A compatibility issue may prevent systems with older or bargain basement power supply units from utilizing the improved C6/7 low power states that come with the Haswell Shark Bay platform.
Intel's 4th Generation Core Processors (codenamed Haswell, follow-up to last year's Ivy Bridge), is slated to be released later this year in early June, bringing with it the usual inter-generational IPC (instructions per clock) improvements, new x86 instructions like AVX2 for increased parallelism, a more potent iGPU for gaming/compute and fine grained power optimizations/gating that allow the chip to transition in and out of deeper idle states to save power.
According to our sources, the new C6/C7 power states on the Haswell-Shark Bay platform will require the system power supply to be able to maintain a minimum current load of 0.05Amps on the CPU exclusive 12V2 rail (0.6W).
Older or bargain basement power supply units may be unable to achieve this, and might become unstable or trigger a UVP/OVP shutdown once the system enters the C6/C7 power states. This is because the previous ATX12V v2.3 design guidelines for Ivy Bridge and its predecessors only called for a minimum load of 0.5 Amps on the CPU power rail, hence a less sophisticated internal feedback loop/protection could be used in older or cost-reduced offerings, which will not support the new standards.
Most worryingly, PSU manufacturers (even the enthusiast grade ones) do not usually report the minimum load on their spec sheets, so it is virtually impossible for us to come up with a list of supported units at this time. To ensure a smooth transition, mainboard designers and system integrators have been told to implement a BIOS-level toggle to enable/disable the new C6/C7 power states.
Update: 30/4 – Cyril from The Tech Report has also independently confirmed our story and went on to get a statement about it from Corsair's Robert Pierce that the company will be working to check their power supplies for the minimum load compliance.