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Can someone explain the different system multipliers? I know this is a base clock (a.k.a the System clock) then there is a multiplier for the Front side bus (FSB), RAM module, maybe for the RAM chips, and other internal busses like PCI, AGP, etc. Also, are some multipliers based on other multipliers?

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2 Answers 2

Essentially everything internal has a multiplier due to it's need to run synchronously, whereas most (all?) external devices run asynchronously. Some of these internal devices are only at a multiplier of 1.

What a multiplier does is it takes a base cycle time and shortens it (since frequency is inverse to the cycle time it thus multiplies it's frequency). Because of their synchronisity operations will happen on either a rising or falling or both clock edges and shortening the cycle time will then increasing their data throughput. The most important of these is the FSB which interconnects the CPU to Memory. This is a major choke point in system performance due to the slowness of memory compared to CPU cycle time.

Off topic a bit SRAM runs at about .5-5 nanoseconds, DRAM 50-70 nanoseconds, magnetic disks 2-5MS. Also the width of the bus from the CPU to Memory also effects performance greatly, but this is not configurable by an end user.

The south bridge and south side bus interfaces with PCI and AGP mezzanine buses and to my knowledge these cannot have their clock rates altered by an end user.

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You can read all about this at wikipedia

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