Basic Computer Architecture.

System Buses.

The groups of conductors that connect the components in a computer system are called buses. Even a single conductor or wire is referred to as a bus. The diagram below shows the voltage levels on an 8 bit bus corresponding to 10110110 binary.

8 bit bus

There are three important buses in a computer system.

The address bus.

This connects the address register to the memory decoding circuits for each memory location in the system.

The data bus.

This is used to send and return data to and from the microprocessor for processing.

The control bus.

This is typically a single conductor that can either be logic 1 or 0. This determines the direction that the data is sent. To control the direction of the data transfer, the microprocessor transmits a signal on the control bus. This tells the device whether the microprocessor is sending data (write signal), or requires data to be sent to it (read signal).

The core components of a basic computer system are shown below.

basic programmable system


The Central Processing Unit (CPU) is another name for the microprocessor.

Read Only Memory (ROM).

The Read Only Memory is a permanent memory storage device. This type of storage device is called non-volatile, because the information is not lost when the electrical power supply is removed. Binary information is stored by means of open and closed links in the circuit inside the device.

Random Access Memory (RAM).

The Random Access Memory is a non- permanent or volatile memory device. The binary information is stored by latching circuits similar to the one previously described. Transistors require electricity to maintain their status and therefore all the information is lost if the power is removed from the system. When the power supply is reconnected, the transistors flip to a random state, until they are set to a specific condition by the microprocessor.

I/O Controller.

The Input/ Output controller allows other devices such as keyboards mice, monitors and disk drives etc. to be connected to the system.