[viler]

Part of that was used for option ROMs like hard drive controllers, the EGA/VGA BIOS, network adapters, and for EMS; other areas were just marked by IBM as "reserved", which might have scared people off. In early machines there probably wasn't much of anything there, but then video memory needs were still modest enough that A000-BFFF sufficed.

Probably a good thing, because then those 'holes' could be used for UMBs...