High Memory Area
A 65520-byte area of memory from ffff:0010 to ffff:ffff.
It is available on 286-based and 386+ computers in which
the HIMEM.SYS device driver has been installed.

DOS can load itself into the HMA, freeing up nearly 64K
of conventional memory for use by application programs.
  DOS=HIGH (in CONFIG.SYS) puts DOS in the HMA
  If the HMA has not been taken, it may by used by
TSRs, etc.  See XMS in the Index.
  Part of the HMA may be free; see HMA Suballocations