Original PC Hardware Reference

CD: 20 Original PC Hardware Reference
All XT models include a heavy-duty, fan-cooled, 130-watt power supply to support the greater
expansion capabilities and disk drive options. The power supply has more than double the capacity
of the PC’s supply and can easily support hard disk drives and the full complement of expansion
cards.
An 83-key keyboard was standard equipment with the early XT models but was changed to an
enhanced 101-key unit in the more recent models. The keyboard is attached to the system unit
by a six-foot coiled cable.
All models of the PC XT system unit contain these major functional components:
■ Intel 8088 microprocessor
■ ROM-based diagnostics (POST)
■ BASIC language interpreter in ROM
■ 256KB or 640KB of Dynamic RAM
■ Floppy disk controller
■ One 360KB floppy drive (full- or half-height)
■ 10MB or 20MB hard disk drive with interface (enhanced models)
■ Serial interface (enhanced models)
■ Heavy-duty, 135-watt power supply
■ Eight I/O expansion slots
■ Socket for 8087 math coprocessor
XT Models and Features
The XT was available in many different model configurations, but originally only one model was
available. This original model included a 10MB hard disk, marking the first time that a hard disk
was standard equipment in a personal computer, and was properly supported by the operating
system and peripherals. This computer helped change the industry standard for PCs from normally
having only one or two floppy disk drives to now including one or more hard disks.
Today, most people wouldn’t consider a PC to be even remotely usable without a hard disk. The
original XT was expensive, however, and buyers couldn’t unbundle, or delete, the hard disk from
the system at purchase time for credit, and then add it later. This fact distinguished the XT from
the PC and misled many people to believe that the only difference between the two computers
was the hard disk. People who recognized and wanted the greater capabilities of the XT without
the standard IBM hard disk, unfortunately, had to wait for IBM to sell versions of the XT without
the hard disk drive.
The original Model 087 of the XT included a 10MB hard disk, 128KB of RAM, and a standard
serial interface. IBM later increased the standard memory in all PC systems to 256KB. The XT
reflected the change in Model 086, which was the same as the preceding 087 except for a standard
256KB of RAM.