Monday, September 3, 2007

How much power does your PC actually consume?

If you have bought a PC within the last 2 years you probably have a 400W power supply. If your PC is just a few months old, you’re likely to have a 500W or an even higher rated power supply. Some state of the art dual core processor based PCs complete with two graphics card in SLI or Crossfire mode comes with as high as 1KW power supply units. But the question is: do we really require that much power?

A quick googling revealed that I was right. Computers rarely use that much of power. In the blog Coding Horror, the author describes his experiences when he built a computer, over clocked it, benchmarked it and did all sorts of geeky stuff. The configuration of the PC is mind blowing

Processor: Intel Core 2 Quad Q6600 Kentsfield 2.4GHz
Motherboard: MSI P6N SLI Platinum LGA 775
Graphics card: 2 x MSI GeForce 8600GTS 256MB GDDR3 (OC)
Memory: 2 x Kingston 2GB (2 x 1GB)
Hard disks: Western Digital 150GB SATA, Seagate Barracuda 7200.10 500GB
CPU Cooler: Scythe SCMN-1100 100mm Sleeve CPU Cooler
DVD Drive:LITE-ON 20X DVD±R DVD Burner

That’s a monster PC!! Now let’s see how much power it consumes.
He used Kill-a-Watt to determine the power consumption. Guess what? At the Windows desktop it was 130 watts and during the extreme CPU and GPU torture test it came to a paltry 220 watts. That’s even lower than the PSU units that used to come with the earlier Pentium 4s. They used a 550W PSU with their machine, so it was operating at 40% power even at full load.

Now that I came to know the actual power usage of the machine, I decided to test how much accurate the extreme power supply calculator was. I went to their site and entered the exact the configuration and hit "calculate" and it came up with 359W. This was a bit higher than the actual results but still much lower than you would have expected.

This wasn’t the only case of low power usage. I found another one at a forum.

This time the configuration was this:

Intel Core 2 Quad Q6600
Motherboard: MB IP35-E
Memory: 4GB ram (2X2GB)
Graphics card: PCI vid card
1 Hard disk
1 CD drive

The same Kill-A-Watt meter was used to measure the power. Here are the results.

Power at idle (Windows desktop) = 113 watts
Power at full load = 183 watts

Surprising, isn't it? If you are still skeptical, here is another one.

The PC:

AMD Athlon 3800+ 2.4Ghz processor
A very high end ATI graphics card (the kind with dual power connectors and lots of warnings about power requirements) * Does not mention the model
2 optical drives
3 hard disk drives
2GB of RAM

According to the author, the PC was at a constant 147 watt and when he fired up some program called Rhapsody (never heard that before) it jumped to 159 watt. You have to agree, that is a pretty decent configuration, not something you expect to run at 159 watts!!

So what did I learn from this? My PC and your PC too, does not require that monster power suppy unit at the back of the cabinet. The next time you buy a new computer for yourself or suggest somebody on a new configuration, remember that a very high rated power supply unit isn’t absolutely necessary. However, one thing to keep in mind is that most PSU operate best when it’s within 70% of the rated load. This means that when you buy a PSU make sure that the maximum power drawn by the PC does not exceed 70% of what the PSU is capable of delivering. If we do a little math for the computer I mentioned at the very first, you will find that with a 400W PSU the PC draws just 55% of the power (at full load) that it was designed to supply.

It's good to learn that even one of the most powerful configuration can run smoothly with just a 400W supply.


  1. tweaked (quite) a bit ... 55 watt INCLUDING my 14 inch LCD. no kidding. and it is not a laptop. it goes up by some 10 watts if processor is running full speed.

  2. This is not the whole truth. The power rating on your PSU is the sum of what the different transformers inside can supply, so don't trust it blindly.

    My PSU rated at 350W has this list on the side:
    + 3,3V / 22 A
    + 5V / 21 A
    + 12V / 18 A
    + 5V Vsb / 2.5 A
    - 12V / 0,3 A

    Pentium4 and AthlonXP and newer systems draw most of their power from the 12V-line.
    So the theres 12V * 18A = 216W that can be drawn from the 12V-line, which is where modern motherboards+cpus+gpus+harddrives pull their power from.

  3. can i get the approximate power consumed for
    1)pentium dual core E5500 @2.80GHz
    2)Installed RAM-2.00 GB
    3)1 hard disk
    4)1 CD drive

  4. Get an ampermeter and measure. There's a lot involved in a complex system.


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