SYSTEM BUS

SYSTEM bus is also called as front side bus (FSB),processor bus,Memory bus,System bus.
It connects the CPU with the main memory and is used to connect to other components within the computer. The FSB can range from speeds of 66 MHz, 133 MHz, 100 MHz, 266 MHz, 400 MHz, and up. The FSB is now another important consideration when looking at purchasing a computer Motherboard or a new computer.

The FSB speed can generally be set either using the system BIOS or with jumpers located on the computer motherboard. While most motherboards will allow you to set the FSB to any setting, ensure that the FSB is properly set unless you plan to Overclock the computer.

Issues such as hardware lockups, data corruption or other errors may arise with older hardware, such as old SCSI cards and a newer front side bus such as a motherboard with a 100MHz FSB. Verify your component's compatibility with your motherboard and/or Motherboard FSB speed. In addition, verify that the FSB is properly set; overclocking the computer can also cause these types of issues.

Some computers also have a back side bus which connects the CPU to a memory cache. This bus and the cache memory connected to it are faster than accessing the system RAM via the front side bus.

The bandwidth or maximum theoretical throughput of the front side bus is determined by the product of the width of its data path, its clock frequency (cycles per second) and the number of data transfers it performs per clock cycle. For example, a 32-bit (4-byte) wide FSB operating at a frequency of 100 MHz that performs 4 transfers per cycle has a bandwidth of 1600 megabytes per second (MB/s).

The number of transfers per clock cycle is dependent on the technology used. For example, GTL+ performs 1 transfer/cycle, EV6 2 transfers/cycle, and AGTL+ 4 transfers/cycle. Intel calls the technique of 4 transfers per cycle Quad Pumping.

Notice that many manufacturers today publish the speed of the FSB in megatransfers per second (MT/s), not the FSB clock frequency in megahertz (MHz). This is because the actual speed is determined by how many transfers can be performed each clock cycle as well as by the clock frequency. For example, if a motherboard (or processor) has a FSB clocked at 200 MHz and performs 4 transfers per clock cycle, the FSB is rated at 800 MT/s.