DOS
Cmd Name                     Ver. Usage Flags
                                                                     
00H Initialize device              Chr  Blk 
01H Media Check                         Blk 
02H Build BPB                           Blk 
04H Input (read from device)       Chr  Blk 
05H Non-destructive Input          Chr 
06H Input status                   Chr 
07H Input Flush                    Chr 
08H Output (write to device)       Chr  Blk 
09H Output with verify             Chr  Blk 
0aH Output Status                  Chr 
0bH Output Flush                   Chr 
0dH Device Open              3.0+  Chr  Blk       OCR 
0eH Device Close             3.0+  Chr  Blk       OCR 
0fH Removable Media          3.0+       Blk       OCR 
10H Output until busy        3.0+  Chr                      OTB 
13H Generic IOCTL Request    3.2   Chr  Blk            Gen 
17H Get Logical Device       3.2        Blk            Gen 
18H Set Logical Device       3.2        Blk            Gen 
19H IOCTL Support Query      5.0   Chr  Blk            Gen       Qry 
                                                                     

On entry to the Strategy routine (see Device Driver Basics), DOS passes
the address of a request structure in ES:BX (see DevRequestHdrRec).  The
bCmd field of that structure (at offset 2) will contain one of the above
command codes.

The variable-length data that follows the DevRequestHdrRec varies from
command to command.  Some commands share identical request structures.
Others have a unique structure and some use only the request header to
communicate with DOS.

See Also: IOCTL Functions
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Device Requests