The IBM 3270 PC (IBM System Unit 5271), released in October 1983, was an IBM PC XT containing additional hardware which could emulate the behaviour of an IBM 3270 terminal. It could therefore be used both as a standalone computer, and as a terminal to a mainframe.IBM later released the 3270 AT (IBM System Unit 5273), which was a similar design based on the IBM PC AT. They also released high-end graphics versions of the 3270 PC in both XT and AT variants.