Page 39 - UNI 101 Computer Science Handout.

Faculty of Nursing
Adult care Nursing Department

they may be conductors on a printed circuit. Optical conductors work similarly, using light that is directed

from point to point in special thin clear glass fibers.

Optical conductors can carry data much faster than electrical conductors. But their cost is high, which

has limited their use to date. None the less, there is considerable lab research into ways to integrate

more optical circuits into computers. Buses are used most commonly for transferring data between

computer peripherals and the CPU, for transferring data between the CPU and memory, and for

transferring data between different points within the CPU. A bus might be a tiny fraction of an inch long,
carrying data between various parts of the CPU within an integrated circuit chip; it might be a few inches

long, carrying data between the CPU chip and memory; it might even be hundreds of feet long, carrying

data between different computers connected together in a network.

In most cases, a multipoint bus requires addressing signals on the bus to identify the desired destination
that is being addressed by the source at a particular time. Addressing is not required with a point-to-

point bus, since the destination is already known, but an address maybe required if the message is being

passed through the destination point to another location. Addressing is also not required for a multipoint
bus where the signal is actually intended to reach all the other locations at once; this is sometimes the

case for buses that are internal to the CPU. Addressing may be integral to the lines of the bus itself, or

may be part of the protocol that defines the meaning of the data signals being transported by the bus.

Typical point-to-point and multipoint bus configurations are illustrated in Figure below. A parallel bus

that carries, say, 64 bits of data and 32 bits of address on separate data and address lines would require
a bus width of 96 lines, even before control lines are considered. The parallel bus is characterized by

high throughput capability because all the bits of a data word are transferred at once. Virtually every

bus internal to the CPU is a parallel bus, since the high speed is essential to CPU operation. Also most
internal operations and registers are inherently parallel, and the use of serial buses would require

additional circuitry to convert the parallel data to serial and back again. Until recently, the buses that

connected the CPU with memory and various high speed I/O modules such as disk and display controllers

were also parallel, for similar reasons.

39 Academic Year 2025/2026