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- High_memory_area abstract "In Memory management, the high memory area (HMA) is the RAM area consisting of 65520 bytes beyond the upper memory area of an IBM AT or compatible computer.In real mode, the segmentation architecture of the Intel 80286 and subsequent processors identifies memory locations with 16-bit segment and 16-bit offset, which is resolved into a physical address via (segment) x 16 + (offset). Although intended to address only 1 Megabyte (MB) (220 bytes) of memory, segment:offset addresses at FFFF:0010 and beyond reference memory beyond 1 MB (FFFF0 + 0010 = 100000). So this mode can actually address the first 65520 bytes of extended memory as part of the 64 KB range starting 16 bytes before the 1 MB mark—FFFF:0000 (0xFFFF0) to FFFF:FFFF (0x10FFEF). The Intel 8086 and Intel 8088 processors, unable to handle more than 1 MB of memory because they had only 20 address lines, wrapped around at the 20th bit, so that address FFFF:0010 was equivalent to 0000:0000.In order to allow running existing MS-DOS programs which relied on this feature on their newer IBM PC AT computers, IBM added special circuitry on the motherboard to simulate the wrapping around. This circuit was a simple logic gate which could disconnect the microprocessor's 21st addressing line, A20, from the rest of the motherboard. This gate could be controlled, initially through the keyboard controller, to allow running programs which wanted to access the entire RAM.So-called A20 handlers could control the addressing mode dynamically, thereby allowing programs to load themselves into the 1024–1088 KB region and run in real mode. The first user of the HMA among Microsoft products was Windows/286 2.1 in 1988, which introduced the HIMEM.SYS device driver. Starting with versions 5.0 of DR-DOS (1990) and of MS-DOS (1991), parts of the operating system could be loaded into HMA as well, freeing up to 46 KB of conventional memory. Other components, such as device drivers and TSRs, could be loaded into the upper memory area (UMA).".
- High_memory_area thumbnail IBM_PC_Memory_areas.svg?width=300.
- High_memory_area wikiPageID "420223".
- High_memory_area wikiPageLength "2767".
- High_memory_area wikiPageOutDegree "35".
- High_memory_area wikiPageRevisionID "690607929".
- High_memory_area wikiPageWikiLink A20_line.
- High_memory_area wikiPageWikiLink Address_bus.
- High_memory_area wikiPageWikiLink Byte.
- High_memory_area wikiPageWikiLink Category:DOS_memory_management.
- High_memory_area wikiPageWikiLink Category:X86_memory_management.
- High_memory_area wikiPageWikiLink Conventional_memory.
- High_memory_area wikiPageWikiLink DOS_memory_management.
- High_memory_area wikiPageWikiLink DR-DOS.
- High_memory_area wikiPageWikiLink Electronic_circuit.
- High_memory_area wikiPageWikiLink Expanded_memory.
- High_memory_area wikiPageWikiLink Extended_memory.
- High_memory_area wikiPageWikiLink HIMEM.SYS.
- High_memory_area wikiPageWikiLink AT.
- High_memory_area wikiPageWikiLink Intel_80286.
- High_memory_area wikiPageWikiLink Intel_8086.
- High_memory_area wikiPageWikiLink Intel_8088.
- High_memory_area wikiPageWikiLink Keyboard_controller_(computing).
- High_memory_area wikiPageWikiLink Logic_gate.
- High_memory_area wikiPageWikiLink MS-DOS.
- High_memory_area wikiPageWikiLink Megabyte.
- High_memory_area wikiPageWikiLink Memory_management.
- High_memory_area wikiPageWikiLink Motherboard.
- High_memory_area wikiPageWikiLink Random-access_memory.
- High_memory_area wikiPageWikiLink Real_mode.
- High_memory_area wikiPageWikiLink Terminate_and_stay_resident_program.
- High_memory_area wikiPageWikiLink Unreal_mode.
- High_memory_area wikiPageWikiLink Upper_memory_area.
- High_memory_area wikiPageWikiLink Windows_2.1x.
- High_memory_area wikiPageWikiLink X86_memory_segmentation.
- High_memory_area wikiPageWikiLink File:IBM_PC_Memory_areas.svg.
- High_memory_area wikiPageWikiLinkText "HMA".
- High_memory_area wikiPageWikiLinkText "High memory area".
- High_memory_area wikiPageWikiLinkText "high memory area".
- High_memory_area wikiPageUsesTemplate Template:Distinguish.
- High_memory_area wikiPageUsesTemplate Template:FOLDOC.
- High_memory_area subject Category:DOS_memory_management.
- High_memory_area subject Category:X86_memory_management.
- High_memory_area hypernym Area.
- High_memory_area type Place.
- High_memory_area type Redirect.
- High_memory_area type Thing.
- High_memory_area comment "In Memory management, the high memory area (HMA) is the RAM area consisting of 65520 bytes beyond the upper memory area of an IBM AT or compatible computer.In real mode, the segmentation architecture of the Intel 80286 and subsequent processors identifies memory locations with 16-bit segment and 16-bit offset, which is resolved into a physical address via (segment) x 16 + (offset).".
- High_memory_area label "High memory area".
- High_memory_area differentFrom High_memory.
- High_memory_area sameAs Q16995363.
- High_memory_area sameAs Àrea_de_memòria_alta.
- High_memory_area sameAs High_Memory_Area.
- High_memory_area sameAs Área_de_memoria_alta.
- High_memory_area sameAs 고위_메모리_영역.
- High_memory_area sameAs Pamięć_wysoka.
- High_memory_area sameAs m.0117mzjt.
- High_memory_area sameAs High_Memory_Area.
- High_memory_area sameAs High_Memory_Area.
- High_memory_area sameAs Q16995363.
- High_memory_area wasDerivedFrom High_memory_area?oldid=690607929.
- High_memory_area depiction IBM_PC_Memory_areas.svg.
- High_memory_area isPrimaryTopicOf High_memory_area.