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The AT keyboard was used in IBM® and competitor PCs in the 1980s, with 84 keys arranged in three groups. It had a 5-pin round connector and bi-directional electrical signaling. The AT keyboard was replaced by the 101-key Enhanced Keyboard, which became an industry standard.
The AT keyboard, named for the AT series of Personal Computers (PCs) with which it was included, was a type of computer keyboard used by IBM® and its competitors in the 1980s. It had 84 keys arranged in three distinct groups, with letters and commonly used keys such as the spacebar occupying the center, a set of function keys to the left, and a number pad to the right. The AT keyboard used a 5-pin round connector and electrical signaling scheme that survived on the keyboards themselves. Today, these types of keyboards are typically only used in older hardware configurations and historic displays.
PC keyboards can be divided into three distinct generations based on the layout of the keys. Early keyboards included with early IBM® PC models had awkward key locations and little or no separation between different key types. Also, important keys like Shift and Enter were small and labeled only with symbols. IBM® solved many of these problems with the AT keyboard, named for the AT series of PCs it was originally included with.
Unlike its predecessor, the AT keyboard had three distinct sets of keys. To the left were ten function keys, to the right was a numeric keypad, and in the center were commonly used keys, including Shift, Enter, and the space bar. The general layout of the AT keyboard is quite similar to most modern computer keyboards, with a few notable exceptions. Beneath the TAB key was a Ctrl key, with the Caps Lock key positioned in the lower right under the Shift key. The Esc key was located on the right with the numeric keypad. There were no dedicated arrow keys; the two, four, six, and eight keys on the numeric keypad double as the down, left, up, and right arrow keys.
In addition to refining the keyboard layout, IBM® made changes to both the physical connector and electrical signaling used in the AT keyboard. The physical connector was a round plug about half an inch (1.27 cm) in diameter, with five metal pins and a small indentation to prevent the connector from being plugged in upside down. Electrical signaling was bi-directional, meaning a PC could send data to the keyboard just as the keyboard sent data to the PC.
Just a few years after the debut of the AT keyboard, IBM® released a new “Enhanced Keyboard” with 101 keys. This keyboard layout became an industry standard, supplanting previous layouts and remaining mostly unchanged for over twenty years. Some aspects of the AT keyboard carried over to the new design, including the 5-pin connector and signaling protocol, which was used until the introduction of Universal Serial Bus (USB) keyboards.
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