Haswell is coming in just over a month, and when it does, it is going to introduce some new power states. These new power states – C6 and C7 – will allow the CPU to consume hardly any power at all while idle. In fact, the power draw is so low, many power supplies will not even support it!
According to VRZone, and confirmed by Tech Report, the new power states require a PSU to be able to deliver 0.05 amps to the 12V2 rail. The problem is that most PSUs can not deliver less than 0.5 amps. Asking them to deliver any less results in stability issues or complete shut down.
The fact that not many power supplies may support this function – and even fewer even give any information about minimum power draw at all – means that it will be very likely that the C6/C7 states can be disabled in the BIOS. If you do have a compatible PSU, you will want to enable this. In most cases, it may be a matter of trial and error. And if it is enabled by default, I can see a lot of people running into stability issues with their shiny new Haswell systems, without knowing the cause.
We should have more information in our full review of the product.