| 1 | A | B | C | D |
| --- | --- | --- | --- | --- |
| 2 | DOS API - Interrupt vectors used by DOS |  |  |  |
| 3 | Interrupt vector | Description | Version | Notes |
| 4 | 20h | Terminate program | 1.0+ | Implemented in DOS kernel |
| 5 | 21h | Main DOS API | 1.0+ | Implemented in DOS kernel |
| 6 | 22h | Program terminate address | 1.0+ | Return address in calling program |
| 7 | 23h | Control-C handler address | 1.0+ | Default handler is in the command shell (usually COMMAND.COM) |
| 8 | 24h | Critical error handler address | 1.0+ | Default handler is in the command shell (usually COMMAND.COM) |
| 9 | 25h | Absolute disk read | 1.0+ | Implemented in DOS kernel, enhanced in DOS 3.31 to support up to 2 GB partitions |
| 10 | 26h | Absolute disk write | 1.0+ | Implemented in DOS kernel, enhanced in DOS 3.31 to support up to 2 GB partitions |
| 11 | 27h | Terminate and stay resident | 1.0+ | Implemented in COMMAND.COM in DOS 1.0, DOS kernel in DOS 2.0+ |
| 12 | 28h | Idle callout | 2.0+ | Called by DOS kernel when waiting for input |
| 13 | 29h | Fast console output | 2.0+ | Implemented by the builtin console device driver or a replacement driver like ANSI.SYS |
| 14 | 2Ah | Networking and critical section | 3.0+ | Called by DOS kernel to interface with networking software |
| 15 | 2Bh | Unused | - | - |
| 16 | 2Ch | Unused | - | - |
| 17 | 2Dh | Unused | - | - |
| 18 | 2Eh | Reload transient | 2.0+ | Implemented in COMMAND.COM |
| 19 | 2Fh | Multiplex | 3.0+ | Implemented in DOS kernel and various programs (PRINT, MSCDEX, DOSKEY, APPEND, etc.) depending on subfunction number |

Question: What is enhanced in DOS 3.31?
Answer: In DOS 3.31, the INT 25h/26h functions are enhanced.