Haswell CPUs incompatible with Older Power Supplies

A report pointed out that there is a possibility of a compatibility issue with systems using the upcoming 4th generation Intel Core Series Haswell processors with older or cheap power supplies, specifically it may prevents such systems to be powered up by such power supplies from utilizing Haswell’s Shark Bay Platform’s C6/7 power States function.

Haswell will be coming with a lot of integration unlike the previous generations, such as integrated VRMs. It will also be coming with inter-generational IPC improvements, newer x86 instructions and better onboard graphics for gaming and other requirements, even fine tuned power gating  which will allow the processor to go in and out of deeper idle states in an effort to save power.


As shown above, Haswell’s C6/7 power state implementation will require the power supply with the ability to supply a minimum current load of 0.05 amps on CPU’s 12V2 Rail (0.6W). Until the 3rd generation Intel Core Series, it only needed to maintain 0.05 amps.

Meaning that if you plan to use older power supplies which cannot supply a minimum current load of 0.05 amps on the CPU’s rail, this would trigger the Under Voltage Protection/ Over Voltage Protection shutdown whenever the system hits in that deep idle state of 0.05 amps.

As of now, no power supply manufacturers- from a bargain bin to mid series or even high-end Enthusiast level power supplies- don’t mention minimum load readout because until now, the minimum power state consumption wasn’t something one didn’t have to worry about. This would be more concerning for those who plan to make certain upgrades on their existing system and leave the rest to be the same.


But since everyone is practically kept in the dark, till the time power supply manufacturers update their current lineup or roll out their newer power supply to be “Haswell Compatible”, there’s really no choice other than for motherboard manufacturers to implement a bios-level toggle option to enable/disable C6/C7 Power States.

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