Dreadnought said:
Well, right now I'm doing an experiment of how much my G5 is using of electricity. I love the idea that it's on 24/7, but also have a very high electric bill each year. I know the G5 has a power supply of 600 Watts, so with 2 procs crunching 24/7 it's using almost the 600 Watts. So now I have the G5 on for a week and I check the meters in my fusebox. Next week it will only be on for 6 hours a day, when I'm home in the evening. I'll report my findings next week!
Well, unless you have 6 15,000 RPM SCSI hard drives in there, you are
NOT using 600 Watts. In fact, no matter
what you have in there, you're not using 600 Watts. The Watt rating on a power supply is its maximum possible load. NOT the actual power usage of your computer. For a while, I had a dual-processor PC (Dual 900 MHz Pentium III Xeons, as a matter of fact, with two 10,000 RPM SCSI hard drives, and a high-power Radeon,) with a power supply that was rated at 500 Watts. I ran a 3D intensive benchmarking app on 'loop', and after one hour (and all the temperature readings at a stable maximum,) I used an Ammeter to measure the load. I was consuming about 250 Watts. Idling, I was at about 100 Watts.
According to Apple System Profiler, my 2.0 GHz MacBook Pro in 'max saving' draws a measly 12.1 Watts, and under full load (Xbench, iDVD showing a complex menu, QT Pro compressing an H.264, I even plugged in two bus-powered USB hard drives, and a bus-powered FireWire drive, had the iSight going, AirPort connected, three Bluetooth devices, and screen at full brightness.) it draws a whopping 52.6 Watts. Yet it's 'power supply' (brick) is rated at 85 Watts! In the case of a laptop, it makes sense, you want to have enough extra power that you can charge the battery even while the computer is under 'full load'.
But on a desktop, you have to have all that extra power because you don't know how much power all the plugged-in accessories will draw! (Such as drives and cards.) It doesn't mean you're ACTIVELY USING all that power, it just means that it is available should you need it. (That's why an iMac G5 only has a 180 Watt power supply, even though a single-processor (with similar video card) Power Mac G5 still has the 600 Watt power supply. Because they KNOW the iMac will never need more than 180 Watts. That means that a single-processor Power Mac G5 probably uses no more than 150 Watts unless you have some seriously nasty power draining devices in it.