10 Computer Service and Repair
Serial and Parallel Data
Transfer
Data is transferred in one of two modes in
a computer system: series or parallel. Ports on
a computer are similarly classified as serial or
parallel. In a serial transfer, data is sent through a
port one bit at a time in successive order. Modems
are used to communicate with other computers
over telephone lines. Because of the limited
capacity in a telephone line, data is transferred
through modems in a serial fashion. Other
examples of serial data transfer are the keyboard
and mouse.
In parallel transfer, more than one bit is sent
side by side. In parallel port transfer, data is sent
eight bits at a time. In general, data is transferred
at a much higher rate through a parallel port than
a serial port. Data is transferred in parallel on the
computer bus system between devices such as the
hard drive, RAM, and the CPU. Figure 1-10 shows a
comparison between serial and parallel data transfer.
Be able to differentiate between serial and
parallel data transmission.
A+ Note
Computer Numerical Values
Metric prefixes are commonly used to
express the speed and size of computer systems
and hardware. Prefixes are usually used in
combination with the word bit (b) or byte (B). For
example, speed is usually expressed in bits. Storage
space is usually expressed as bytes. See Figure 1-11
for a listing of commonly used metric prefixes.
There is some confusion when using metric
prefixes for expressing computer sizes. This is
because there are two possible values for a large
expression such as a megabyte. The nominal
value for megabyte using the base 10 number
The cat ran into ...............
0 1 0 1 0 1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 1 1 1 1
T h e
0
1
0
1
0
1
0
0
T
0
1
1
0
1
0
0
0
h
0
1
1
0
0
1
0
1
e
0
0
1
0
0
0
0
0
0
1
1
0
0
0
1
1
c
0
1
1
0
0
0
0
1
a
Serial data transfers one bit each
digital pulse. There is only one path
for the data to travel through.
Parallel data
can be
transmitted
at 8, 16, 32, or
64 bits per
digital pulse.
T = 01010100 h = 01101000 e = 01100101
Goodheart-Willcox Publisher
Figure 1-10. Serial and parallel data transfer. Serial transfers one bit at a time. Parallel transfers multiple bits, usually
multiples of 8 (1 byte), at a time.