Implementing Background Utilities in MS-DOS using TSRs
Learn how to use the INT 21h/31h 'Keep Process' function to create MS-DOS TSRs, allowing background utilities to run without occupying a program slot.
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msdosHow MS-DOS TSRs Hooked Interrupts to Run Background Tasks in 640K
MS-DOS TSRs achieved background tasks by hooking interrupt vectors and staying resident via INT 21h/31h. This blog explains the mechanism, the non-reentrant kernel's InDOS flag constraint, and includes a minimal assembly example you can run in DOSBox.