Most calls to the DOS API are invoked using software interrupt 21h (INT 21h).
These include handling keyboard input, video output, disk file access, program execution, memory allocation, and various other activities.
In MS-DOS 3.31, the INT 25h/26h functions were enhanced to support hard disks greater than 32 MB.
The following is the list of interrupt vectors used by programs to invoke the DOS API functions.
The following is the list of functions provided via the DOS API primary software interrupt vector.