A Macintosh (or a Mac for short) is a computer system that has Mac OS for its OS. There are a few different companies that have produced Macs, but by far the largest is Apple. The oldest Macs are based on the 68xx processor; somewhat more recent Macs on the PowerPC processor, and current Macs on the x86 processor. The Macintosh was really the first general purpose computer to employ a GUI.