Editing IBM Personal Computer AT (section)

=== Peripherals ===
The AT included the [[AT keyboard]], initially a new 84-key layout (the 84th key being [[System request|SysRq]]). The numerical keypad was now clearly separated from the main key group, and indicator [[light-emitting diode|LEDs]] were added for Caps Lock, Scroll Lock and Num Lock. The AT keyboard uses the same 5-pin [[DIN connector]] as the PC keyboard, but a different, bidirectional electrical interface with different keyboard [[scan code]]s. The bidirectional interface allows the computer to set the LED indicators on the keyboard, reset the keyboard, set the typematic rate, and other features. Later ATs included 101-key keyboards, e.g. the [[Model M keyboard]].

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

ATs could be equipped with [[Color Graphics Adapter|CGA]], [[IBM Monochrome Display Adapter|MDA]], [[Enhanced Graphics Adapter|EGA]], or [[Professional Graphics Controller|PGA]] video cards.

The [[8250 UART]] from the PC was upgraded to the [[Universal asynchronous receiver/transmitter#UART models|16450]], but since both chips had single-byte buffers, high-speed serial communication was problematic as with the XT.<ref name="NickallsRamasubramanian1995">{{cite book|first1=Richard W. D. |last1=Nickalls |first2=R. |last2=Ramasubramanian |title=Interfacing the IBM-PC to Medical Equipment: The Art of Serial Communication |url=https://archive.org/details/interfacingibmpc0000nick |url-access=registration |year=1995 |publisher=Cambridge University Press |isbn=978-0-521-46280-8|page=[https://archive.org/details/interfacingibmpc0000nick/page/25 25]}}</ref>