MS-DOS_API

DOS API

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The DOS API is an API which originated with 86-DOS and is used in MS-DOS/PC DOS and other DOS-compatible operating systems. Most calls to the DOS API are invoked using software interrupt 21h (INT 21h). By calling INT 21h with a subfunction number in the AH processor register and other parameters in other registers, various DOS services can be invoked. These include handling keyboard input, video output, disk file access, program execution, memory allocation, and various other activities. In the late 1980s, DOS extenders along with the DOS Protected Mode Interface (DPMI) allow the programs to run in either 16-bit or 32-bit protected mode and still have access to the DOS API.

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This article uses material from the Wikipedia article MS-DOS_API, and is written by contributors. Text is available under a CC BY-SA 4.0 International License; additional terms may apply. Images, videos and audio are available under their respective licenses.

[1] [1]
Ray Duncan (1988). Advanced MS-DOS Programming: The Microsoft Guide for Assembly Language and C Programmers. Microsoft Press. ISBN 0914845772.

[1]

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 built-in 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
`2Bh`	Unused
`2Ch`	Unused
`2Dh`	Unused
`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

`AH`	Description	Version
`00h`	Program terminate	1.0+
`01h`	Character input	1.0+
`02h`	Character output	1.0+
`03h`	Auxiliary input	1.0+
`04h`	Auxiliary output	1.0+
`05h`	Printer output	1.0+
`06h`	Direct console I/O	1.0+
`07h`	Direct console input without echo	1.0+
`08h`	Console input without echo	1.0+
`09h`	Display string	1.0+
`0Ah`	Buffered keyboard input	1.0+
`0Bh`	Get input status	1.0+
`0Ch`	Flush input buffer and input	1.0+
`0Dh`	Disk reset	1.0+
`0Eh`	Set default drive	1.0+
`0Fh`	Open file	1.0+
`10h`	Close file	1.0+
`11h`	Find first file	1.0+
`12h`	Find next file	1.0+
`13h`	Delete file	1.0+
`14h`	Sequential read	1.0+
`15h`	Sequential write	1.0+
`16h`	Create or truncate file	1.0+
`17h`	Rename file	1.0+
`18h`	Reserved	1.0+
`19h`	Get default drive	1.0+
`1Ah`	Set disk transfer address	1.0+
`1Bh`	Get allocation info for default drive	1.0+
`1Ch`	Get allocation info for specified drive	1.0+
`1Dh`	Reserved	1.0+
`1Eh`	Reserved	1.0+
`1Fh`	Get disk parameter block for default drive	1.0+
`20h`	Reserved	1.0+
`21h`	Random read	1.0+
`22h`	Random write	1.0+
`23h`	Get file size in records	1.0+
`24h`	Set random record number	1.0+
`25h`	Set interrupt vector	1.0+
`26h`	Create PSP	1.0+
`27h`	Random block read	1.0+
`28h`	Random block write	1.0+
`29h`	Parse filename	1.0+
`2Ah`	Get date	1.0+
`2Bh`	Set date	1.0+
`2Ch`	Get time	1.0+
`2Dh`	Set time	1.0+
`2Eh`	Set verify flag	1.0+
`2Fh`	Get disk transfer address	2.0+
`30h`	Get DOS version	2.0+
`31h`	Terminate and stay resident	2.0+
`32h`	Get disk parameter block for specified drive	2.0+
`33h`	Get or set Ctrl-Break	2.0+
`34h`	Get InDOS flag pointer	2.0+
`35h`	Get interrupt vector	2.0+
`36h`	Get free disk space	2.0+
`37h`	Get or set switch character	2.0+
`38h`	Get or set country info	2.0+
`39h`	Create subdirectory	2.0+
`3Ah`	Remove subdirectory	2.0+
`3Bh`	Change current directory	2.0+
`3Ch`	Create or truncate file	2.0+
`3Dh`	Open file	2.0+
`3Eh`	Close file	2.0+
`3Fh`	Read file or device	2.0+
`40h`	Write file or device	2.0+
`41h`	Delete file	2.0+
`42h`	Move file pointer	2.0+
`43h`	Get or set file attributes	2.0+
`44h`	I/O control for devices	2.0+
`45h`	Duplicate handle	2.0+
`46h`	Redirect handle	2.0+
`47h`	Get current directory	2.0+
`48h`	Allocate memory	2.0+
`49h`	Release memory	2.0+
`4Ah`	Reallocate memory	2.0+
`4Bh`	Execute program	2.0+
`4Ch`	Terminate with return code	2.0+
`4Dh`	Get program return code	2.0+
`4Eh`	Find first file	2.0+
`4Fh`	Find next file	2.0+
`50h`	Set current PSP	2.0+
`51h`	Get current PSP	2.0+
`52h`	Get DOS internal pointers (SYSVARS)	2.0+
`53h`	Create disk parameter block	2.0+
`54h`	Get verify flag	2.0+
`55h`	Create program PSP	2.0+
`56h`	Rename file	2.0+
`57h`	Get or set file date and time	2.0+
`58h`	Get or set allocation strategy	2.11+
`59h`	Get extended error info	3.0+
`5Ah`	Create unique file	3.0+
`5Bh`	Create new file	3.0+
`5Ch`	Lock or unlock file	3.0+
`5Dh`	File sharing functions	3.0+
`5Eh`	Network functions	3.0+
`5Fh`	Network redirection functions	3.0+
`60h`	Qualify filename	3.0+
`61h`	Reserved	3.0+
`62h`	Get current PSP	3.0+
`63h`	Get DBCS lead byte table pointer	3.0+
`64h`	Set wait for external event flag	3.2+
`65h`	Get extended country info	3.3+
`66h`	Get or set code page	3.3+
`67h`	Set handle count	3.3+
`68h`	Commit file	3.3+
`69h`	Get or set media id	4.0+
`6Ah`	Commit file	4.0+
`6Bh`	Reserved	4.0+
`6Ch`	Extended open/create file	4.0+

MS-DOS_API

DOS API

History of the DOS API

The DOS API and Windows

Interrupt vectors used by DOS

DOS INT 21h services

Operating systems with native support

Operating systems with DOS emulation layer

Other emulators

See also

References

Further reading

External links

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