MS-DOS reserves software interrupts 20h through 3Fh for its own use. Among the features these interrupts provide are the interfaces to the MS-DOS system functions and to MS-DOS programs that provide services to other programs.
Following are the MS-DOS interrupts:
| Interrupt | Description | Comments |
| 20h | Terminate Program | For use by .COM programs | |
| 21h | MS-DOS System Function | For use by all programs | |
| 22h | Termination Address | For storage only (Do not issue) | |
| 23h | CTRL+C Handler | Replaceable | |
| 24h | Critical-Error Handler | Replaceable | |
| 25h | Absolute Disk Read | ||
| 26h | Absolute Disk Write | ||
| 27h | Terminate and Stay Resident | For use by .COM programs | |
| 28h | MS-DOS Idle Handler | Extendable | |
| 29h | Fast Console | For use by MS-DOS character I/O | |
| 2Ah | Network/Critical Sections | For use by MS-DOS | |
| 2Eh | Reload Transient | For use by COMMAND.COM only | |
| 2Fh | Multiplex Interrupt | Extendable | |
| 30h | MS-DOS Entry Point | For storage only (Do not issue) | |
| 31h | MS-DOS Entry Point | For storage only (Do not issue) | |
All other reserved interrupts—2Bh through 2Dh and 32h through 3Fh—are not currently used by MS-DOS. MS-DOS assigns a default interrupt handler to each reserved interrupt it does not use. The default handler does nothing more than return to the program that issued the interrupt. default handlers>
For interrupts marked “Replaceable” or “Extendable” in the preceding table, a program can provide its own interrupt handlers to replace or enhance the existing handlers. The program should leave all other interrupts unchanged. An exception to this rule is a terminate-and-stay-resident program (TSR) that must intercept interrupts to determine when MS-DOS system functions have been called. replaceable>extendable>intercepted>