The old code was essentially a no-op due to x86 taking shifts mod 32.
This lead DOS to believe that it had 10KiB of memory, which is not
enough to contain io.sys, the DOS kernel, and command.com. This causes
command.com to overwrite the DOS kernel when it goes to relocate itself
at the end of the memory, leading to system crash.
Using `dw` ended up shifting all the values over by one byte, making DOS
think our 320K floppy was actually 16MiB in size, and had 46 sectors of
FAT instead of 1. This further lead it trash the setup stack and fail to
locate the disk directory.
Juhani Krekelä