For more information on this, see the article on the Upper Memory Area ( UMA ).
2.
Other components, such as device drivers and TSRs, could be loaded into the upper memory area ( UMA ).
3.
:The real mode address space does not have one standard layout, IBM reserved some memory mapped areas in Upper Memory Area.
4.
The 640 KB barrier is due to the IBM PC placing the Upper Memory Area in the 640 1024 KB range within its 20-bit memory addressing.
5.
The design of the original IBM PC placed the Color Graphics Adapter ( CGA ) memory map and other hardware in the 384 KB upper memory area ( UMA ).
6.
Not all addresses in the upper memory area were used in a typical system; unused physical addresses would return undefined and system-dependent data if accessed by the processor.
7.
In practice the upper memory area will be provided by the expanded memory manager ( EMM ), after which DOS will try to allocate them all and manage them itself.
8.
On IBM XT computers, it was possible to add more memory to the motherboard and use a custom address decoder PROM to make it appear in the upper memory area.
9.
These memory areas are referred to as the high memory area ( HMA ) and the upper memory area ( UMA; also referred to as upper memory blocks or UMBs ).
10.
EMM386 . EXE can map memory into unused blocks in the upper memory area ( UMA ), allowing device drivers and TSRs to be " loaded high ", preserving conventional memory.
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