If you look at the spec sheets for the S479 motherboards, they generally only list support for Merom and Yonah; the Asus N4L-VM DH is an exception and lists Celeron M 4xx chips.
I can confirm that the Gigabyte & Abit S479 boards also support Celeron M 4xx, as do at least some of the Aopen boards. This is with the current BIOS releases; I’m not sure about previous versions.
Even though the Celeron M series do not support Speedstep, it isn’t proving that much of a penalty in the power consumption stakes. Here’s a comparison that I ran on the following system:

Abit iL-90MV, 1GB DDR2-533, Seagate Momentus 5400.2 120GB SATA, PicoPSU, EPS 55W 12V power brick.

Celeron M 420
Idle - 1.6GHz, 1.216V – 24W
Load - 1.6GHz, 1.216V – 28.5W

Core Solo T1400
Idle – 1GHz, 0.95V – 20W
Load – 1.66GHz, 1.1V – 26W

Core Duo T2600
Idle – 1GHz, 0.95V – 22W
Load (1 core) – 1.66GHz, 1.05V – 32W
Load (2 cores) – 1.66GHz, 1.05V – 36.5W

The Core Solo and Core Duo have a FSB of 667 and a L2 cache of 2MB versus 533 and 1MB for the Celeron M. The load figures were measured using Prime95.
The Core Solo and Core Duo were multiplied reduced to get as close to the Celeron M’s 1.6GHz as possible.

It’s surprising to see how inefficient Core Duo is when only a single core is running at full load. The second core must be consuming quite a bit of power whilst doing nothing. This seems to be confirmed by the fact that the second core only consumes an extra 4.5W at full load compared to idle.

The downside for Core Solo is that it is priced almost the same as Core Duo.
The Celeron M 4xx series has a list price in the UK starting at £35 compared to ~£135 for Yonah/Merom. Core Solo and Core Duo chips are available on eBay for much less than this, it’s too early for Merom to be appearing on eBay at friendly prices.

For those of you wondering why I’m posting so much data on low power computing on SPCR, please read this thread which I started today.

I've always thought the Celeron M would make a good desktop CPU. I had been planning to use my Celeron M 350 (1.3GHz) with an AOpen i915GMm-HFS for an HTPC. But the AOpen is getting hard to find now these days. Plus I could get a motherboard and Sempron CPU for less than just the AOpen motherboard.

Are your numbers all stock voltages? They appear to be. One advantage the Core Solo/Duo have is that you can use software to undervolt and reduce power. Unless you have a MB that can undervolt, the Celeron is stuck at it's stock voltage.

The Celeron M voltage is stock. The Core Solo/Duo were undervolted with RMClock and tested for stability with Prime95. I only tested for roughly one hour, so it’s possible that the voltage will need to be bumped up a bit for 100% stability. Or even lowered a bit actually for Core Duo, as I didn’t push it that hard.

I think the Yonah Celeron Ms are interesting because the boards that support them are getting cheaper and the CPUs themselves are very cheap. I bought my Core Solo from eBay for about 40% of the retail price. It was new and boxed and you will find plenty of bargains on eBay for mobile CPUs.

Smilingcrow, I want to thank you for your efforts in this area. I am figuring out what hardware to use as a pfsense firewall and am currently leaning in the direction of a S479 solution. For my application CPU power is not critical (though I need about P3-800 at a minimum), so with a Celeron M, if it consumes a reasonable amount of power at idle (where it'll be 90 % of the time), I can save some $ over a Merom or used Yonah Core Solo/Duo.

For reference, because of this application I am looking for a board that has 2 PCIe based GigE controllers and 1 FE with LAN chips well supported by FreeBSD (Intel is preferred). The best candidate to date is this Tyan board which seems to be just coming on the market: http://www.tyan.com/products/html/tomcati945gm.html. For this application I especially like that is has a version with a CF slot, so one could go completely without a HD for the most reliable headless system.

smilingcrow-

Thanks for the great work in this area. Is it possible to overclock at all with RMClock? I was thinking about getting a Core 2 Duo Mobile chip instead of the desktop for added power savings.
Does the speedstep still work if you adjust the voltage or FSB?

Cheers,
Chris

Thank you both for your appreciation.

I don’t think so. It’s possible that you could over-clock with Clockgen or a similar program provided that they support the clock generator that this board uses. I don’t think you’d be able to overclock much though, as all the busses would probably be increased which would likely be a limiting factor.
The Asus S479 board offers limited over-clocking as do so some of the Aopen boards.

Yes it does if you adjust the voltage or change the multiplier range in use.

Hello smilingcrow, do you still have the Abit system? Could you please check in intel TAT which C-States are used during idle?
Also, have you tried Clockgen in the mean time? My Gigabyte GA-8I945GMMFY-RH has an incompatible clock generator.

Very nicely done.

One limitation of the Yonah chips is that Intel has made it impossible to undervolt below about .95v. I wonder what idle wattage you'd get with Dothan's which readily undervolt to .70 with a 6x multiplier. (I currently have three desktop systems that do so--two with 400MHz FSB and one with 533MHz FSB.)

Smiling crow, I'd like to build a system like yours (actually I already have a yonah and MSI board) but looking at the RMclock utility, I don't see an option to change the voltage - do I need to purchase the registered version?