was useful only for sounding beep codes on older terminal systems. The most common P/Ns with speakers are 1394540 and 51G872, made for RS/6000 UNIX workstations. Model Ms have been manufactured to quite a number of different interface and connector standards, some of which (such as the 5-pin DIN used on 5250 terminals) are poorly documented and have had to be reverse-engineered by enthusiasts. Early variants shipped with the PC XT and AT used connectors specific to those systems. After the introduction of the PS/2 most shipped with a connector for a PS/2 port; these included the 1391401. Unicomp introduced support for USB. Older model Ms used a detachable cable with an SDL connector on the keyboard, later Lexmark and Unicomp variants used a fixed cable, and one very recent variant from Unicomp has a detachable cable with an uncommon locking variant of the USB Type A jack on the keyboard. Features by part number Layout types: 101 – ANSI layout, the model M's original. 102 – International layout with additional key between Z and a half-sized left shift, AltGr in place of right Alt, usually with ISO-style long Enter. 103 – ANSI layout with one Super key and one Menu key, long spacebar. 104 – ANSI layout plus two Windows keys and one Menu key, short spacebar. 122 – IBM terminal layout with extra function keys and left-side function pad. 84 – Tenkeyless version of the 101-key ANSI layout. 87 – Tenkeyless version of the 104-key ANSI layout. Logo position legend: LC – Left Corner RC – Right Corner LLC – Lower Left Corner LRC – Lower Right Corner ULC – Upper Left Corner URC – Upper Right Corner LLP – Lock-Light Panel Click [show] to display the table's contents. Note: Manufacture dates are approximate. Gallery See also IBM PC keyboard Model F keyboard List of mechanical keyboards References External links – another guide to Model M history and variants – Interoperability problems with modern hardware. – current Model M manufacturer – a Model M restoration guide – Comprehensive review Computer keyboard models IBM personal computers