The lowest 640 kilobytes of memory in an IBM PC-compatible computer running MS-DOS. Other PC operating systems can 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)
