Note: This API call is for DOS personality only. Use Family API for portability.
DOS API
Most of DOS API calls are invoked using software interrupt INT 21H. In most cases AH register are set to function number.
DOS Interrupts
| Interrupt vector | Description | Version | Notes |
|---|---|---|---|
| 20H | Terminate program | 1.0+ | Implemented in DOS kernel |
| 21H | Main DOS API | 1.0+ | Implemented in DOS kernel |
| 22H | Program terminate address | 1.0+ | Return address in calling program |
| 23H | Control-C handler address | 1.0+ | Default handler is in the command shell (usually COMMAND.COM) |
| 24H | Critical error handler address | 1.0+ | Default handler is in the command shell (usually COMMAND.COM) |
| 25H | Absolute disk read | 1.0+ | Implemented in DOS kernel, enhanced in DOS 3.31 to support up to 2 GB partitions |
| 26H | Absolute disk write | 1.0+ | Implemented in DOS kernel, enhanced in DOS 3.31 to support up to 2 GB partitions |
| 27H | Terminate and stay resident | 1.0+ | Implemented in COMMAND.COM in DOS 1.0, DOS kernel in DOS 2.0+ |
| 28H | Idle callout | 2.0+ | Called by DOS kernel when waiting for input |
| 29H | Fast console output | 2.0+ | Implemented by the builtin console device driver or a replacement driver like ANSI.SYS |
| 2AH | Networking and critical section | 3.0+ | Called by DOS kernel to interface with networking software |
| 2EH | Reload transient | 2.0+ | Implemented in COMMAND.COM |
| 2FH | Multiplex | 3.0+ | Implemented in DOS kernel and various programs (PRINT, MSCDEX, DOSKEY, APPEND, etc.) depending on subfunction number |
| DOS API | |
|---|---|
| Process manager | INT 20H, INT 21H: 00H, 25H, 26H, 31H, 34H, 35H, 4CH, INT 22H, INT 27H, INT 28H |
| File manager | INT 25H, INT 26H, INT 21H: 0DH, 0EH, 0FH, 10H, 11H, 12H, 13H, 14H, 15H, 16H, 17H, 19H, 1AH, 1BH, 1CH, 21H, 22H, 23H, 24H, 27H, 28H, 29H, 2EH, 2FH, 32H, 3305H, 36H, 39H, 3AH, 3BH |
| Character Device I/O | INT 29H, INT 21H: 01H, 02H, 03H, 04H, 05H, 06H, 07H, 08H, 09H, 0AH, 0BH, 0AH, 0CH |
| Signals | INT 23H, INT 24H, INT 21H: 3300H, 3301H, 3302H |
| Memory manager | |
| Date and Time | INT 21H: 2AH, 2BH, 2CH, 2DH |
| Misc | INT 21H: 30H, 3306H, 3700H, 3701H, 3702H, 3703H |
| NLS | INT 21H: 3303H, 3304H, 3800H, 3801H |
