19H query DOS default disk           0eH select DOS default disk
47H query current default directory  3bH set default directory
2fH query DTA (Disk Transfer Addr)   1aH set DTA
54H query disk verify status         2eH set disk verify status

36H get total and free disk space
32H get DPB disk info                1bH 1cH get disk info  superseded 

3305H query ID of boot drive

0dH reset disk (flush buffers)       DS IOCTL 'F' flush DoubleSpace cache
DS IOCTL 'I' invalidate Dblspace cache
INT 13H BIOS Disk services
INT 24H critical error handler address
INT 25H/26H DOS direct disk read/write

DoubleSpace API (see if disk is compressed, swap IDs, real free space,etc.)

                                              Block device IOCTL functions  
440dH 60H get device parameters      440dH 40H set device parameters
440dH 61H read track                 440dH 41H write track
440dH 62H verify track               440dH 42H format and verify track
440dH 66H query media ID             440dH 46H set media ID
440dH 68H sense media type

4408H removable media query
440eH get logical drive              440fH set logical drive
4411H query IOCTL device
                                                                              

Disk Drive Functions