Intel Core i7-4770K Haswell Processor

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IGP Energy Efficiency

Much fuss has been made about energy efficiency being key to Haswell's success and we're pleased to report that its light load power consumption is noticeably better than Ivy Bridge. Our i7-4770K system idled at only 21W DC and only an additional 3~4W was required for video playback. This puts it well ahead of the i7-3770K and AMD's A8/A10 APU series. It's not a huge savings in the grand scheme of things but the relative improvement is prodigious.

Moving on to more taxing applications, power consumption while video encoding with TMPGEnc was on par with the i7-3770K but the Haswell combination was modestly more power hungry in our synthetic stress tests, but that was to be expected considering the i7-4770K's TDP is 7W higher. Still, the i7-4770K was more efficient than both the 100W A8-5600K and A10-5800K overall.

C6/C7 Sleep States

One of Haswell's features that has gotten a lot of publicity for its new low power states (C6/C7), mainly due to the question of power supply compatibility. C6/C7 can theoretically drop idle energy usage but the PSU needs to be able to deliver a 0.05A load on the 12V2 line, much lower than the ATX 2.3 specification. Many of the big PSU manufacturers have posted a list of compatible models on their respective websites for prospective Haswell buyers.

Another issue is it takes some time for the CPUs to enter these deeper sleep states (and sleep states in general) and often it's woken up by the O/S when it polls the system for updated data to keep everything running smoothly — this is something Windows 7 and previous versions are scheduled to do in a periodic fashion. Windows 8 is designed more efficiently in this regard, syncing up and performing requests on demand to keep the CPU idle for longer stretches. Given how the much maligned Windows 8 home screen is filled with constantly updating Live Tiles, this improvement along with C6/C7 is almost a necessity to prolong battery life of Windows 8 tablets and laptops.

Best to our knowledge, the lower C-states are disabled by default on most motherboards due to the relative lack of Haswell certified units. In the UEFI/BIOS of our Intel DZ87KLT-75K, the setting is located in the power settings labeled "Lowest CPU Idle Power Setting."

Power Consumption Comparison: C6/C7 Power States
EPS12V Power (DC)
System Power (AC)
System Power (AC)
EPS12V Power (DC)
H.264/MKV Playback
Flash Playback
TMPGEnc Encoding
CPU Load (Prime95)

Pairing our IGP test platform with a Seasonic X-560 and Windows 8 Pro, we saw very little difference with the lower power states enabled. The savings were slight, and as expected, only when idle and under light load (video playback). The draw on the +12V2 line was also lower which seems to indicate this is more than what would fall under margin of error. We wouldn't recommend anyone rush out to upgrade to a Haswell approved PSU, it's simply not worth the time and/or effort on a desktop.

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