IBM Personal Computer XT

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IBM PC/XT (model 5160)
Type Personal computer
Released March 8, 1983
Discontinued 1987
Processor Intel 8088 @ 4.77 MHz
Memory 128KB ~ 640KB
Operating system IBM BASIC / PC-DOS 2.0 / SCO Xenix

The IBM Personal Computer XT, often shortened to the 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 system was largely intended for business users, and a corresponding 3270 PC featuring 3270 terminal emulation was released later in October 1983. XT stands for eXtended Technology.

The standard XT originally came with 128KB of memory, a 360KB double-sided 5 1/4" full-height floppy disk drive, a 10MB Seagate ST-412 hard drive, an Asynchronous Adapter (serial card) 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 256KB of memory as standard.

There were two versions of the XT motherboard. The original could support up to 256kB on the motherboard itself (four banks of 64kB chips), with a maximum of 640kB achieved by using expansion cards. The second revision board - introduced in 1986 - could support the whole 640kB on the motherboard (two banks of 256kb chips, two banks of 64kB). The earlier boards could be adapted to 'late' specifications after a couple of minor modifications. The second revision motherboard also had a revised BIOS, which included support for the enhanced keyboard and cut booting time in half.

Late XTs came factory-fitted with half-height floppy drives, as well as the option for a 20MB hard drive and 'enhanced' keyboard (essentially a Model M without the LED panel).

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 a BASIC interpreter in ROM. Since this interpreter was meant to be used with a cassette drive (which wasn't offered on the XT), the only ways to access it were by disconnecting the hard drive and leaving the floppy drive empty, using the BASICA program (included on a floppy disk, which added extensions for using the disk drives), or invoking a BIOS call manually using a debugger.

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 use different keyboard scan codes. An XT to AT signal adapter is needed to create compatibility with modern computers. Also the 'parkbd' driver can be used under Linux in order to support either sort of keyboard via a simple adapter through the parallel port.

[edit] References

  • IBM (1983). Personal Computer Hardware Reference Library: Guide to Operations, Personal Computer XT. IBM Part Number 6936831.

[edit] See also

IBM 5160
IBM 5150     IBM 5170
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