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Figure 1. Von Neumann model of computer architecture

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The Central Processing Unit (CPU) is responsible forinterpreting and executing most of the commandsfrom the computer's hardware and software.

The CPU could be considered the "brains" of thecomputer.

On large machines, the CPU requires one or moreprinted circuit board. On personal computer and smallworkstations, the CPU is housed in a single chip calleda microprocessor

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usually consists of a mixture of :1. RAM (Random Access Memory)2. ROM (Read Only Memory).

Memory has two purposes: store the binary codes for the sequences of

instructions you want the computer to carryout.

store the binary-coded data with which thecomputer is going to be working . This datamight be the inventory records of a

supermarket, for example.

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allows the computer to take in data from theoutside world or send data to the outside world.

Peripherals such as keyboards, video displayterminals, printers, and modems are connectedto the I/O section.

These allow the user and the computer tocommunicate with each other.

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The actual physical devices used to interface the

computer buses to external systems are oftencalled ports.

Ports in a computer function just as shipping ports do for a count.

An input port allows data from a keyboard, an A/Dconverter, or some other source to be read into thecomputer under control of the CPU.

An output port is used to send data from thecomputer to some peripheral, such as a video displayterminal, a printer, or a D/A converter.

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The data bus consists of 8, 16, or 32 parallelsignal lines.

As indicated by the d o u b l e -en d ed ar r o w s onthe data bus line in Figure 1, the data bus linesare bidirectional .

This means that the CPU can read data in frommemory or from a port on these lines , or it cansend data out to memory or to a port on theselines.

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The address bus consists of 16, 20, 24, or 32parallel signal lines.

On these lines the CPU sends out the addressof the memory location that is to be written toor read from.

The number of memory locations that the CPUcan address is determined by the number ofaddress lines.

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The control bus consists of 4 to 10 parallelsignal lines.

The CPU sends out signals on the controlbus to enable the outputs of addressedmemory devices or port devices.

Typical control bus signals are Memory Read,Memory Write, I/O Read, and l/O Write.