The DOS functions are a haphazard set of file, device, memory, and process

control services that are available to any program which is capable of

setting registers and invoking software interrupts.

To access DOS functions:

  Place a DOS Function Number in the AH register (if one or more

sub-functions exist, its value usually goes in AL)

  Load up the other registers as described in the function summary

  Prepare any buffers, ASCIIZ strings, and control blocks needed

  Be aware of (or set) the location of the DTA if necessary

  Invoke INT 21H

  Look for error indicators returned by DOS (examine the Carry Flag)

DOS preserves the entry values of all registers except when information is

returned in a register.

As DOS evolved, later version have remained mostly compatible with earlier

versions.  See DOS Versions for a discussion of incompatibilities.

See Also: DOS Functions

DOS Interrupts

DOS Fns by Category

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