It usually comes with a power transformer and wires to provide power to the various parts. Sometimes called the form factor, most boxes are either ATI or the larger ATX sizes. The central processing unit is where programs go through mathematical functions to do their work. The motherboard has a place to install the CPU, RAM and wires leading to the hard drive, floppy drive, CD-ROM drivers and others.
Cards plug into the motherboard.
The performance of video cards vary greatly. Office computers can get by on simple cards with as little as 4 megabytes of memory, but improved video and a good monitor can ease eyestrain. A card that translates data from the computer into signals that can be sent over telephone lines. Some computers can get by without a sound card, relying on a tiny speaker provided with the box that only beeps. Gamers, of course, want cards that offer multiple channels capable of re-creating the sounds of World Wide Conflict.