I could get the extra 48KB memory for less than IBM charged. More importantly, double sided floppy drives were already on the market but you couldn't get them from IBM at any price.

So I went to a local component supplier and got a pair of double sided drives. They worked "out of the box" in DOS, but unsurprisingly, only side 1 of each drive showed up as A: and B: drives.

So I wrote a TSR to add C: and D: drive letterss which were side 2 of each drive.

It was super easy.

Later I heard about a fancier TSR that combined side 1 and 2 of each drive into a single drive letter with twice the capacity.

But that was a much more complicated task, and I was happy enough with my four-drive-letter solution.