high memory area

(storage)(HMA) The first 64 kilobytes (minus 16 byte) ofthe extended memory on an IBM PC. By a strange designglitch the Intel 80x86 processors can actually address 17*64kbyte minus 16 byte of memory (from 0000:0000 to ffff:ffff) inreal mode. In the Intel 8086 and Intel 8088 processors,unable to handle more than 1 megabyte of memory, addressingwrapped around, that is, address ffff:0010 was equivalent to0000:0000. For compatibility reasons, later processors stillwrapped around by default, but this feature could be switchedoff. Special programs called A20 handlers can control theaddressing mode dynamically, thereby allowing programs to loadthemselves into the 1024--1088 kbyte region and run in real mode. From version 5.0 parts of MS-DOS can be loaded intoHMA as well freeing up to 46 kbytes of conventional memory.

单词	high memory area
释义	high memory area high memory area (storage)(HMA) The first 64 kilobytes (minus 16 byte) ofthe extended memory on an IBM PC. By a strange designglitch the Intel 80x86 processors can actually address 17*64kbyte minus 16 byte of memory (from 0000:0000 to ffff:ffff) inreal mode. In the Intel 8086 and Intel 8088 processors,unable to handle more than 1 megabyte of memory, addressingwrapped around, that is, address ffff:0010 was equivalent to0000:0000. For compatibility reasons, later processors stillwrapped around by default, but this feature could be switchedoff. Special programs called A20 handlers can control theaddressing mode dynamically, thereby allowing programs to loadthemselves into the 1024--1088 kbyte region and run in real mode. From version 5.0 parts of MS-DOS can be loaded intoHMA as well freeing up to 46 kbytes of conventional memory. AcronymsSeeHMA
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