What is BUS...?

Bus

*)     Bus is nothing but the cables, printed circuits, etc.


*)     A bus, in computing, is a set of physical connections which can be shared by multiple hardware components in order to communicate with one another. 


*)   The purpose of buses is to reduce the number of "pathways" needed for communication between the components, by carrying out all communications over a single data channel. This is why the metaphor of a "data highway" is sometimes used.

Characteristics of a bus

A bus is characterised by the amount of information that can be transmitted at once.

This amount, expressed in bits, corresponds to the number of physical lines over which data is sent simultaneously.

A 32-wire ribbon cable can transmit 32 bits in parallel.

The term "width" is used to refer to the number of bits that a bus can transmit at once. 

The bus speed is also defined by its frequency (expressed in Hertz), the number of data packets sent or received per second.

Each time that data is sent or received is called a cycle. 

This way, it is possible to find the maximum transfer speed of the bus, the amount of data which it can transport per unit of time, by multiplying its width by its frequency.

A bus with a width of 16 bits and a frequency of 133 MHz, therefore, has a transfer speed equal to: 

 

16 * 133.106 = 2128*106 bit/s,
or 2128*106/8 = 266*106 bytes/s
or 266*106 /1000 = 266*103 KB/s
or 259.7*103 /1000 = 266 MB/s

Bus sub assembly

• The address bus (sometimes called the memory bus) transports memory addresses which the processor wants to access in order to read or write data. It is a unidirectional bus.
• The data bus transfers instructions coming from or going to the processor. It is a bidirectional bus.
• The control bus (or command bus) transports orders and synchonisation signals coming from the control unit and travelling to all other hardware components. It is a bidirectional bus, as it also transmits response signals from the hardware.