The original trackdisk.device command set is capable of operating only up to 4GB large disks. New command set was designed by group of third party developers Ralph Babel, Randell Jesup, Oliver Kastl, Bernhard Möllemann and Ralph Schmidt.
#define TD_READ64 24 #define TD_WRITE64 25 #define TD_SEEK64 26 #define TD_FORMAT64 27
TrackDisk64 commands accept 64-bit byte offset. The lower 32 bits is passed in io_Offset and the upper 32 bits are passed in the io_Actual (io_HighOffset) field.
The maximum transfer length is still limited to 32-bits.
Testing TD64 support
To check if the underlying driver supports TD64 command set the application can send a TD_READ64 request with io_Offset, io_Actual (io_HighOffset) and io_Length all set zero. If the error IOERR_NOCMD is returned, then TrackDisk64 command set cannot be used.