Note: This API call is for DOS personality only. Use Family API for portability.

2018/09/07 07:04 · prokushev

Int 21H, AH=31H


2 and higher



Family API


      AH = 31h
      AL = return code
      DX = number of paragraphs to keep resident


never returns


the value in DX only affects the memory block containing the PSP;
        additional memory allocated via AH=48h is not affected
      the minimum number of paragraphs which will remain resident is 11h
        for DOS 2.x and 06h for DOS 3.0+
      most TSRs can save some memory by releasing their environment block
        before terminating (see #01378 at AH=26h,AH=49h)
      any open files remain open, so one should close any files which will
        not be used before going resident; to access a file which is left
        open from the TSR, one must switch PSP segments first (see AH=50h)

See also

AH=00h,AH=4Ch,AH=4Dh,INT 20,INT 22,INT 27


Process manager INT 20H, INT 21H: 00H, 25H, 26H, 31H, 34H, 35H, 4CH, INT 22H, INT 27H, INT 28H
File manager INT 25H, INT 26H, INT 21H: 0DH, 0EH, 0FH, 10H, 11H, 12H, 13H, 14H, 15H, 16H, 17H, 19H, 1AH, 1BH, 1CH, 21H, 22H, 23H, 24H, 27H, 28H, 29H, 2EH, 2FH, 32H, 3305H, 36H, 39H, 3AH, 3BH
Character Device I/O INT 29H, INT 21H: 01H, 02H, 03H, 04H, 05H, 06H, 07H, 08H, 09H, 0AH, 0BH, 0AH, 0CH
Signals INT 23H, INT 24H, INT 21H: 3300H, 3301H, 3302H
Memory manager
Date and Time INT 21H: 2AH, 2BH, 2CH, 2DH
Misc INT 21H: 30H, 3306H, 3700H, 3701H, 3702H, 3703H
NLS INT 21H: 3303H, 3304H, 3800H, 3801H
2018/09/04 19:23 · prokushev

en/docs/dos/api/int21/31.txt · Last modified: 2020/12/09 05:27 by prokushev