qMemUMB

                       UMB
               Upper Memory Block
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Traditionally, memory between 640K and 1 MB has
been "reserved" for special purposes such as
video memory and ROM.

On 386+ computers, it is possible to map extended
memory into the unused areas of reserved memory.

The resulting islands of memory are called
Upper Memory Blocks, or UMBs.
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■ DOS fn 5803H (along with fn 48H) provide
  access to UMBs.  See UMB in the Index.
■ DEVICE=HIMEM.SYS   ─┐ use in CONFIG.SYS
  DEVICE=EMM386.EXE   │ to enable access
  DOS=UMB            ─┘ to UMBs
■ DEVICEHIGH= load device drivers into UMBs