IBM Personal Computer XT
|Release date||March 8, 1983|
|Operating system||IBM BASIC / PC-DOS 2.0-3.20 / SCO Xenix|
|CPU||Intel 8088 @ 4.77 MHz|
|Memory||128KB ~ 640KB|
The IBM Personal Computer XT, often shortened to the IBM XT, PC XT, or simply XT, was IBM's successor to the original IBM PC. It was released as IBM product number 5160 on March 8, 1983, and came standard with a hard drive. It was based on essentially the same architecture as the original PC, with only incremental improvements; a new 16-bit bus architecture would follow in the AT. The XT was mainly intended as an enhanced machine for business use, and a corresponding 3270 PC featuring 3270 terminal emulation was released later in October 1983. XT stands for X-tended Technology.
The standard XT originally came with 128KB of memory, a 360KB double-sided 5.25" full-height floppy disk drive, a 10MB Seagate ST-412 hard drive with Xebec 1210 MFM controller, an Asynchronous Adapter (serial card with 8250 UART) and a 130W PSU. The motherboard had eight 8-bit ISA expansion slots, and an Intel 8088 microprocessor running at 4.77 MHz (with a socket for an 8087 math coprocessor); the operating system usually sold with it was PC-DOS 2.0 and above. The eight expansion slots were an increase over the five in the IBM PC, although three were taken up by the floppy drive adapter, the hard drive adapter, and the Async card. The basic specification was soon upgraded to have 256k of memory as standard. Slot 8 on the XT motherboard was wired slightly different than the other slots, making it incompatible with some cards. This was done for cards designed to allow the XT to be connected to IBM mainframes. Video cards initially comprised the MDA and CGA, with EGA and PGC becoming available in 1984.
There were two configurations of the XT motherboard. The first could support up to 256k on the motherboard itself (four banks of 64kB chips), with a maximum of 640k achieved by using expansion cards. This was the configuration the XT originally shipped in. The second configuration - introduced in stock units in 1986 - could support the whole 640k on the motherboard (two banks of 256kb chips, two banks of 64kB), had the later revision AT-compatible BIOS with a faster booting time, as well as support for 101-key keyboards and 3.5" floppy drives. The earlier configuration could be adapted to 'late' configuration after a couple of minor modifications.
There were also two revisions of the motherboard, however there are only minor differences between them. Most notable is that the first revision is missing U90 and has some parts located at another place on the motherboard.
Beginning in 1985, the XT was offered in floppy-only models without a hard disk. XTs with the 256k-640k motherboard came standard with half-height floppy drives in place of the full-height drives, as well as the option for a 20MB half-height hard disk and 'enhanced' keyboard (essentially a Model M without the LED panel and a 5-pin AT-style connector). The XT was discontinued in the spring of 1987, replaced by the PS/2 Model 30.
In 1986, the XT/286 (IBM 5162) with a 6 MHz Intel 80286 processor was introduced. This system actually turned out to be faster than the ATs of the time using 8 MHz 286 processors due to the fact that it had zero wait state RAM that could move data more quickly.
Like the original PC, the XT came with BASIC in its ROM. Despite the lack of a cassette port on XTs, IBM's licensing agreement with Microsoft forced them to include BASIC on all their machines.
PC and XT keyboards are not compatible with those on more modern PCs (IBM AT or newer) even with DIN to PS/2 mini-DIN plug adapters, because PC/XT keyboards have a different transfer protocol from PC/AT keyboards and also use different keyboard scan codes. Some keyboards are switchable between the two interfaces for compatibility with either computer. Also, the 'parkbd' driver can be used under Linux in order to support either sort of keyboard through the parallel port via a simple adapter.