tag

#interrupts

2 posts

FreeDOSDeep Dive March 27, 2026 4 min read

Understanding Interrupts on FreeDOS: INT 21h and the DOS API

How DOS exposes its entire system call interface through the software interrupt mechanism, with INT 21h as the single most important entry point.

#interrupts#dos-api#freedos

FreeDOSDeep Dive February 3, 2026 4 min read

TSR Programs: How DOS Ran Background Tasks Without Multitasking

DOS had no scheduler and no processes in the modern sense — so how did pop-up utilities, mouse drivers, and print spoolers run 'in the background'? By staying resident and hooking interrupts.

#tsr#freedos#dos