Table 1.  Stack Contents on Entry to Critical Error Handler

   SP Offset

     +00h      IP        DOS return address and flags
     +02h      CS         an IRET from here will go to DOS
     +04h      flags
     
     +06h      AX        your applications registers
     +08h      BX
     +0ah      CX
     +0ch      DX
     +0eh      SI
     +10h      DI
     +12h      BP
     +14h      DS
     +16h      ES
     
     +18h      IP        your application return address
     +1ah      CS
     +1ch      flags


Table 2.  Error Codes in DI

     0    Write-protected disk
     1    Unknown unit (invalid drive number)
     2    Drive not ready (door open or no disk)
     3    Unknown command (request not supported by device driver)
     4    CRC error
     5    Bad request structure length
     6    Seek error (could not access requested track)
     7    Unknown media (unrecognized disk format)
     8    Sector not found
     9    Printer out of paper
     10   Device write error
     11   Device read error
     12   General error


Table 3.  Disk Error Operation and Area Data in AH

     AH Bits

     2   1   0
     x   x   0      Read Operation
     x   x   1      Write Operation
     0   0   x      Error occurred in DOS system file area
     0   1   x      Error occurred in FAT area
     1   0   x      Error occurred in Directory area
     1   1   x      Error occurred in Data area
