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I have been reading up on Intel's new Haswell processors, and it seems that the K-series is designed for overclocking. But what if I want to underclock? Do I still need to buy a K-series processor?

I'm interested in building a system with minimal power drain and low noise. Is there any point in underclocking (and do I need K-series for that), or can I rely on the built-in power saving features to deliver on a system that will be 99% idle?

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If you are that bothered about power consumption, buy a "T" version CPU rather than a "K" version - the maximum power consumption is typically 30-50% lower but performance is obviously reduced. Noise could be reduced by using liquid cooling instead of a fan. Alternatively, consider an Intel Atom or AMD Fusion CPU as they use even less power and have limited cooling requirements. You haven't specified what you are using it for so it is hard to say if such a system would be powerful enough. – James Oct 2 '13 at 8:59
@paddy Only the K series will allow you to change the required values that makes underclocking and overclocking possible. – Ramhound Oct 2 '13 at 11:16
I'm essentially building a Linux NAS box to replace my current one which I also use as a windows domain controller, as well as for development, subversion, firewall... Tossing up whether to forget about those conveniences and just get a real NAS. – paddy Oct 2 '13 at 11:25
@Ramhound Are you sure? I thought the only difference with the K version was that the upper multiplier limit. – David Schwartz Oct 2 '13 at 13:05
@DavidSchwartz - Intel has taken effort to disable the ability to overclick the non-K products. The same properties that need to be adjustable to overclock are required to underclock. I would agree with James simplying buying a low powered product is better the underclocking a high(er) powered product. – Ramhound Oct 2 '13 at 13:30
up vote 1 down vote accepted

I suppose it might depend on how finicky you want to be. If money is any object, I doubt the K series pays off for you .vs. buying a processor where power-savings is a built-in optimization, at some loss of ultimate performance - which you'll be losing anyway with underclocking. The first "K" processor to show up in cpubenchmark's power/performance chart is a LONG way down the list.

Most serious power-savings-nerds in the NAS arena use an Atom, from what I have seen. On my 24/7 router builds I opted for (pre-haswell) i5-3470 on bang for buck while still having bang - those systems typically use (measured) 30-50W to run (500W bronze power supply, 3 fans running with MB speed control, full size case.) Plenty of folks use an Atom in that job, too - for me, that's "low enough" and leaves headroom for some things I want my router/firewall to have headroom for.

I decided I wanted to use ZFS for my (bsd-ish) NAS and also that I wanted to spend a bit less on the box, at least for the first try at it, so I got an old rack server for cheap. It's noisy and hot, running around 100 watts (two xeon processors and those obnoxious 1-U server fans, which are noisy powerhogs themselves) However, most of the time it uses 7-8W - it's Wake-On-Lan capable, and when it's asleep, that all it draws.

If you are not using ZFS, an Atom appears to be more than sufficient, and some folks are managing limited ZFS deployments with them (with some of the more drastic ZFS processing/memory hogs, eg prefetch, turned off.)

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I didn't know about ZFS, so I'll look into it. On my old Pentium 4 server, I just use ext4 on a software RAID-10 with Slackware. ZFS's RAIDZ sounds interesting. Tempting to have a play with it. If I end up chucking my new disks into a HD ProLiant Micro Server, I'm sure there'll be enough grunt to run ZFS. – paddy Oct 3 '13 at 1:34

The standard Windows Balanced power plan works pretty good since Windows7. Windows 8.1 has some improvements in processor driver. at least for all modern Intel processors. Also you can tweak the standard power scheme using Rightmark PPM Panel.

try more aggresive increase P-state policy (rocket), and more lazy decrease P-state policy (single).

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