Page 34 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Unit 2: Data Processing

The table shows the number of registers of several mainstream architectures. Note that the stack Notes
pointer (ESP) is counted as an integer register on x86-compatible processors, even though there
are a limited number of instructions that may be used to operate on its contents. Similar caveats
apply to most architectures.

2.4.2 Register Usage

The number of registers available on a processor and the operations that can be performed
using those registers has a significant impact on the efficiency of code generated by optimizing
compilers. The Strahler number defines the minimum number of registers required to evaluate
an expression tree.

2.5 Computer Bus

Computer Bus is an electrical pathway through which the processor communicates with the
internal and external devices attached to the computer. Bus transfers the data between the
computer subsystems and between the computers and sends the instructions and commands to
and from the processor the different devices. It connects all internal computer components to the
main memory and the central processing unit (CPU).

It can logically connect many peripheral devices that can easily communicate with the CPU. A
bus is also known as the data bus, address bus or the local bus. The size of the computer bus is
important because it determines that how much data can be transferred at a time. Additionally it
has the clock speed, which is measured in the MHz. There are different types of the buses which
are discussed below. The name of the bus is determined by the type of the signals it carry and
the operations it performs.

2.5.1 Data Bus

It carries the data between the different components of the computer.

2.5.2 Address Bus
It selects the route that has to be followed by the data bus to transfer the data.

2.5.3 Control Bus
It decides that whether the data should be written or read from the data bus.

2.5.4 Expansion Bus

It is used to connect the computer’s peripheral devices such as printer, modem and scanner with
the processor.
Similarly several different types of the buses are being used on the Apple Macintosh computer.
In the newer Apple Macintosh systems, the Nubus has been replaced by the PCI.
Buses can be parallel and serial. Today, most of the computers have internal and external buses
to connect the internal and external devices to the main memory and CPU. Depending on the
type of the bus and computer the bus’s operation can be unidirectional or bidirectional.

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