The next stage in the evolution of DOS was for the operating system to use upper memory blocks ( UMBs ) and the high memory area ( HMA ).
12.
DOS 5 supported the use of the High Memory Area ( HMA ) and Upper Memory Blocks ( UMBs ) on 80286 and later systems to reduce its conventional memory usage.
13.
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 ).
14.
The extended memory manager is also responsible for managing allocations in the high memory area ( HMA ) and the upper memory area ( UMA; also referred to as upper memory blocks or UMBs ).
15.
The ability of DOS versions 5.0 and later to move their own system core code into the high memory area ( HMA ) through the DOS = HIGH command gave another boost to free memory.
16.
Using a quirk in the 286 CPU architecture, the " high memory area " ( HMA ) was accessible, as the first 64 kB above the 1 MB limit of 20-bit addressing in the x86 architecture.
17.
The " high memory area " ( " HMA " ) is the RAM area consisting of the first 64 KiB, minus 16 bytes, of the extended memory on an IBM PC / AT or compatible microcomputer.
18.
This provided a way to copy data to and from extended memory, access to the 65520-byte High Memory Area ( HMA ) directly above the first megabyte of memory and the Upper Memory Block ( UMB ) area.
19.
First, the DR DOS kernel and structures such as disk buffers can be located in the High Memory Area ( HMA ), the first 64 KB of extended memory which are accessible in real mode due to an incomplete compatibility of the 80286 with earlier processors.
