The ASRock H81M-ITX does support adjusting multiplier ratios for K series Haswell processors. Oddly, this works in BIOS version 1.90, but not version 2.00. My boards came with version 2.00, and I had to downgrade to 1.90.
The four-phase VRM does make a small amount of noise and gets rather hot. There are no heatsinks on the switching MOSFETs. However, so far it seems to be able to supply enough power for moderate overclocking. I’m currently more limited by the ability of the stock cooler to cool ~110W of power.
- Core i5-4670K: 4.1 GHz, 1.12V
- Core i5-4690K: 4.3 GHz, 1.18V
- Core i7-4770K: 3.9 GHz, 1.02V
- Core i7-4770K: 3.9 GHz, 1.18V
- Core i7-4770K: 4.0 GHz, 1.13V
- Core i7-4790: 3.8 GHz (Auto), 0.98V (Auto – 0.05V)
- Core i7-4790K: 4.2 GHz (Auto), 1.16V (Auto – 0.04V)
- Core i7-4790K: 4.4 GHz, 1.125V
One interesting observation is that the processors that need less voltage to achieve a particular frequency also tend to be harder to cool (higher leakage?). Since my machines are limited by cooling (or power?) rather than voltage, I can’t make chips with low voltage run faster.
- Adjusting CPU Ratio with BIOS 1.90: Tested with Core i5-4670K, i5-4690K, i7-4770K, and i7-4790K
- Adjusting CPU core voltage
- When manual CPU ratios are used, voltage is set to highest bin instead of varying with CPU speed.
What doesn’t work
- No CPU Ratio adjustment with BIOS 2.00
- No BCLK adjustment
- No memory overclocking: Memory speeds are adjustable, but do not go above stock (DDR3 1600 MHz in my case)
- Core i7-4790: CPU ratio cannot be increased. Core voltage adjustment only in Auto+offset mode (no override). “Multi-core enhancement” does not function. (i7-4790 is stuck at 40x/40x/39x/38x)
- The ethernet port dimensions aren’t quite right (too big?). Ethernet cables disconnect when tugged or sometimes spontaneously, even when still latched properly. This is true on all 8 boards I have.