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Something I'm working on wants a very fast/wide Front Side Bus (FSB). What component is the FSB part of? Is it part of the CPU or the motherboard? Is it something that can be placed on a board, or is it fundamentally a part of the motherboard and therefore not able to be replaced?

  • It's baked into the board and can't be replaced or swapped out. – ztk Jul 6 '15 at 17:28
  • You mean baked into the CPU... – Moab Jul 6 '15 at 17:35
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    Both, since the FSB was the link between the CPU and the Northbridge. – David Schwartz Jul 6 '15 at 17:37
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    This confusion is the exact source of my question... – GreySage Jul 6 '15 at 17:47
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The Front Side Bus was once the link between the CPU core(s) and the memory controller back when the memory controller was in the Nortbridge. Modern CPUs and motherboards don't have front side buses because the memory controller is now built into the CPU.

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    Are you saying the FSB is an out-dated concept? What should I be looking for instead on modern systems? – GreySage Jul 6 '15 at 17:52
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    @GreySage Yes. I don't know what you should be looking for instead because I don't know what you're actually looking for. But I would imagine any performance/sizing recommendations based on such ancient technology would be totally irrelevant on modern hardware. The CPU architecture has changed so much I wouldn't assume anything that was the bottleneck way back when would be likely to be the bottleneck today. It could be totally different. – David Schwartz Jul 6 '15 at 18:21
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    Yes, it's outdated. There is no longer anything called an FSB or that has its same role: In the FSB designs, the FSB handled both memory and all of the IO devices' transfers. There is no longer a single connection to the CPU that does all of that. What are you trying to optimize? Bandwdith to memory, bandwidth to I/O devices, number of I/O devices...? A comparison of the diagrams in the WP articles on "Front-side bus" and "Platform Controller Hub" may be helpful. – Jamie Hanrahan Jul 6 '15 at 18:24
  • A bus of some kind between the CPU and the motherboard is required and will likely always be. A few (not many) of the Northbridge functions now exist on the new PCH chip (which is basically the new Southbridge). The PCH is connected to the CPU by both FDI and DMI. I'd say that these two buses would be the closest modern equivalent to a FSB (but the FDI is only used for integrated GPUs). It isn't the same but these buses are transmitting some of the same information as the FSB once did (but it is reusing the DMI link which was once only the link between the North and South to do it). – krowe Jul 7 '15 at 4:08
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    @DavidSchartz I would want to clarify that it is the memory controller hub and not just the memory itself that the FSB is attached to. The FSB carries all peripheral traffic as well. – Shiv Jul 8 '15 at 0:10

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