| UMBC CMSC 211 |
| Offset | Size | Description |
|---|---|---|
| 00h | 1 | Drive number (0=A:,1=B:,etc) |
| 01h | 1 | unit number within device driver |
| 02h | 2 | bytes per sector |
| 04h | 1 | highest sector number within cluster |
| 05h | 1 | shift count to convert clusters into sectors |
| 06h | 2 | number of reserved sectors at beginning of drive |
| 08h | 1 | number of FATs |
| 09h | 2 | number of root directory entries |
| 0Bh | 2 | number of first sector containing user data |
| 0Dh | 2 | highest cluster number (number of clusters + 1) |
| 0Fh | 2 | number of sectors per FAT |
| 11h | 2 | sector number of first directory sector |
| 13h | 2 | address of device driver header |
| 17h | 1 | media ID byte |
| 18h | 1 | 00h if disk is accessed, FF if not |
| 19h | 4 | pointer to next DPB |
| 1Dh | 2 | cluster at which to start search for free space when writing |
| 1Fh | 2 | number of free clusters on drive, FFFFh = not known |