[4] IBM's 1984 introduction of the AT was seen as an unusual move for the company, which typically waited for competitors to release new products before producing its own models.

The announcement surprised rival executives, who admitted that matching IBM's prices would be difficult.

No major competitor showed a comparable computer at COMDEX Las Vegas that year.

Like the IBM PC, the AT supported an optional math co-processor chip, the Intel 80287, for faster execution of floating point operations.

[8][9] This was an improvement from the PC, which required setting the clock manually or installing an RTC expansion card.

[10] In addition to keeping the time, the RTC includes 50 bytes of CMOS memory which is used to store software-adjustable BIOS parameters.

The AT is also equipped with a physical lock that prevents access to the computer by disabling the keyboard and holding the system unit's cover in place.

The 8250 UART from the PC was upgraded to the 16450, but since both chips had single-byte buffers, high-speed serial communication was problematic as with the XT.

In normal operation this resistor drew 2.4 amperes (dissipating 28.8 watts), getting fairly hot.

The label also became a standard term in reference to PCs that used the same type of power supply, case, and motherboard layout as the 5170.

AT-class became a term describing any machine which supported the same BIOS functions, 80286 or greater processor, 16-bit expansion slots, keyboard interface, 1.2 MB 5+1⁄4 inch floppy disk drives and other defining technical features of the IBM PC AT.

In the United States, popular brands of AT clones included the Tandy 3000, Compaq Deskpro 286, HP Vectra,[26] Zenith Z-286,[27] Epson Equity Models II+[28] and III,[29] and Commodore PC-30 and PC-40.

[32] An industry analyst wrote in Computerworld in 1985 that the AT's power was evidence of IBM's belief that personal computers were more important for the company than minicomputers.

The company promised to continue manufacturing certain models of the first-generation PC, including the AT, for the coming months.