Offset Size Description
00 byte length in bytes of the request header
01 byte unit code; the sub-unit the operation is for (block
devices); meaningless for character devices
02 word command code, (see DEVICE COMMANDS)
04 8bytes reserved for DOS
0C nbytes request data (variable length)
- see INT 21,44 or DEVICE ATTRIBUTES or DEVICE CODES
- see also IOCTL,n where "n" is an IOCTL function