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programming and human factors
by Jeff Atwood
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I recently built a new, much lower wattage home theater PC using the Pentium-M processor. The P-M was, until very recently, a mobile-only part. And that's why it's ideal for HTPC duties-- it offers very high levels of performance at an astonishingly modest power draw. For example, per these system power consumption measurements at Tech-Report:
Pentium 4 640 @3.2ghz
125w idle, 211w load
Pentium-M @ 2.4ghz (overclocked)
92w idle, 107w load
So the P-M system consumes 35% less power at idle and 97% less power at load-- while offering comparable performance. The Pentium-M is much more efficient per clock, so it doesn't need to run at exorbitant clock rates. There's a direct correlation between power consumption and heat/noise. The cooler a system runs, the quieter it will be. And quiet is what you want for a HTPC.
In my bench testing of the Pentium-M 1.6ghz, the large, fanless Alpha heatsink never exceeded 50c under Prime95 torture test load, even when left running overnight. And that's totally passive, with virtually zero directed airflow! Try that with a Pentium 4 and you'll create your own personal China Syndrome. Because the P-M runs so cool, I was able to get away with using only two fans in the final system-- the power supply fan, and a dramatically undervolted 60mm exhaust fan:
See the three hard drives in there? Two are mounted under the DVD-R. Here's a breakdown of all the parts.
Core system
Storage
Case
Expansion cards
The AOpen mobo offers voltage and bus speed controls; I undervolted the P-M from ~1.3v to ~1.1v, and overclocked it to 1.7ghz. This system, as measured by my trusty Kill-a-Watt, consumes 72w at windows desktop and 81w in Prime95 torture test. Now, that's power draw from the wall; due to inefficiencies in all power supplies, some of that power is immediately lost as conversion heat inside the PSU. A typical power supply is about 70 percent efficient, so the actual power consumption inside the PC is closer to 50w idle / 57w load. Pretty amazing for a fully loaded 1.7ghz PC that performs like a Pentium 4 2.6ghz.
When building a quiet PC, pay close attention to the hard drives and video card you use:
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I was thinking about building almost exactly the same thing - Media Center based quiet PC for the living room. Since I have Pentium-M based laptop, I know exactly how cool it runs under normal circumstances -- I am very impressed by it's performance/heat ratio.
Btw, how much did all of this cost?
> Btw, how much did all of this cost?
Hard to say, since more than half of it was inherited from my old HTPC. The i855 mobo + 1.6 ghz CPU was kind of pricey at ~$400, but IMO well worth the cost for that incredible performance/power ratio.
Off the cuff, I'd say you'd need to spend around $800-$900 to build a HTPC system up with most of the parts I've enumerated (maybe one hard drive instead of three). It can certainly be done for less, if you don't care as much about noise.. but these parts are all hand-picked for the best performance/power ratios and thus cost a bit more.
Jeff Atwood on February 24, 2005 12:03 PM> It can certainly be done for less, if you don't care as much about noise..
I care very much about the noise, that's why I'd like to go this route - fanless processor cooler, same for chipset and GPU.
I completely overlooked the fact that you listed three (!) hard drives. What's the point? RAID configuration or as much storage as possible at the best price (160 and 200GB models should be the cheapest now)?
>you listed three (!) hard drives
Noise! There aren't, AFAIK, large hard drives with the same ultra-low noise levels of the spinpoints. And Samsung has yet to introduce anything larger than 160gb for whatever reason.
Jeff Atwood on February 24, 2005 12:38 PMTalking of hard-drive noise while building a HTPC I started off with a 2.5inch IBM laptop drive, thinking it would nice and quiet. However it was the largest noise maker in the whole system. It was a very old model from an old laptop I had.
Switched to a new Seagate with fluid bearings etc. and it's really really quiet, can't hear it from more than 1-2 feet away.
How noisey is your PSU? Thought of getting a passively cooled PSU? For example:
http://www.mini-itx.com/store/?c=10#p1806
I've built a HTPC using an EPIA mini-itx board which means I can use one of these 55W passive PSUs, and get a $15 passive heatsink for the VIA CPU.
So the only noise is from the pretty quiet hard-drive.
EPIA system is pretty low power, power consumption wise but also CPU horsepower, but fine for running basic MCE 2005.
Sean McLeod on February 25, 2005 04:01 AMExcellent - I've been waiting for you to blog about this since you mentioned you were building a P-M HTPC a few weeks ago. I will get round to building a very similar machine in a couple of months time - thanks very much for the insight on quiet components etc.
Out of interest, do you have any performance issues with it yet? I was thinking of building a very similar specced machine to yours, but a friend of mine recently put together a Media Center PC and spent in excess of £800 (approx $1500) on it - he had a really high-spec machine. Do you really need a kick-ass machine to decode DVDs and record tv?
> Do you really need a kick-ass machine to decode DVDs and record tv?
No, because the hauppauge card is dedicated hardware for the really difficult part -- realtime MPEG2 encoding.
Anything around 2.0ghz or 2000+ is more than adequate for HTPC.
Now if you're transcoding lots of DVDs to DivX or other MPEG-4 formats, you might want more power. I still think a fast Pentium-M will be plenty good at this, though.. and the 2.0 P-M overclocks quite easily, if you're needing more performance.
Jeff Atwood on February 25, 2005 11:39 AM> EPIA system is pretty low power, power consumption wise but also CPU horsepower, but fine for running basic MCE 2005.
I don't know. I've owned two EPIA systems, one 533mhz eden, one 1ghz Nehemiah. I don't think I would be happy with the MCE performance of either machine. The Pentium-M is admittedly much more expensive but easily offers 2-3x the performance per clock of those chips at a similar wattage.
Jeff Atwood on February 25, 2005 11:44 AM> How noisey is your PSU? Thought of getting a passively cooled PSU? For example
I would, but the PSU is one of the two only fans in the system, so in this case I need the PSU fan to dissipate the ~25w of PSU conversion loss as well as the lion's share of the ~50w that the rest of the system is using.
The PSU is the loudest part of the system, but that's relative-- it's still a very quiet 80mm fan at lowish RPMs. I thermistor modified the PSU, eg, I moved the thermistor away from the heatsink it was mounted on so the fan almost never ramps based on temp.
Going to an external power brick is an option for lower voltage systems but I don't think I'm quite at that lowest of levels yet.
Jeff Atwood on February 25, 2005 01:01 PMA few small changes.
I dropped the Audigy in favor of the SPDIF bracket for onboard digital out. I had to buy it from the AOPEN web site for $15:
http://store.myaopen.com/aosco.html
I also switched the very hot running, older model of the PVR-350 I had with the PVR-500 which not only runs cooler (no heatsinks on either encoder chip out of box) but also has dual tuners. So you can record one channel while watching another, etc:
http://www.directron.com/wintvpvr500mce.html
Power usage is now at 67w idle, 76w Prime95 Torture Test. Prior to this it was at 72w/81w.
Excellent PVR MPEG2 encoder card roundup:
http://htpcnews.com/main.php?id=pvr_card_id_guide
Jeff Atwood on March 2, 2005 11:13 PMJeff,
I'm compiling the parts to build a system comparable to this (especially with the passive CPU heat sink) specced a bit higher (Pentium-M 2GHz, 300W PS, dual-tuner, etc.) and I have a couple questions about the specifics of how you built this:
What sorbothane products did you use to dampen the hard drives? I checked their site and it's much more than I'm used to seeing.
What's the loudest component in the system? I'd think it'd be the optical drive, but I'm interested to find out for sure.
About how far away from this do you have to get before you can't hear it in a quiet room?
What/how many case fans do you have running in there? I can only see two what-look-like-60-mm exhaust fans, but if there's a particular brand you used, I'd like to know.
Does the P-M have any thermal failsafe, in case your case fans fail or you get a bit carried away with stepping down the fans? Have you pushed it that far? I've read that the P4 has a two-level system (step-down, then shut-down), but I've seen nothing on the P-M.
Thanks.
Dan on May 5, 2005 02:07 PM> What sorbothane products did you use to dampen the hard drives?
I bought a sheet of 1/8" sorbothane from McMaster-Carr; I don't remember the exact dimensions but it was roughly the size of a standard sheet of paper
http://www.sorbothane.com/distributor_beta.html
It's AMAZING stuff. Truly unparalleled for vibration absorption.
> What's the loudest component in the system?
If in use, definitely the optical drive. If it isn't in use, the 80mm exhaust fan on the power supply.
> About how far away from this do you have to get before you can't hear it in a quiet room?
It's partially enclosed in a media shelf, primarily in the rear with sliding doors that stay open when I'm using it. Unfortunately I have to orient it left to right due to the space it needs to fit in, so the fans that SHOULD be facing the rear are facing the "left" which makes a big difference. I have eggcrate foam lined behind it to assist in damping. It's slightly audible from couch distance, but to give you a baseline-- I can hear the hum of my plasma TV over it. Pretty darn quiet.
> What/how many case fans do you have running in there
The two 60mms, severely undervolted using a Zalman Fanmate, and the one 80mm PSU exhaust.
> Does the P-M have any thermal failsafe, in case your case fans fail or you get a bit carried away with stepping down the fans?
Yes, it does; Intel always has superior thermal safeguards, so I wouldn't worry about this. The thing you have to worry about is frying the HDDs, as they are more temperature sensitive than almost anything else inside your PC. Oh yeah, and did I mention they have all your data too?
Jeff Atwood on May 6, 2005 02:15 AM> The PSU is the loudest part of the system
> Going to an external power brick is an option for lower voltage systems but I don't think I'm quite at that lowest of levels yet.
> 76w Prime95 Torture Test
At 76w you could use the following 120w fanless power brick.
http://www.mini-itx.com/store/?c=10#p1806
I see you are using a Pentium 4 Heatsink; I've read that P4 Heatsinks don't fit exactly on the P-M boards. Apparently the P-M sits a tad lower, so the standard P-4 HS does not connect with as much pressure, which is possibly OK.
Did you 'adapt' the Heatsink in any way?
Also - your case looks cool, being see-through and all, but an aluminum case would aid in head dissipation, I would think.
Chris S on February 11, 2006 05:45 PMOne simple improvement to reduce your power usage by probably 10W at idle and more at peak demand: Replace the PSU with a Seasonic SS-300SFD 80+. http://www.silentpcreview.com/article286-page4.html It never dropped below 80% efficiency even at just 40W load! Most other PSUs drop to below 70% at that low a power output.
A more cutting-edge option would be a PicoATX with a power brick -- it's only slightly more efficient, tho, and more fuss & $$. http://www.silentpcreview.com/article601-page1.html
Mike Chin on August 24, 2006 09:20 AMMike Chin from http://www.silentpcreview.com , ladies and gentlemen.. ;)
As usual, excellent advice. I think I'll go with the SS-300SFD as a drop-in replacement for the sparkle 180w PSU that's in there now.
> Also - your case looks cool, being see-through and all, but an aluminum case would aid in head dissipation, I would think
The construction of the case has very little effect on cooling, because none of the hot surfaces are typically in contact with the case. There are things like the Zalman 300A, however..
http://www.silentpcreview.com/article302-page1.html
Jeff Atwood on August 24, 2006 10:08 AMSomeone above was looking for an SPDIF bracket, but the other sites don't seem to carry it anymore. Anyways, I found another source here:
http://www.vidabox.com/shop/index.php?main_page=product_info&cPath=4&products_id=9
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From the site:
SPDIF PC / Computer Bracket for Digital Audio out. It has both Optical and Coaxial (RCA Jack) out. Works natively with most MSI motherboards, but also compatible with Gigabyte & others.
Pin out configuration:
Pin 1 - power (Red wire)
Pin 2 - signal (White wire)
Pin 3 - ground (Black wire)
Pins can be reassigned fairly easily if needed by pulling out pins from connector and resinserting as needed.
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The_BigSoftie on November 4, 2006 02:50 PM| Content (c) 2008 Jeff Atwood. Logo image used with permission of the author. (c) 1993 Steven C. McConnell. All Rights Reserved. |
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