Upper memory area

<p>In <a href="/facts/DOS_memory_management/EYvgYWs9">DOS memory management</a>, the upper memory area (UMA) is the <a href="/facts/Computer_memory/hQKVQ51J">memory</a> between the <a href="/facts/Address_space/EscyYKkP">addresses</a> of 640 <a href="/facts/Kilobyte/jIe6t4yv">KB</a> and 1024 KB (<a href="/facts/Hexadecimal/02ohQW22">0x</a>A0000–0xFFFFF) in an <a href="/facts/IBM_PC/yhcJGMPL">IBM PC</a> or compatible. IBM reserved the uppermost 384 KB of the <a href="/facts/Intel_8088/DdWKfyBp">8088</a> <a href="/facts/Central_processing_unit/Jxp1bqMV">CPU</a>'s 1024 KB address space for <a href="/facts/BIOS/AYYPUogS">BIOS</a> <a href="/facts/ROM/P9QMuDLH">ROM</a>, <a href="/facts/Video_BIOS/vJSt2EmJ">Video BIOS</a>, <a href="/facts/Option_ROM/NSra8Rl3">Option ROMs</a>, video RAM, <a href="/facts/RAM/DuD4bxh6">RAM</a> on peripherals, <a href="/facts/Memory-mapped_I/O/PmLNFq01">memory-mapped I/O</a>, and obsoleted <a href="/facts/ROM_BASIC/aTec7AQY">ROM BASIC</a>.
</p><p>However, even with video RAM, the ROM <a href="/facts/BIOS/AYYPUogS">BIOS</a>, the <a href="/facts/Video_BIOS/vJSt2EmJ">Video BIOS</a>, the <a href="/facts/Option_ROM/NSra8Rl3">Option ROMs</a>, and I/O ports for peripherals, much of this 384 KB of address space was unused. As the 640 KB memory restriction became ever more of an obstacle, techniques were found to fill the empty areas with RAM. These areas were referred to as upper memory blocks (UMBs).
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Upper memory area open-in-new

Upper memory area