OT - Monitors - TFT v. CRT

[Dave Liquorice]

40W for 24/7 is around a unit/day or about =A322/year...

Well the PC is going to be on regardless, now I could possibly tolerate my percieved short comings of an LCD display if it offered a decent power saving over a CRT but they don't.

Anyway my PC doesn't take a couple of hundred. It takes around 100 mostly for the CPU, though the video card must take a bit has it runs at 60C with a fan...

It's not a empty box either, 1GHz Athlon, Ultra 160 SCSI controller, SCSI CD-RW, SCSI 18G HD, 2 Network Cards, 1 ISDN card, 1 dual port serial, 1 4xAGP video, 256M of memory (I think). Plus all the normal on board stuff, floppy, IDE, 2 USB, 2 serial, 1 parallel.

[Christian McArdle]

Don't be fooled. The 200W PC power supply rating is just like your consumer unit being rated at 100A. It doesn't mean it is actually eating it all the time. Whilst idling, a modern PC uses a tiny fraction of this. Even less if it turns off the hard disks after a period of inactivity.

Many of the components of a desktop PC are similar to those of a laptop. That runs for hours off a little battery. OK, the desktop versions are usually a more power hungry, but not by that much.

Christian.

[Grunff]

No, really - my PC takes a couple of hundred W. Trust me on this one. ;-)

[Christian McArdle]

What have you got in the thing?

Christian.

[Grunff]

Depends which one you mean, but the hungriest one has a 2.4gig athlon (about 90W), 2 hard drives, and a GeForce 4. Not particularly high spec, but easily eats 200W when running.

[Grunff]

Doesn't spend a great deal of time idle!

[Christian McArdle]

But, we're talking about when idle.

Christian.

[Christian McArdle]

Even at 3am? Is it some sort of server? Do you run SETI?

Christian.

[Grunff]

Funnily enough, 3am is backup time, which takes about 2 hours!

But the monitor's off then :-)

No, this one isn't the server - the server is a very modest

600MHz machine which probably does consume a mere 100W or so.

[John Laird]

The Seagate Barracuda 80Gb drive I have in my PC consumes a whole 13W when active, and your cpu is spec'd at under 70W. Have you upped your bus speed to 600Mhz or something, or is your graphics card a real hog ? (Still would expect it to not be using much power in a quiescent mode, though - why have graphics work no-one can see...)

[Grunff]

The graphics card is ~20-30W IIRC.

But at idle the monitor's powered down anyway, so surely if the comparison is to determine the significance of the monitor's consumption, then we need to look at consumotion with the PC running and outputting graphics?

Say it breaks down like this: CPU: 70W Graphics: 30W Motherboard: 10W All other cards: 5W

2x hard drives: 30W Losses in PSU: 30W (there's a very good reason it has it's own fan!) 2x case fans, cpu fan: 10W

Total: 185W

[Sparks]

This is possibly peak requirements?

The case fans must be pretty hefty to be sucking that much power... I have an 80mm one in fromt of me, it's only 0.14A (1.68w)

The most reliable way to see would be to actually measure it!

Sparks...

[The Natural Philosopher]

Frying chips?

Seriulsy, POC's don't 'idle' - they are either more or less shut down with teh clock stopped, or running at teh same curent they always run at. About 50-200W depending on things like what cards are in them and how many disc drives are permanently rotating.

CPU typically takes a few amps on its own.

[The Natural Philosopher]

Computers don't idle.

[The Natural Philosopher]

There is no difference between a CPU rushing around in a tght loop and exrecising a full blown compile.

The only thing that opoerartion affects is sometimes disc stepper motors under high disc access. Otherwise a PC is a constant load device, no matter what it is doing.

Unless its switched off.

[Christian McArdle]

Yes they do.

Christian. (BEng Electronic and Computer Eng.)

[Christian McArdle]

Not correct. The standard transistor types in a computer consume power when switching to overcome latent capacitance, but have low quiescent currents when not doing so. Modern computer equipment is specifically designed to slow down and avoid switching unnecessarily, meaning that power consumption drops when nothing much is happening. The power consumption drops markedly when you have idle CPU cycles.

It isn't like the old TTL logic, where the has to be constant current flow through a resistor, making the power consumption pretty constant, or related to state.

Christian.

[Christian McArdle]

There is some difference, as a tight loop won't lead to many state changes. However, only very old operating systems run the CPU in the tight loop. Almost all operating systems will put the CPU into idle if there are no threads demanding execution, giving even greater power consumption drops.

This hasn't been true for about 10 years.

Christian.

[The Natural Philosopher]

Well, you mena stepper motors don;t draw current these days?:-)

As far as CPU idling goes, only laptops seem to bother to do anything when the computer is not actually being tapped upon.

After all, the screen stll need srefreshing, the RAM all needs refreshing...the sort of 'lets slow down the CPU clock speed and RAM refresh rate until someone hits a keyboard' kind of thing costs money to implement...and lots of people myself included simply leave th bloody things on because parise be to microsnoit, they take too long to boot anyway...and they poll things like mail servers, and ther are other background tasks running all the time on a PC.

In short, depsite accepting all your points about switching speeds etc etc I still maintain that PC's in practice don't Idle.

MA Electrical sciences, Cambridge :-)

[Grunff]

Don't! You'll summon IMM...