Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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     Before a program receives control from MS-DOS, its program segment
     prefix (PSP) is set up to contain certain vital information, such
     as:
 
        ■ The segment address of the program's environment block
        ■ The command line originally entered by the user
        ■ The original contents of the terminate, CTRL+C, and critical-
          error handler vectors
        ■ The top address of available RAM
 
     The segment address of the PSP is normally passed to the program
     in registers DS and ES when it initially receives control from
     MS-DOS. This function allows a program to conveniently recover the
     PSP address at any point during its execution, without having to
     save it at program entry.
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