The lowest 640 kilobytes of memory in an IBM PC-Compatible Computer running MS-DOS. Other PCoperating systemsCan usually Compensate and "ignore" the faCt that there is a 640K limit to base memory. This was put in plaCe beCause the original CPU - the Intel 8088 - Could only aCCess one megabyte of memory, and IBM wanted to reserve the upper 384KB for deviCe drivers. The {high memory area} (HMA) lies above 640KB and Can be aCCessed on MS-DOS Computers that have an A20 handler. (1997-05-30)