Will a TSR DOS program work ok under windows? How to make a simple TSR program?
Thanks.

Generally, they should work just fine, just that they will only be resident for one command shell. On 9x, some TSRs can be loaded before windows start and will thus be resident for all dos boxes opened, but there's a bunch of restrictions. Some TSRs will cause 9x to run certain things in compatibility mode, which means BIOS access instead of native 32bit drivers - this is _slow_. NT doesn't have any dos code, so this doesn't apply here.

An example of a TSR that works okay would be http://www.autofish.net/zzt/files/rat.zip , a resident ascii table - I used this a lot in the dos days. It's a bit funny actually - if you launch cmd.exe from 2k or XP, it will be pretty fast even in windowed mode. But if you run RAT, it seems it causes the console to run in compatibility mode, like if you launch edit.com, and the console will be painfully slow when windowed. Fullscreen should still work pretty okay, though.

I don't have any TSR code at hand, sorry - I stopped messing around with dos a lot of years ago , but this has been done quite a lot, so I guess a google search for "dos assembly/asm tsr" or the like should turn up some results - probably not anything/a lot in fasm, though.

also don't forget that windoze timer is extremelly inaccurate for DOS programs (if you tried to play DOS game under windoze you know it ). That means all time-critical code (including sound output) will act wrong, so better forget about hooking ints 08 or 1C.

You also can't setup hardware (PIC, PIT, VGA ...).