From: http://www.os2museum.com/wp/?p=685

Hang with early DOS boot sector

While installing various versions of DOS for the DOS history series of
articles, I was faced with a mysterious problem: Some versions of DOS would
hang right away when booting from fixed disk, but not from floppy. I already
knew that DOS 4.x is very sensitive to BIOS stack usage; if a BIOS needs more
than 100 bytes or so of stack to process a disk read request, it will fail to
boot DOS 4.x from fixed disk, even though the same DOS 4.x can access the
same disk just fine when booted from floppy.

