IBM Personal Computer AT

The IBM Personal Computer AT, more commonly known as the IBM AT and also sometimes called the PC AT or PC/AT, was IBM's second-generation PC, designed around the 6 MHz Intel 80286 microprocessor and released in 1984 as System Unit 5170. The name AT stood for "Advanced Technology", and was chosen because the AT offered various technologies that were then new in personal computers; one such advancement was that the 80286 processor supported protected mode. IBM later released an 8 MHz version of the AT.