POWER SUPPLY

The original home computer - the IBM PC - (released in 1981) had a bulky 63.5 watt power supply. It would power that basic PC but had too little power to accomodate any expansion. Which was fair: expansion wasn't available. The original PC had a single 5.25 inch floppy drive and no hard drive. About the only expansion IBM offered was a second floppy drive. That was it. It is amazing today to know that IBM sold a jillion of these very basic boxes - almost unchanged and with no expansion capabilities - for almost 6 years.

Power supplies today are pretty well standardized for normal cases. There are some variations in their power output (wattage), and some minor differences in the power jacks (or lines) that come out of them, but they're pretty much all the same size and shape. They are attached to the back panel of the case frame by 4 screws.

One end of the metal box that contains the power supply has the threaded holes for the 4 attaching screws, a grilled cooling fan opening and the male plug receptacle where the power cord plugs in. Usually it also has a female receptacle where a special cable can be plugged in to power a monitor, should you choose to. That was used more on early versions of computers and is seldom used today, so the latest versions of the power supply are leaving this receptacle off. The other end of the box is where the clump of wires come out that connect to the parts inside the computer (including the mainboard) and supply power to them. It's also where the cable comes out that connects to the power switch on the front of the computer case.

The first really expandable PCs had fairly large (by today's standards) 200 watt power supplies. People quickly started adding more parts to their computers, so the power supplies had to get larger to handle the additional demand. It wasn't long before a 250 watt power supply was considered a minimum. Today there are many more parts attached to a modern computer than there were to those first PCs, but technology had caught up with modern demands and all the parts used in a computer are much more efficient than they were just a few short years ago. So today a 230 watt power supply is considered standard - and more than adequate for all but the most demanding user.

The two common types of power supplies used today are the AT and the ATX types. The AT type is what is in current use - it is in nearly all the tower type cases in use today. The ATX type power supply is the new standard - it will be used (and is now being installed) in all new computers. The newest (ATX) power supplies allow almost total control of the power supply by the mainboard, so now programs are being written (many are already in place) that allow the computer to become much more energy efficient. The newer ATX type power supplies require a redesigned mainboard (with different power plugs), so they are not an upgrade to the older AT type power supplies - they are an evolution. In other words, you can't replace a bad AT power supply with a newer ATX power supply - the power connectors wouldn't connect to your old style mainboard - you've got to replace like with like.

Probably the most common computer hardware failure is the power supply fan. That makes sense when you think about it - it has moving parts that spin every second you have power to your computer, so it's more active than anything else in your computer. O.K., you also have a smaller fan that cools your CPU chip - and I guess you could make a case that it is just as active - so let's just say they're both the most active things in your computer and they both head the list of the most frequent hardware failures. If your power supply cooling fan fails (locks up or starts making a horrible squealing sound), it can be replaced. It's not a real difficult job and the fans are available at major computer stores (CompUSA, for example) or your local Radio Shack, if you should want to attempt it yourself. If you do, be sure to take all electrical safety precautions and carry your old (dead) fan with you when you buy a new one - there is some variation in connectors and fan sizes. When your fan quits, you have no choice but to fix (replace) it or, pretty quickly, you'll be replacing the whole power supply anyway.

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