Like many I have a home server that's always on. It does mythtv serving, email, mysql, usenet, dns, print server etc. But being always on, it burns watts even though it will be idle most of the time.

Watts matter because in California, at 31 cents/kwh, over the 3 year life of a system, each watt costs $8. For a 100 watt system the power costs more than the whole machine. Yikes.

So I want to build something that has decent power, but minimal wattage, at least when it's not doing some burst high-CPU activity.

It seemed like a mobile CPU like the penryn or merom might make sense, but I don't see many motherboards that have things I want and need. Like two ethernets (or a spare PCI slot for a 2nd one.) And 4 SATA or even 2 IDE for a 3-disk RAID. Or more than 2 memory slots (though I will be willing to compromise here. I need 3 PCI slots for video tuner cards, another for 2nd internet, though in a pinch I can do that via USB, or even buy USB video tuners (at a cost.)

No gaming, and the video will normally not be used, except as a spare workstation when needed, so onboard video or a cheap low power video card are good choices.

The VIA boards are low power but too underpowered. They will get swamped doing mythtv transcodes or commercial eliminations and other server tasks I do. The new Intel Atom looks interesting but all the motherboards for it are very limited -- few disk ports, sometimes just one memory stick.

So some options are the new 45nm Core 2 duos like the lower end 7200. Not super low power but lower than older systems. I can get mobos to do all I want for this.

Other options are an underpowered system, probably without RAID or enough slots for the video cards, requiring me to buy new USB based tuner cards for mythtv. If I do that, and go all USB (2nd ethernet and video) then a used laptop, or stripped laptop may make sense. Or does it make sense to buy a laptop mobo and put it in a real case to use regular drives? May also have to give up on raid-5 thoughts in this plan, as usb is too slow for disks.

Any advice or other options I have not thought of?

Might want to take a look at the new 65W Phenom.
http://www.tomshardware.com/review [...] ,1935.html

I've been looking to do exactly the same thing (always on mythtv home/server).

Based on advice from here and other forums I decided to go with AMD, since it's cheaper and lower power and will be more than enough for me.

Here is the parts list I am thinking of:

Antec Solo
Sparkle SPI250EP 80+ 250W PSU (lowest power 80+ psu I can find, should be 80+ all the way down to idle for this system which I think will be ~50W)
Biostart TA690G mobo (only AM2 board I can find with integrated s-vieo out and its cheap!) If you don't need that you could get a full ATX board with more features, like one based on the 780 chipset but I think they use more power.
AMD X2 4850e, 45W
WD Green Power 500GB
Hauppauge WinTV Nova-T 500 Dual DVB PCI card

Anyway hope that gives some ideas.

Ok, that's news to me. All the reviews I was seeing of Core 2 Duos vs. Amd X2s and Phenoms had the Core 2's several watts better in power. More expensive, but actually cheaper due to the power.

Now be clear, what I care about for an always on server is a mix of about 95% idle power and 5% peak power. More cores are bad unless it shuts down all but one core when idle for any period (which I presume they do.)

The Phenom remove pointed to above shows this -- Core 2 quad at 11 watts idle, vs. 22 watts for phenom, slightly better results at full load, but the core 2 still better than most of the phenoms.

Now I don't plan a quad core. The power load is higher and most of the stuff I will do won't be able to make much use of it. Dual core you can get lots of use of, and it's more future proof than a single core chip.

The whole system numbers are more balanced, presumably the intel support chips are worse than the AMD there. The 9100e looks like it would be slightly better than the Intel if I have a lot of load, but since it is reportedly slower, you would have the load for longer, losing the benefit, would you not?

So why are you guys recommending AMD?

Looking at this chart here: http://www.legitreviews.com/article/690/13/ and many other charts like it, it seems the E7200 is the chip for me, and it's only $130. IF I want to build a system based on a full-fledged top chip.

However, I was hoping for suggestions on what to do in the much lower power range, such as laptop chips, or possibly via or geode though they seem to not have readily available motherboards with any of the things I want -- memory slots, disk ports (PATA or SATA) and PCI slots numbering more than 1. I wondered if people here knew more about them.

Once again, $8 per watt over a 3 year life. So a 100 watt system eats $800 of power. Turning it into a 40 watt system justifies spending at least a couple hundred extra bucks.

I have a WD green drive and it's pretty nice if not super high perfomance. Can still hear it seek, which I had expected better on, and it doesn't accept the "go into low acoustic mode" command so it presumably already thinks its quiet. The saving here is 2 to 3 watts per drive, or $16 to $24 over the life of the drive, which is not as much of a driver, though it is greener.

An efficient power supply is probably worth it, though.

I'm not an expert but like I say from the feedback I'd received so far the consensus seemed to be that Intel was more performance per watt but if you just want cheap low power then amd was the way to go. It's hard to find wattage figures for the intel cpus though.

The AMD's I'm thinking about are 45W so will be alot less than the Phenom and probably most of the X2's you have been looking at. There is apparently a 35W part (from the AMD site) but it doesn't seem to be available retail.

Anyway still be interested to hear from someone more authoritative - I'm in exactly the same boat in terms of power cost (probably closer to $.40 kwh here in the UK) although I think an Intel system will probably end up too expensive for me.

Might want to go for a pico 120W PSU which will be more efficient at the wattages your looking at.

Also you might get more help at the forums at silentpcreview.com.... There's lots of info there.

Just looked at the graph you showed...

Obviously the E7200 is the lowest power there - but at 120W it can not be considered a low power system! If you need that kind of horsepower than I guess thats the best you can do, but from what you say you need it to do I think the AMD should be fine.

Like I say for my system I'm hoping for a well sub 50W idle state - maybe around ~35W (although it will go up when I add disks and such, and obviously woud be a bit higher with your extra PCI cards). A look on silentpcreview forums where people post their results will show this isn't unrealistic. So it's not really in the same league as the 100W+ idle monster systems your looking at.

Obviously it's up to you whats more important....

Here:
http://www.tomshardware.co.uk/amd- [...] 30798.html
toms hardware compare power consumption of 35 AMD processors...

You can see here that the 4x50e series draw 7W at idle... pretty good I think:
http://www.tomshardware.co.uk/amd- [...] 798-7.html

They seem to focus a lot on the difference between cool-and-quiet and not having it - but its still interesting.