The Free On-line Dictionary of Computing (30 December 2018):

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

   (1997-09-15)