Calls BIOS disk services, using INT 0x13.
#include <bios.h>
unsigned _bios_disk( unsigned service, struct _diskinfo_t *diskinfo );
| service | Disk function desired | |
| diskinfo | Disk parameters |
The _bios_disk routine uses INT 0x13 to provide several disk-access functions. The service parameter selects the function desired, while the diskinfo structure provides the necessary parameters. Note that the low-level disk operations allowed by the _bios_disk routine are very dangerous to use because they perform direct manipulation of the disk.
The diskinfo structure provides the following parameters:
| Element | Description |
| unsigned drive | Drive number |
| unsigned head | Head number |
| unsigned track | Track number |
| unsigned sector | Starting sector number |
| unsigned nsectors | Number of sectors to read, write, or compare |
| void far *buffer | Memory location to write to, read from, or compare |
The service argument can be set to one of the following manifest constants:
| Constant | Function |
| _DISK_FORMAT | Formats the track specified by diskinfo. The head and track fields indicate the track to format. Only one track can be formatted in a single call. The buffer field points to a set of sector markers. The format of the markers depends on the type of disk drive; see a technical reference to the PC BIOS to determine the marker format. The high-order byte (AH) of the return value contains the status of the call; 0 equals success. If there is an error, the high-order byte will contain a set of status flags, as defined below under Return Value. |
| _DISK_READ | Reads one or more disk sectors into memory. This service uses all fields of the structure pointed to by diskinfo, as defined earlier in this section. If no error occurs, the function returns 0 in the high-order byte and the number of sectors read in the low-order byte. If there is an error, the high-order byte (AH) will contain a set of status flags, as defined below under Return Value. |
| _DISK_RESET | Forces the disk controller to do a hard reset, preparing for floppy-disk I/O. This is useful after an error occurs in another operation, such as a read. If this service is specified, the diskinfo argument is ignored. Status is returned in the 8 high-order bits (AH) of the return value. If there is an error, the high-order byte will contain a set of status flags, as defined below under Return Value. |
| _DISK_STATUS | Obtains the status of the last disk operation. If this service is specified, the diskinfo argument is ignored. Status is returned in the 8 low-order bits (AL) of the return value. If there is an error, the low-order byte (AL) will contain a set of status flags, as defined below under Return Value. |
| _DISK_VERIFY | Checks the disk to be sure the specified sectors exist and can be read. It also runs a CRC (cyclic redundancy check) test. This service uses all fields (except buffer) of the structure pointed to by diskinfo, as defined earlier in this section. If no error occurs, the function returns 0 in the high-order byte (AH) and the number of sectors compared in the low-order byte (AL). The error status flags are listed below under Return Value. |
| _DISK_WRITE | Writes data from memory to one or more disk sectors. This service uses all fields of the structure pointed to by diskinfo, as defined earlier in this section. If no error occurs, the function returns 0 in the high-order byte (AH) and the number of sectors written in the low-order byte (AL). If there is an error, the high-order byte will contain a set of status flags, as defined below under Return Value. |
The _bios_disk function returns the value in the AX register after the BIOS interrupt.
| Bits | Meaning |
| 0x00 | No error |
| 0x01 | Invalid request or a bad command |
| 0x02 | Address mark not found |
| 0x03 | Disk write protected |
| 0x04 | Sector not found |
| 0x05 | Reset failed |
| 0x06 | Floppy disk removed |
| 0x07 | Drive parameter activity failed |
| 0x08 | Direct Memory Access (DMA) overrun |
| 0x09 | DMA crossed 64K boundary |
| 0x0A | Bad sector flag detected |
| 0x0B | Bad track flag detected |
| 0x0C | Media type not found |
| 0x0D | Invalid number of sectors on format |
| 0x0E | Control data access mark detected |
| 0x0F | DMA arbitration level out of range |
| 0x10 | Data read (CRC or ECC) error |
| 0x11 | Corrected data read (ECC) error |
| 0x20 | Controller failure |
| 0x40 | Seek error |
| 0x80 | Disk timed out or failed to respond |
| 0xAA | Drive not ready |
| 0xBB | Undefined error |
| 0xCC | Write fault on drive |
| 0xE0 | Status error |
| 0xFF | Sense operation failed |
Standards:None
16-Bit:DOS, QWIN, WIN, WIN DLL
32-Bit:None
/* BDISK.C: This program first attempts to verify a disk by using an
* invalid disk head number. After printing the return value error code,
* the program verifies the disk by using a valid disk head code.
*/
#include <conio.h>
#include <stdio.h>
#include <bios.h>
void main( void )
{
unsigned status = 0;
struct _diskinfo_t disk_info;
disk_info.drive = 0;
disk_info.head = 10; /* Invalid head number */
disk_info.track = 1;
disk_info.sector = 2;
disk_info.nsectors = 8;
printf( "Insert disk in drive A: and press any key\n" );
_getch();
status = _bios_disk( _DISK_VERIFY, &disk_info );
printf( "Return value: 0x%.4x\n", status );
if( status & 0xff00 ) /* Error if high byte is 0 */
printf( "Seek error\n" );
else
printf( "No seek error\n" );
printf( "Press any key\n" );
_getch();
disk_info.head = 0; /* Valid head number */
status = _bios_disk( _DISK_VERIFY, &disk_info );
printf( "Return value: 0x%.4x\n", status );
if( status & 0xff00 ) /* Error if high byte is 0 */
printf( "Seek error\n" );
else
printf( "No seek error\n" );
}
Insert disk in drive A: and press any key
Return value: 0x0400
Seek error
Press any key
Return value: 0x0008
No seek error