for us in the 1980s we had dos 4 on a shelf and stuck with dos 3.3.

we sold accounting software and it took a lot of conventional memory. 484k or so iirc. when you used dos 4.

* we loaded a keyboard driver for uk/irish keyboards. otherwise we'd have no £ for documents.

* share.exe for file locking

* ipx for novell networking

* driver for network card.

on dos 4 that usually left us about 4k short to run the accounting software. we had to wait till dos 5 came to move past dos 3.3