biosdisk_int13_extensions
err = biosdisk_int13_extensions (0x4B01, drive, &cdrp);
err = biosdisk_int13_extensions (0x4800, drive, &drp);
extern int biosdisk_int13_extensions (int ax, int drive, void *dap);
err = biosdisk_int13_extensions ((read + 0x42) << 8, drive, &dap);