Underclocking Question

By Savage1701
Apr 1, 2009
  1. Yeah, kind of unusual I know, but I have a situation where I need to know if I can save a significant amount of wattage by underclocking an older 478 CPU

    I have a couple of old Asus P4-C800E-Deluxe boards with 3GHz 478's on them. I use these strictly as servers to grab OTA HDTV signals via tuner cards and BeyondTV front-end software.

    I am also making the following assumptions: The CPU and Hard Drives draw the most power. The CPU is not really needed because the tuner cards don't really do anything but strip the carrier wave away and send the .TS data stream to be recorded to the hard drive. Finally, using suspend or standby is not really an option, as BTV is not able to reliably bring the hardware out of resting mode to start recording a show. Finally, the systems function fine on old 5200-series AGP graphics cards as they don't handle any real decoding chores. I think I am about as stingy as I can go in the graphics department, as PCI-based cards are not an option.

    Now, I assume that all other things being equal, a 500GB HD needs about the same amount of wattage to run as a 1 or 1.5 TB drive. I am pretty much maxed on HD size at this point. But, if I underclocked my CPU by say 50%, would I net much in the way of energy savings, or not?

    Also, do all power supplies draw some base amount of wattage when they are turned on, regardless of the load presented to them?

    Any info would be appreciated.
  2. Tmagic650

    Tmagic650 TS Ambassador Posts: 17,233   +234

    "But, if I underclocked my CPU by say 50%, would I net much in the way of energy savings, or not?"...

    I would say not
  3. redk

    redk TS Rookie Posts: 91

    You could underclock and underVOLT and get a slight bit of savings, but the chips are high wattage, so...
  4. Technochicken

    Technochicken TechSpot Paladin Posts: 729

    No, they only draw what your computer is consuming. You could save energy by upgrading to a more efficient power supply though.
  5. Savage1701

    Savage1701 TS Enthusiast Topic Starter Posts: 153

    It worked like a charm with Pentium D series

    Well, just for the heck of it I put an Pentium D 940 system on a watt meter. Averaged about 200 watts draw over 5 minutes at STOCK cpu speeds. I then rebooted, went into BIOS and turned the clock down from 400 to 100.

    Did the computer move more slowly? You bet it did, but more than fast enough for its intended use.

    The real benefit was that my watt meter now read about 150 watts draw after boot-up and just sitting there. I'd call that a substantial savings.

    I'm not saying it's for every CPU out there, or that it's going to help the newest low-power CPU's, but I've got a great Pentium D 900 series system laying fallow that I can now put to work as a video file server and it uses far less energy than the 250 watt P4 socket 478 system it's going to replace.
  6. CMH

    CMH TechSpot Chancellor Posts: 2,039   +9

    I must say that that is a very interesting find. I've always believed that underclocking should come up with some significant power savings, but finding hard evidence for this (don't quote me about evidence strength here lol)

    However, I believe this is true especially in your case because of the high power draw of the Pentium D 940 to start with. It would be interesting to see if underclocking an already low power draw CPU would bring about the same result.
  7. Savage1701

    Savage1701 TS Enthusiast Topic Starter Posts: 153

    CMH - Yes, I wonder if a low-power CPU would yield the same results. I somehow doubt it. And my desire to underclock is probably rare. I am only doing it to recycle a CPU that needs very little horsepower to accomplish its tasks.
  8. CMH

    CMH TechSpot Chancellor Posts: 2,039   +9

    I can see why you'd want to save some money and recycle an old CPU/MB/RAM/etc.

    I was thinking of the same, until I thought I might save more money, and get better stability, which was why I bought the lowest power consumption parts for a new comp....

    Cost me 250 bux, and hopefully in the long run, the savings on my electric bill would be more than this. Especially if I underclock it, which is why I'm hoping someone will try this on a low-power system XD

    BTW, how'd you SAFELY measure your power draw? Mucking around a computer is pretty safe, but when it comes to mucking around with mains power, I'm quite reluctant....
  9. Savage1701

    Savage1701 TS Enthusiast Topic Starter Posts: 153

    Safely Measure Power Consumed

    CMH - No magic or danger really - just bought one of those Kill-A-Watt power meters. Plug it into the wall, plug whatever your want to measure into it. VA, instant watts, watts over time, cost (if you enter your KwH cost), etc. It's a great way to know what's contributing to your electric bills, such as LCD's that draw 9 watts even when they are "sleeping"...

    Now, is it sensitive enough to measure if you add a stick of RAM? No. But it will detect if you add or subtract a hard drive or 2.

    Once the CPU had booted up under regular and underclocked situations, power drawn held steady at about 200 watts regular, 150 watts underclocked on the AC line. No other configuration changes were made to the CPU and it was set NOT to enter sleep mode or anything like that, since that would screw up its intended use as a BeyondTV server.
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