Monday, August 2, 2010


Hello everyone
I wanted to know what is FSB? what are its physical significance & where is it located??
it would be quite helpful for me to undertsand FSB if any of u posts the answer of my doubts


  1. In PC's,the front-side bus (FSB) is the bus that carries data between the CPU and the memory controller hub.

    Depending on the processor used,some computers may also have a back-side bus that connects the CPU to the cache.This bus and the cache connected to it are faster than accessing the system memory(or 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(in bytes),its clock frequency (cycles per second) and the number of data transfers it performs per clock cycle.
    example,a 64-bit(8-byte)wide FSB operating at a frequency of 100 MHz that performs 4 transfers per cycle has a bandwidth of 3200MB/s

  2. Just an additional note, the memory controllers on AMD platforms have been on the CPU itself for a long time, and the same has come to Intel with the new Core i series processors. They've moved the memory controller from the chipset to the CPU die itself, which means the concept of FSB as we know it is now kinda, hmm, irrelevant. The integrated memory controllers have direct access to memory. Although FSB speeds still are technically there, they are much higher and the bandwidth doesn't just depend on the FSB frequency anymore.

    I thought I could have posted a new blog but then thought its related to this so I'd just put it as a comment!

  3. Thanks shruti it really helped me to know what he FSB is. Thanks for being straight & short in ur explanation.

  4. are welcome:)
    @kshitiz could you please give us the full form of 'AMD' platforms and explain the other factors on which the FSB bandwidth depends..
    thanx in advance

  5. This comment has been removed by the author.

  6. AMD(Advanced Micro Devices) is a microprocessor company, just like Intel. They make processors, and their "platforms" which actually means the chipset designed to run with the processor.

    The FSB bandwidth depends on its clock speed, its width(like say, in bits) and the amount of data transfers it performs per cycle. So say, an FSB with 200Mhz clock frequency, 64-bits wide and doing 4 data transfers would give you 64 x 200 x 4 Megabits per second, or around 6400MB/s(Megabytes per second) of available bandwidth. :) This bus is mainly to connect the CPU and the chipset(which is connected to the memory), and the more bandwidth it has, the faster is the access to the RAM, for the CPU.

    In traditional designs, the memory controller (which acted as the mediator between the memory and the CPU) resided on the motherboard's chipset. The FSB linked the chipset and the CPU, which is why they always needed a faster link to the Chipset in order to allow faster access to the Memory. In modern designs (not so modern for AMD processors, for Intel it began with the new core i3/i5/i7 series) the memory controller has been integrated into the CPU itself, which means the need for a mediator is now finished, the CPU has direct access to the memory. The "FSB" still links the chipset to the CPU, but now the need for a ridiculously fast bus is not there, its only there to connect other peripherals indirectly to the CPU.

    Hope this made it clear, if not let me know and I can try again! :)