripherals) means all those units located outside the PC’s case.
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1.2 Inside the Personal Computer
This chapter deals with the various components of a PC, starting with basic definitions of
concepts like the motherboard, the controller etc; their functions are outlined. Also, an overall
picture of the interworkings between individual components is given.
,
1.2.1 How to Open the Case
To work with a PC or to understand how it works, you don’t, of course, need to open the case.
But I think there are a lot of curious users who will soon want to look inside. The following
gives some tips on doing this, while trying to avoid burnt-out electric components and rather
unpleasant electric shocks. To open the case you’ll need a screwdriver and some common sense.
It is best to use a magnetic screwdriver because, in my own experience, one or more screws will
inevitably fall into the case. With a magnetic screwdriver you can get
them
out quite easily.
1
1
1
Main Components
3
You may have heard that magnetic objects should never be placed near a PC. 1 would like to
comment on this:
the Eal;h has a magnetic field;
if you scratch your disk with a sharp object you do so at your own risk; it doesn’t matter
whether it is a knitting needle, a hammer or a magnetic screwdriver;
opening a hard disk drive means losing the data simply because of the dust that is always
present in the air; whether the hard disk is disturbed magnetically afterwards is completely
insignificant;
the distance between the read/write heads and the disk surface is less than about 1 pm.
In
principle, the Earth’s magnetic field is shielded by the PC’s metal case, but as soon as you
remove the cover the magnetic field penetrates all the components. As all electronic and mag-
netic components are exposed to the Earth’s magnetic field when the computer is assembled,
this obviously can’t have an adverse influence. Floppy and hard disks are coated with a thin
magnetizing layer: if someone deliberately scratches off this coating, he really doesn’t know
what he is doing. The data medium of the hard disk drives is enclosed in a case so that dust
particles in the air don’t act as a sort of scouring powder. Therefore, the hard disk is destroyed
not by magnetic but by mechanical action. Whether you are additionally damaging the still
present magnetic pattern with a magnetic object after the mechanical destruction of the data
medium would seem to be unimportant.
Finally, the distance between the read/write heads and the data medium is less than about
1 pm. Because of the protective envelope the closest you can bring the screwdriver to the data
medium of a floppy disk is one millimetre away at most. That is one thousandth of the head-
data medium distance. According to magnetostatic laws, the strength of the magnetic field
decreases in proportion to the square of the distance. This means that the screwdriver must have
a local field strength which is one millionth of the field of the read/write head. Perhaps someone
could show me this monster of a screwdriver with its superconducting magnet! In the case of
hard disk drives, this ratio is much greater because of the additional separation provided by the
drive’s case.
The dangers of mechanical destruction are clearly far more likely. I always use a magnetic
screwdriver because I always lose a screw in the case, and because of the danger of a short
circuit caused either by the screw or by a rash action after having tried to get the screw out.
Advice: If your case is sealed and there is a notice advising
that breaking the seal will invalid-
ate the warranty, you should open the case only after having contacted
your dealer.
Figure 1.2 shows three examples of PC cases (two desktops and one tower), which are the most
common types.
If you are one of those lucky PC buyers who got a technical reference book or at least a user
handbook when you bought your PC, you should have a look at this handbook first to find out
how to open the case. If you’ve found this information, then follow the manual and ignore the
next paragraph.
6
Chapter 1
devices the board is connected to. The individual components are presented below in greater
detail.
1.2.2 Data Flow inside the PC
Personal computers, like other computers, are used for
electronic data processing (EDP).
For this,
data must be input into the PC, and the PC has to supply (the resulting) data. Between input
and output, a varying amount of data processing takes place using a program. Figure 1.5 shows
a typical PC with the most important functional units necessary for data processing.
,---------
/’
. . ..__...._......._..............................~........
Figure 1.5: Block
diagram
of
a
PC with
peripherals. The arrows indicate the direction
of
the
data flow. The
80x86
CPU
and the RAM are located on the
motherboard.
All parts surrounded by the broken line are normally inside the PC me.
The main part is the processor, also called the 80x86 Central Processing Unit
(CPU) (x
is a
dummy variable from e#~ to cc4>> or Pentium to denote the 8086/8088, 80186, 80286, i386, i486,
Pentium family of Intel processors used in IBM-compatible PCs). Because of the large number
of incoming and outgoing arrows, it can be seen that this processor represents (so to speak) the
heart of the computer, in which all data processing events take place. Immediately next to the

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