Power and Panel Cables and Connectors
The AC Power Cord
The cord that connects your computer to the AC power source has the distinction of being just about the only thing on your computer that has remained relatively unchanged since the early days of the PC.
It actually has a name, by the way: It's officially called a NEMA 5-15P to IEC-320-C13 cable. So have some fun. Go to a computer shop and tell them you want to order a NEMA 5-15P to IEC-320-C13 cable. Just don't blame me if they slap you.
Internal Power Connectors
PATA hard drives and most other IDE devices use a standardized, 4-conductor power connector like the one shown at the right, which is called a Molex or P5 connector. This connector is becoming a lot less common as SATA displaces PATA as the drive interface standard for desktop computers.
The connector is shaped in such a way as to prevent accidentally attaching it backwards, so don't force it. If you apply voltage with reverse polarity to an IDE drive for so much as a moment, you will permanently destroy the drive.
Floppy Drive Power Connectors
Floppy drives and some older CD-ROM drives and other IDE devices connect using an even smaller power connector called a P7, which is shown on the right. Although the connector is keyed, it's very easy to force it on the wrong way. Even a skinny-armed geek can do it. So if it doesn't slip on easily, you probably have it on backwards. Don't force it! Think brains, not brawn.
As with hard drives, if you connect a floppy drive's power cable backwards for so much as a moment, you will destroy the drive. So be sure that you don't have the power connector reversed.
SATA Power Connectors
And as if the existing assortment of power connectors weren't enough, SATA drives use yet another type of power connector that's specially designed to enable "hot-swapping" the drives.
If your power supply doesn't have SATA connectors (pretty much all new ones will), you can purchase inexpensive adapters that will convert a Molex connector to a SATA connector (or voce-versa, depending on which kind of power connector you're short of).
The main power to the motherboard is provided by something called the P1 connector, appropriately enough. The P1 connector is keyed to help prevent incorrect insertion and is held tight on the motherboard by a little plastic clip. If it doesn't fit, don't force it. You're probably trying to attach it backwards.
Never plug an ATX power supply into AC power unless the P1 connector is connected either to a motherboard or to a test load. Plugging an ATX power supply into AC power while the P1 connector is not connected to a load will destroy the power supply.
Intel Pentium 4 and some AMD Athlon computers also require a special connector known, appropriately enough, as the P4 connector. This is located on the motherboard, usually (but always) somewhere near the CPU. On computers that don't need the P4 connector, it is unused. Just tie it off out of the way of fans, other components, and metal parts.
Some other components, such as certain high-end video cards, also have a P4 connection.
Fan Power Leads
Most motherboards have a connector for the leads for the CPU fan and at least one one case fan. These provide both power and, in most cases, RPM monitoring and thermal control. If your motherboard has a header labeled CPU FAN, that's what it's for. Some motherboards also have headers for the chassis fan and/or the chipset cooler, as well.
Front Panel Leads
Every computer case comes with a set of wires that connects the motherboard to the LED's and switches on the front panel. These connectors include those for the power and reset switches, the power LED and hard drive activity LED, and the system speaker. They connect to a bus block on the motherboard.
Unfortunately, there's no standardization regarding the exact location of the panel headers. You'll just have to read the mobo manual to find the correct positions.