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gameson

What is Spread Spectrum Clocking?

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I notice that spread spectrum clocking is available on Hitachi T7K500, but I dunno what it is.

Can someone explain and tell me whether it's wise to turn it on?

Please let me know.

Thanks.

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Spread-spectrum (as it applies to motherboard/disk firmware options) modifies IO/processor clock signaling to improve electromagnetic compatibility (EMC) with other devices. Note that it does not improve the device's own immunity to EMF/RFI. Unless you have a device that you suspect may be being affected by EMF/RFI, I recommend leaving spread-spectrum disabled; spread-spectrum often has negative performance/reliability implications for the device on which it has been enabled.

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Yep, spread spectrum clocking will reduce the amount of interference at any one frequency given off by that component / bus / whatever by modulating the signaling frequency a little. The cost is slightly reduced stability for that particular component. There's obviously some stability headroom built into these things, so you have some to spare if there is a need to enable spread spectrum clocking (namely, if you are experiencing any EMI problems in other parts of the system or other devices--in real-world terms, though, I'm not sure how that manifests itself). However, if you are, say, successfully and stably overclocking the AGP bus, then enabling SSC on the AGP bus may render it unstable if you were on the edge to begin with.

With your T7K500, maybe SSC would be bad if your signal integrity was already iffy--like if you were using a really long (or shoddy) cable, or if there was a lot of EMI coming from other components inside your case. I believe I've read that you should leave it off unless there is a need to turn it on.

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SS is typicaly only used when the board maker is trying to pass some Euro emi test, and pretty much for no other reason. I have never seen any reason for an end user to have any form of SS running.

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