Dos memory?

IBM reserved the uppermost region of the PC memory map for ROM, RAM on peripherals and memory-mapped input/output (I/O). This region is called the UMA and lies above Conventional memory, between 640 KiB and the 1 MB maximum addressable limit of the original PC's 8088 CPU. For example, the monochrome video memory area runs from B000 to B7FF. However, even with video RAM, the ROM BIOS and I/O ports for expansion cards, much of this 384 KiB of address space was unused - even when a 64 KiB window was reserved for the Expanded Memory Specification "frame" address into which EMS RAM was bank-switched. For example, on most PCs, all or most of the area from C800 to EFFF is normally unused.