XT bus architecture

(After the IBM PC XT) 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 the Intel 80286 based 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 disc} controller