Microsoft Office Tutorials and References
In Depth Information
Data Representation
printer; a specifi cation for that printer might be a print speed of eight pages per minute or
color output.
The advertisement shown in the Visual Overview includes several specifi cations
describing the computer system shown.
Data Representation
To understand computers, you need to know a little about how data is represented to a
computer. Data refers to the words, numbers, fi gures, sounds, and graphics that describe people,
events, things, and ideas. To a computer, the characters used in human language, such as
the characters in a word processed document, are meaningless because it is an electronic
device. Like a light bulb, the computer must interpret every signal as either “on” or “off.” To
do this, a computer represents data as distinct or separate numbers. Specifi cally, it represents
“on” with a 1 and “off” with a 0. These numbers are referred to as binary digits , or bits .
A series of eight bits is called a byte . As Figure 4 shows, the byte that represents the
integer value 0 is 00000000, with all eight bits “off,” or set to 0. The byte that
represents the integer value 1 is 00000001, and the byte that represents 255 is 11111111.
A kilobyte KB or simply K) is 1024 bytes, or approximately one thousand bytes; a
megabyte MB) is 1,048,576 bytes, or about one million bytes; a gigabyte GB) is
1,073,741,824 bytes, or about one billion bytes; and a terabyte TB) is 1024 GB, or
approximately one trillion bytes. The symbols KB, MB, GB, and TB refer to processing
capacity, storage capacity, and fi le sizes.
Figure 4
Binary representation of numbers
Number
Binary Representation
0
00000000
1
00000001
2
00000010
3
00000011
4
00000100
5
00000101
6
00000110
7
00000111
8
00001000
253
11111101
254
11111110
255
11111111
Personal computers commonly use the ASCII code to represent character data.
ASCII (pronounced “ASK-ee”) stands for American Standard Code for Information
Interchange . The ASCII system translates the decimal numbers 0–255 into binary data.
Each ASCII code represents a letter or character on the keyboard; for example, the ASCII
code 65 represents the character A, and the ASCII code 97 represents the character  a.
Computers translate ASCII into binary data so that they can process it.
The original ASCII system used seven bits to represent the numbers 0 (0000000)
through 127 (1111111) to stand for 128 common characters and nonprinting control
characters. Because bits are usually arranged in bytes, the eighth bit is reserved for error
checking. Extended ASCII uses eight bits and includes the numbers 128 (10000000)
through 255 (11111111) to represent additional characters and symbols. Extended ASCII
 
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