XT bus architecture

The XT bus architecture is an eight-bit ISA bus architecture used by Intel 8086 and Intel 8088 systems in the IBM PC and IBM PC XT in the 1980s. It predates the 16-bit ISA architecture used on IBM PC AT machines.

The XT bus has four DMA channels, of which three are brought out to the expansion slots. Of these three, two are normally allocated to machine functions:

DMA channel	Expansion	Standard function
0	No	dynamic RAM refresh
1	Yes	add-on cards
2	Yes	floppy disk controller
3	Yes	hard disk controller

See also

• Extended Industry Standard Architecture (EISA)
• Micro Channel Architecture (MCA)
• Peripheral Component Interconnect (PCI)

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.