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?
Do you really need a Haswell compatible PSU to use Haswell's C6/C7 states?
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Madn3ss795
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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.
Madn3ss795
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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 ).
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.
photonboy
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Old link, but let me make this as CLEAR as possible though you can find a detailed explanation if need be online:
*Enabling the low-power state for a Haswell setup (socket 1150 motherboards) will cause the computer to crash coming out of Standby.
The ONLY solutions are:
a) Disable the low-power state (C6/C7; see motherboard though it may not refer to it by name)
b) Avoid Standby (Hibernate or Off)
c) Buy a compatible Power Supply
*I ordered a BE QUIET power supply that claims support for this but testing indicates it doesn't work so I haven't even opened the box yet. I have contacted the company though.
Most power supplies fail this and since I wasn't aware of the issue I suspect the DEFAULT state for C6/C7 is disabled so it consumes slightly more power.
Other:
Intel has a new service called "READY MODE" that's coming soonish which reduces power to roughly 8Watts (a "listening" state) so it can stay on all the time as well as be accessible through the Internet and do automated backups or updates.
I don't know if enabling this feature will force the C6/C7 state or whether you can avoid that with slightly more power. I'm pretty certain it will still work fine you'll just use a few more Watts.
*Enabling the low-power state for a Haswell setup (socket 1150 motherboards) will cause the computer to crash coming out of Standby.
The ONLY solutions are:
a) Disable the low-power state (C6/C7; see motherboard though it may not refer to it by name)
b) Avoid Standby (Hibernate or Off)
c) Buy a compatible Power Supply
*I ordered a BE QUIET power supply that claims support for this but testing indicates it doesn't work so I haven't even opened the box yet. I have contacted the company though.
Most power supplies fail this and since I wasn't aware of the issue I suspect the DEFAULT state for C6/C7 is disabled so it consumes slightly more power.
Other:
Intel has a new service called "READY MODE" that's coming soonish which reduces power to roughly 8Watts (a "listening" state) so it can stay on all the time as well as be accessible through the Internet and do automated backups or updates.
I don't know if enabling this feature will force the C6/C7 state or whether you can avoid that with slightly more power. I'm pretty certain it will still work fine you'll just use a few more Watts.
kaliuseruser
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- Sep 28, 2014
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Im planning to buy a be quiet dark power pro 10 750w psu and I want to make sure it will work with haswell c6/c7 (actually devil canyon but I guess they are they same). can you tell me which be quiet model you tested with haswell and didn't work ?
Sorry guys I haven't been on Tom's for a while but here's what happens after some testing a while back, I put my computer in sleep mode with C7 state enabled using a 4690K and a Seasonic M12II-520 power supply aaaaaannnd it wouldn't turn back on that I had to switch off the power supply and turn it back on to recover. Now with the C7 state disabled I can happily put my computer to sleep, so yeah you do need a Haswell compatible PSU to run C7 state.
SteelCity1981
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- Sep 16, 2010
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to counter this many motherboard vendors have actually disabled the c6/c7 states in the bios by default, so that older and cheaper psu's not capable of running in that low of state won't be affected.
alexandergc
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- Jan 8, 2012
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I've had the exact same experience with my PC.
Z87 motherboard and Haswell CPU, but older PSU.
I tried enabling C6/C7 and it works until you put the PC to sleep.
A power cycle is necessary to wake it up...which is really inconvenient and totally defeats the purpose of Sleep mode, so I turned off C6/C7 and voila~ everything is right with the world again.
Z87 motherboard and Haswell CPU, but older PSU.
I tried enabling C6/C7 and it works until you put the PC to sleep.
A power cycle is necessary to wake it up...which is really inconvenient and totally defeats the purpose of Sleep mode, so I turned off C6/C7 and voila~ everything is right with the world again.
alexandergc
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I'm assuming it will only use the older power states since those have long-standing support.
The difference isn't really all that significant since it's 0.05A vs 0.5A on the 12V rail, which works out to 0.6W versus 6W.
If you're going to leave your computer on standby for a long period of time, you might as well just shut it down or hibernate.
Related article on the link below:
http://www.legitreviews.com/what-enabling-c6c7-low-power-states-do-on-the-core-i7-4770k-haswell-cpu_2217
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