MS-DOS version 2.0 and later versions have introduced functions that supersede many of the functions introduced in earlier versions. The newer functions are more efficient and easier to use. A programmer should not use a superseded function except to maintain compatibility with versions of MS-DOS earlier than version 2.0.
The following table shows the number and name of each superseded Interrupt 21h function and of any functions that supersede it:
| Old function | New function |
| 00h Terminate Program | 4Ch End Program |
| 01h Read Keyboard with Echo | 3Fh Read File or Device |
| 02h Display Character | 40h Write File or Device |
| 03h Auxiliary Input | 3Fh Read File or Device |
| 04h Auxiliary Output | 40h Write File or Device |
| 05h Print Character | 40h Write File or Device |
| 09h Display String | 40h Write File or Device |
| 0Ah Buffered Keyboard Input | 3Fh Read File or Device |
| 0Fh Open File with FCB | 3Dh Open File with Handle |
| 10h Close File with FCB | 3Eh Close File with Handle |
| 11h Find First File with FCB | 4Eh Find First File |
| 12h Find Next File with FCB | 4Fh Find Next File |
| 13h Delete File with FCB | 41h Delete File |
| 14h Sequential Read | 3Fh Read File or Device |
| 15h Sequential Write | 40h Write File or Device |
| 16h Create File with FCB | 3Ch Create File with Handle |
| 17h Rename File with FCB | 56h Rename File |
| 1Bh Get Default Drive Data | 36h Get Disk Free Space |
| 1Ch Get Drive Data | 36h Get Disk Free Space |
| 21h Random Read | 3Fh Read File or Device |
| 22h Random Write | 40h Write File or Device |
| 23h Get File Size | 42h Move File Pointer |
| 24h Set Random Record Number | 42h Move File Pointer |
| 26h Create New PSP | 4B00h Load and Execute Program |
| 27h Random Block Read | 3Fh Read File or Device |
| 42h Move File Pointer | |
| 28h Random Block Write | 40h Write File or Device |
| 42h Move File Pointer |
Some programmers may work on older software that still uses superseded functions. For the convenience of these programmers, this chapter includes reference pages for the superseded functions. New programs should not use superseded functions, because Microsoft may remove support for these functions at any time.