I recently came into possession of an i7 4790 basically for free, so I swapped out the 4590 in my HTPC to get a little extra oomph and longevity out of the system.
It is installed in an Asus B85M-G motherboard. The board is currently running the "Version 2001 2014/06/17" BIOS.
I have read about certain features being removed from various Haswell BIOS versions due to a microcode update. Namely, the ability to force a CPU to run all cores under load at its max turbo frequency. This CPU will run at 4Ghz when one core is loaded. So far, no matter what settings I choose in the UEFI, the most I can get it to do is to peg all four cores at 4Ghz when idle, but when there is a load they drop to 3.8.
This UEFI has an absurd number of options for a non-Z-series board, and I've tried increasing all of the turbo power target and other related settings, but nothing seems to change. Its strange that it does run the cores all at 4Ghz when there isn't much of a load (if I set the minimum CPU frequency in Windows to 100% this behavior is more obvious). Running a single threaded benchmark allows all cores to stay at 4, with one periodically dropping to 3.9.
I don't have a "multicore enhancement" setting anywhere in my UEFI right now. I do have XMP turned on, as my memory does have an XMP profile and I've read that Asus sometimes will enable the max turbo setting secretly when enabling XMP.
Does anyone know if I'm just missing something or if this is impossible for some reason? I want to update the BIOS (there are several newer versions) but I don't want to risk some irreversible microcode update if there's a chance that I've just overlooked a setting. Its possible that this board has already HAD such an update and its already too late, but I'm just not sure. Every picture or thread I've read online has completely different information because there are hundreds of similar boards with slight variations in settings and they change with every BIOS update.
Thank you!