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System bus has control, address and data buses, as we can see in this picture

http://en.wikipedia.org/wiki/File:Motherboard_diagram.svg

I think the front-side bus and memory bus is directly on the system bus, but what about the PCIExpress and PCI buses, are they directly connected to the system bus? Or do they just all connect to a hub or controller, and the hub or controller is connected to the system bus?

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There really isn't a "system bus" any more. This is like asking where the horeshoes are on a car.

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The short answer is no.

To steal from @Sickest and the link in his comment and elaborate:

That image you provided is outdated. Modern architecture actually moved the memory controller from the North Bridge to directly on the CPU.

enter image description here

And if you ever look at your motherboard, you will see many controllers and chips that peripherals must communicate with before they hit the more core System Bus:

enter image description here

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    On modern x86 CPUs, the high-speed PCIe controller is on the CPU die and there really is no "Frontside Bus" other than between the cores. The closest thing is the DMI bus, which is more like PCIe than a traditional system bus. – David Schwartz Feb 13 '14 at 12:17
  • @DavidSchwartz Thanks! I thought about going further, but it could become a full book rather quickly, so I just stopped when I thought the point was illustrated well enough. As far as modern goes... When is the last time anyone used ISA anyway? – Austin T French Feb 13 '14 at 12:20

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