This command is structured as a standard OS/2 request packet. Note that the fields prefixed by DD_ are filled in by the physical device driver. (See the following table.) 

┌──────────────────────────────┬──────────────────────────────┐
│Field                         │Length                        │
├──────────────────────────────┼──────────────────────────────┤
│Request Header                │13 BYTES                      │
├──────────────────────────────┼──────────────────────────────┤
│Reserved.  Must be zero.      │3 BYTES                       │
├──────────────────────────────┼──────────────────────────────┤
│DD_CapStruct                  │DWORD                         │
├──────────────────────────────┼──────────────────────────────┤
│DD_VolCharStruct              │DWORD                         │
└──────────────────────────────┴──────────────────────────────┘