I remember in the naughts, coming across a dos machine that was quite out of time… even for the university basement it was living in next to a pile of lead brick. Its only job was to run an instrument via an home-built ISA card and write data out to 5.25” floppies.
What uses would this code have in 2026?
It was a different era entirely; Writing a TSR was a right of passage. Sometimes just getting something to work without having any other motive was enough to do it.
A clever and small TSR might keep a copy of itself in memory and not require two floppies in the case of no hard drive. In comparison to today’s standards, it’s amazing what we did with 640k (or less!) of ram.
About the worst mal-ware it can have is a boot sector that installs a "terminate, stay resident" (TSR) that copies itself onto any floppy that gets inserted.