A CDE Definition
(High Memory Area) In PCs, the first 64K of extended memory from 1024K to 1088K, which can be accessed by DOS. It is managed by the HIMEM.SYS driver. It was discovered by accident that this area could be used by DOS, even though it was beyond the traditional one-megabyte barrier. See PC memory.
(1) The main memory in a PC, which is made up of dynamic RAM chips. Definition #2 outlines the structure of memory in a PC, much of which was of importance to users back in the 1980s, but has long since been an issue. See memory module, SDRAM and dynamic RAM.
(2) The original PC design was constrained to one megabyte of memory. In addition, certain parts of the operating system were placed into fixed locations in the upper part of memory without any method for cooperatively storing additional drivers and programs. This design gave rise to the most confusing platform in history. Windows 3.0 became very popular because it handled all of the memory types much better than DOS.
Following are the different types of memory in a PC. In other computers, there is just plain memory. In mainframes and supercomputers, there are also large, auxiliary memory banks that function as caches between disk and RAM. See PC memory map.
Memory Type Location
Conventional First 640K
UMA (Upper Memory Area) Next 384K
HMA (High Memory Area) Next 64K
Extended Memory From 1MB up
EMS (Expanded Memory) Early spec
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