The '''MS-DOS API''' is an [[API]] used originally in [[MS-DOS]]/[[PC-DOS]], and later by other operating[[DOS]] systems compatible with MS-DOS. The DOS API is based on [[software interrupt]] 21h (int 21h). By calling int 21h with the subfunction in AH and the other parameters in other registers, one invokes various DOS services. DOS services include keyboard input, video output, disk file access, executing programs, memory allocation, and various other things. There are various implementations of the DOS API, including MS-DOS, PC-DOS, DR-DOS, FreeDOS, PTS-DOS, and others. The DOS API is based on the [[BIOS]], and [[DOS]] routines often internally access [[BIOS interrupt call]]s.
The [[DOS Protected Mode Interface]] extends the DOS API to 32-bits.
