Wednesday, 16 October 2013

Bus Structures in Computer Organization

If you are interested in learning about computer organization and architecture, the basic thing you need to know is about a 'BUS'.

What is a bus?
When a word of data is transferred between units then all its bits are transferred in parallel i.e; the bits are transferred simultaneously over many wires or lines as one bit per line. A group of such lines that serves as connecting path for several devices is called a 'bus'.
Bus structures are of two types namely - 'Single bus structure' and 'Multiple bus structure'.

Single Bus Structure:
The simplest way to interconnect functional units is to use a single bus as shown below. 


All units are connected to this bus.The main advantage of the single-bus structure is its low cost and its flexibility for attaching peripheral devices. Memory and processor units operate at electronic speeds, making them the fastest parts of a computer. 

Multiple Bus Structure:
It is of two types namely- 'Traditional bus architecture' and 'High performance bus architecture'. 



There is a local bus that connects the processor to a cache memory and a local i/o controller. The cache memory controller connects to the system bus also, which is attached to all the main memory modules.
It is possible to connect i/o controllers directly onto the system bus and the most efficient solution is to make use of one or more expansion buses.
           An expansion bus interface buffers data transfers between the system bus and the i/o controllers on the expansion bus.  Some of the devices attached to the expansion bus are:
  • Network connections which include Local Area Network(LAN) and Wide Area Network(WAN).
  • SCSI(Small Computer System Interface) is itself a type of bus used to support local disk drives and other peripherals.
  • Modem(Modulator and Demodulator) is used to convert analog signals to digital signals and vice versa.
  • A serial port could be used to support a printer or scanner.


The traditional bus architecture is efficient but begins to breakdown as higher and higher performance is seen in the i/o devices. So we go for the 'High Performance Bus Architecture' in which a high-speed bus is used.

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