Haswell Could Have Compatibility Problems With Older PSUs
Older or cheaper power supplies might have compatibility with the upcoming Haswell CPUs because they are too efficient.
Yesterday, we gave you a full roundup of all the rumors that we have reported regarding Intel's desktop lineup of Haswell CPUs. In the meantime, yet another rumor has surfaced. According to VR-Zone, a number of power supplies will actually not be able to support the Haswell CPUs, not because they cannot deliver enough power, they cannot deliver a low enough level of power.
While the Ivy Bridge CPUs had a minimum power consumption of 0.5 A in a C6 or C7 state, the next generation of processors would require only as little as 0.05 A, a 10x reduction. The problem is that a number of older or lower-quality power supplies are unable to deliver such low loads at stable voltages, meaning that the system could crash due to unstable voltages when in C6 or C7 state.
Fortunately, there is a solution. Users with problems could simply go into the motherboards' BIOS interface and disable the C6 and C7 power states. However, this would lead to higher power consumption. Fortunately though, most modern power supplies shouldn't have issues with the low power draw. A number of manufacturers are already advertising power supplies that have perfectly stable voltages even down to 0 W, among which is Enermax.
PSU oems will just start making cheap units that support the new CPUs. There will be enough demand to justify it.
The question is how much?
Where Haswell may be more of a challenge to cheap PSUs is response time to large load swings when the CPU keeps bouncing between C7 and full-power: too little feedback bandwidth means the voltage rails will sag when the CPU wakes up which may trip under-voltage lock-outs or surge when the CPU goes to sleep and trip over-voltage lock-outs. Depending on how fast Haswell can switch from full-power to sleep, the PSU's feedback delay could potentially encounter situations where the CPU is already going back to sleep while the PSU is still ramping up from the previous wake-up or vice-versa.
Why so interesting? 0W means 0A at whatever voltages. It's like removing the Processor from the socket and measure the voltage being delivered at the socket pins.
Nothing special/interesting about it: a Lithium battery delivers ~3.6V/cell open-circuit voltage, a fresh alkaline battery delivers ~1.65V/cell, a lead-acid cell delivers ~2.35V, etc. Mains voltage is 115-120V regardless of whether or not you have anything other than your multimeter plugged in. Your PSU's 12V rails are expected to hold 12V regardless of whether or not you have anything plugged in, same for 3.3V and 5V outputs.
Voltages can exist without a load. Voltages and electrical fields are everywhere; even in the vacuum of space.
Electrical current (measured in Amperes) on the other hand does require some form of conductor and load to exist.