INT 2F U - DOS 3.2+ - SET DISK INTERRUPT HANDLER
AH = 13h
DS:DX -> interrupt handler disk driver calls on read/write
ES:BX = address to restore INT 13 to on system halt (exit from root
shell) or warm boot (INT 19)
Return: DS:DX from previous invocation of this function
ES:BX from previous invocation of this function
Notes:  IO.SYS hooks INT 13 and inserts one or more filters ahead of the
original INT 13 handler.  The first is for disk change detection
on floppy drives, the second is for tracking formatting calls and
correcting DMA boundary errors, the third is for working around
problems in a particular version of IBM's ROM BIOS
before the first call, ES:BX points at the original BIOS INT 13; DS:DX
also points there unless IO.SYS has installed a special filter for
hard disk reads (on systems with model byte FCh and BIOS date
"01/10/84" only), in which case it points at the special filter
most DOS 3.3+ disk access is via the vector in DS:DX, although a few
functions are still invoked via an INT 13 instruction
this is a dangerous security loophole for any virus-monitoring software
which does not trap this call (many Bulgarian viruses are known to
use it to get the original ROM entry point)
SeeAlso: INT 19

See also: 1301

2F13 - DOS 3.2+ - SET DISK INTERRUPT HANDLER