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Do you really need a Haswell compatible PSU to use Haswell's C6/C7 states?

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July 2, 2013 12:55:34 AM

Haswell has a new processor state called C6/C7 which reduces the processor's power usage when idle, the new state consumes so little power that they say older or cheaper power supply couldn't be stable with Haswell. But the CPU is on the 12 Volt rail, which is shared by graphics cards, fans, hard drives and so on. So my question is, wouldn't all the things on the 12 Volt rail consume enough power on idle to keep the system stable?
July 2, 2013 12:59:50 AM

You don't have to. Just disable C6/C7 states from BIOS if your PSU doesn't support it. Nothing will go wrong, beside 3-5 watts more when idling.
July 2, 2013 1:10:19 AM

Most good power supplies will support it even if they aren't officially announced to, but like Madness says, it's absolutely pointless for the desktop environment anyways; it's a marketing gimmick there.
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July 2, 2013 2:02:17 AM

Madn3ss795 said:
You don't have to. Just disable C6/C7 states from BIOS if your PSU doesn't support it. Nothing will go wrong, beside 3-5 watts more when idling.


No, you didn't get what I meant. Read my last sentence.

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July 2, 2013 2:12:06 AM
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I think you didn't get it right... The idea of those c6/c7 states is that the PSU must be able to release a low enough amount of Amps for the CPU ( the 12V line for the CPU that is separated from the main 12V rail ). Less amp leads to less watt consumed by the PSU. It's amp, not watt, and has nothing to do with power consumption of other components during idling. A PSU that has its minimum limit of amp on 12V line output higher than what those states require isn't capable of keeping the system stable in those states and might run into trouble ( therefor we have to disable it ).
August 14, 2013 11:52:18 PM

Madn3ss795 said:
I think you didn't get it right... The idea of those c6/c7 states is that the PSU must be able to release a low enough amount of Amps for the CPU ( the 12V line for the CPU that is separated from the main 12V rail ). Less amp leads to less watt consumed by the PSU. It's amp, not watt, and has nothing to do with power consumption of other components during idling. A PSU that has its minimum limit of amp on 12V line output higher than what those states require isn't capable of keeping the system stable in those states and might run into trouble ( therefor we have to disable it ).


Those 12V lines are not independent. The chances are in a cheap or older PSU, which is what we are talking about, those 12V lines are simply connected together in the PSU. A few drives also on the 12V line should be enough to keep the voltage regulated regardless of what the motherboard is doing. There is nothing to suggest that the PSU could not maintain its voltages without any load. The change in CPU specs reflects current capabilities not some futuristic 'make everything redundant' ploy. Relax.
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