8-bit ISA (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 Nodynamic RAM refresh
1 add-on cards
2 floppy disk controller
3 hard disk controller