Page 40 - UNI 101 Computer Science Handout.

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Figure 11 Point-to-Point and Multipoint Buses

The parallel bus does have a number of disadvantages, though. Parallel buses are expensive and
consume a considerable amount of space. Connectors used with parallel buses are also expensive

because of the large number of pins involved. External parallel buses, such as printer cables are also

expensive because of the large number of lines required. More seriously, parallel buses are subject to
radio-generated electrical interference between the different lines at high data transfer rates. The

higher the data rate, the worse the interference, which ultimately limits the speed at which the parallel

bus can operate. Additionally, there is a slight difference in time delay on different lines, known as skew,

as signals traverse the bus. The transfer rate, and thus the clock speed of the bus, is also limited by the
requirement that the data must not change faster than the maximum skew time .Both of these problems

can cause data corruption. Finally, the cost of fiber optic technology makes a parallel optical cable

impractical. Data on a serial bus is transferred sequentially, one bit at a time. Although you might think

that the throughput of a serial bus would be lower than that of a parallel bus theoretically capable of
the same per line transfer rate, the limitations noted above make serial bus transmission attractive in

many circumstances. Indeed, with advances in serial bus technology, serial buses are now preferred for

many, if not most, applications requiring high data transfer rates. Generally, a serial bus has a single data

line pair and perhaps a few control lines. (For simultaneous two-way communication, a second data line

40 Academic Year 2025/2026