struc ReadWriteRequest          ; Device-Driver functions 04h, 08h, 09h
 rwrLength      db ?            ; Length of structure, in bytes
 rwrUnit        db ?            ; Unit number (block device only)
 rwrFunction    db ?            ; Function number (04h, 08h, or 09h)
 rwrStatus      dw ?            ; Status
 rwrReserved    db 8 dup (?)    ; Reserved
 rwrMediaID     db ?            ; INPUT:  media descriptor
 rwrBuffer      dd ?            ; INPUT:  buffer address
 rwrBytesSec    dw ?            ; INPUT:  no. of bytes/sectors to r/w
                                ; OUTPUT: no. of bytes/sectors r/w
 rwrStartSec    dw ?            ; INPUT:  starting sector number
 rwrVolumeID    dd ?            ; OUTPUT: volume identifier
 rwrHugeStartSec dd ?           ; INPUT:  32-bit starting-sector number
ends                            ; = 30d bytes