You may be wanting to build a new PC, or upgrade the unit you have now. Since computers require more wattage than ever before, concerns about your power supply are sure to surface. The question "How much is enough?" has to be answered.

Fortunately, simple math, and the numbers I'll supply with this article, will answer your question.

The first item to consider is your CPU. Some of today's high end chips require 100 watts all by themselves. If, for instance, you planned on salvaging an older case with a 250 watt power supply, and wanted to base your unit on a Pentium 4, you better think again. You might be able to save that case, but the power supply will have to be replaced.

The reason is all the other items drinking electricity from that same little well. Your motherboard will only require 15 to 30 watts, making it one of the more economical components. But a graphics card, of 128MB or more, will require another 100 watts. Add a hard drive, at 30 watts, and you've used up your capacity. There will be nothing left for RAM, a CD/DVD, or any PCI cards you may require.

How much more will those items need? RAM has to have 7 watts per 128MB. So, a 1GB module means you'll need 56 watts. A CD/DVD ReWritable drive takes an additional 30 watts. Those PCI cards are 5 watts each. Add 20 watts for a floppy drive, and extra case fans.

The total for all this comes out to around 380 watts! A 400 watt power supply barely covers it. In fact, you would be well advised to get a 450 watt or larger just to be safe. Not having enough power can mean a fried computer. They have a distinctive smell, like burned money!

On the other hand, you can design a power miser, like I did in my book "Building a PC for Beginners". It requires a total of only 214 watts, allowing me to use the 300 watt power supply that came with the bargain case I bought. It was built using a Sempron chip, and a 64MB graphics card.

Michael Quarles is the publisher of Monkey See Monkey Do Books.