The IBM PC/AT was IBM's third-generation personal computer, designed around the Intel 80286 microprocessor and released in 1984. Because the AT used various technologies that were rare at the time in personal computers, the name AT originally stood for 'advanced technology. See also IBM PC.

IBM's efforts to trademark the name AT largely failed, and numerous clones appeared. "AT" eventually became a standard term referring either to any computer utilizing a 286 processor or better, or, especially after the release of Intel's ATX specification, for motherboards whose size and screw positions approximated those of IBM's original standard power supplies that could plug into them, and cases that could house them.

The AT architecture was an ad hoc standard, and while the power supplies and motherboards that fit in one AT case usually fit another, the specifications were not universal and there were sometimes physical incompatibilities.

A so-called "AT keyboard" refers to a computer keyboard with a full-size 5-pin DIN connector compatible with the original PC/AT, as opposed to the later-style PS/2 6-pin mini-DIN connector.