When we set the upper limit of PC-DOS at 640K, we thought nobody would ever need that much memory. — William Gates, chairman of Microsoft. Evidently this was mentioned at a 1981 tradeshows originally.
After all, Visicalc operated usefully on a mere 48K Apple II!
My first microcomputer had 12K of memory. When I expanded to a full 64K, I thought I had all the memory I’d ever need. Hah. I know better now.
In 1985, most are now using at least 256MB which is more than enough for MS-DOS. The IBM PC AT is more powerful but it is also more expensive.