8 Computer Service and Repair
Hexadecimal Decimal
0 0
1 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8
9 9
A 10
B 11
C 12
D 13
E 14
F 15
Goodheart-Willcox Publisher
Figure 1-8. Hexadecimal numbers include the digits
0
through
9
and the letters
A
through
F.
Binary numbers are too long and awkward to be
used to express computer values such as memory
locations. Thus, hexadecimal numbers are used
instead. The hexadecimal code uses less space.
The hexadecimal system best matches the
hardware system of most computers. As you
will learn, data lines in a computer are eight,
sixteen, thirty-two, or sixty-four lines wide. They
use increments of eight and sixteen, which work
beautifully with a hexadecimal system.
In addition, the number values you will
encounter that are used to express memory sizes
(such as 256, 512, and 1024) are increments of 16.
As you can see, a number system based on 16 is
used to best match the digital electronic system of
computers.
Both the binary and hexadecimal number
systems will be used to express values and
illustrate computer operation many times
throughout the study of computer systems.
ASCII Code
ASCII (pronounced as-key) stands for
American Standard Code for Information
Interchange. It was the first attempt to
standardize computer character codes among the
varieties of hardware and software. When a key
on a computer keyboard is pressed, for example,
the letter M, all computer systems display the
letter M on the monitor screen. When the letter
M is sent to the printer, the letter M is printed as
expected. Figure 1-9 is a listing of character codes
and their ASCII code representatives.
The ASCII system was a great attempt to
standardize the computer coding system, but
it had limitations. The extended character set
is unique to certain systems, such as IBM or
equivalent machines. The extended character
set must be used with a compatible software
system; otherwise, unexpected characters will be
generated. In addition, the standard form of ASCII
does not allow for common requirements of word-
processing packages such as bold, italic, underline,
or variations in fonts. ASCII was meant for symbol
compatibility used for basic data files. ASCII is
still used today, especially when data needs to
be transferred between two different software
programs.
Bits, Bytes, and Words
Bit, byte, and word are basic computer units of
data based on the binary number system. Short for
binary digit, a bit is a single binary unit of one or
zero. A byte is equal to eight bits. Early computers
processed data in patterns of these eight-bit bytes.
A word is the total amount of bytes a
computer can process at one time. Consequently,
the length of a word can vary from computer to
computer. For example, many computer systems
process either 32 or 64 bits at one time. Hence,
a word in those machines would consist of
32 bits (4 bytes) or 64 bits (8 bytes), respectively.
Computers are often compared by the size of the
word they can process.
Bit = 0 or 1 1
Byte = eight bits 01011110
Word = 1 to 8 bytes 10010010
11110000 00110011 10101010