<
storage> (
HMA) The first 64
kilobytes (minus 16 byte) of
the
extended memory on an
IBM PC. By a strange design
glitch the
Intel 80x86 processors can actually address 17*64
kbyte minus 16 byte of memory (from 0000:0000 to ffff:ffff) in
real mode. In the
Intel 8086 and
Intel 8088 processors,
unable to handle more than 1
megabyte of memory, addressing
wrapped around, that is, address ffff:0010 was equivalent to
0000:0000. For compatibility reasons, later processors still
wrapped around by default, but this feature could be switched
off. Special programs called
A20 handlers can control the
addressing mode dynamically, thereby allowing programs to load
themselves into the 1024--1088 kbyte region and run in {real
mode}. From version 5.0 parts of
MS-DOS can be loaded into
HMA as well freeing up to 46 kbytes of
conventional memory.
(1995-01-10)