eXtended Memory Specification (Reference: DOS, LIM)

eXtended Multiprocessor operating System (Reference: OS)

<storage> Extended Memory Specification. (1996-01-10)

The Cray XMS was a vector processor minisupercomputer sold by Cray Research from 1990 to 1991. The XMS was originally designed by Supertek Computers Inc.

<storage> Memory above the first megabyte of address space in an IBM PC with an 80286 or later processor. Extended memory is not directly available in real mode, only through EMS, UMB, XMS, or HMA; only applications executing in protected mode can use extended memory directly. In this case, the extended memory is provided by a supervising protected-mode operating system such as Microsoft Windows. The processor makes this memory available through a system of global descriptor tables and local descriptor tables. The memory is "protected" in the sense that memory assigned a local descriptor cannot be accessed by another program without causing a hardware trap. This prevents programs running in protected mode from interfering with each other's memory. A protected-mode operating system such as Windows can also run real-mode programs and provide expanded memory to them. DOS Protected Mode Interface is Microsoft's prescribed method for an MS-DOS program to access extended memory under a multitasking environment. Having extended memory does not necessarily mean that you have more than one megabyte of memory since the reserved memory area may be partially empty. In fact, if your 386 or higher uses extended memory as expanded memory then that part is not in excess of 1Mb. See also conventional memory. (1996-01-10)

<software, storage> (XMM) The memory manager software implementing Extended Memory Specification, such as HIMEM or QEMM386. XMM's can usually also act as A20 handlers. (1996-01-10)

<storage> (UMB) Up to 64 kilobytes of the {expanded memory page frame} above the first 64 kilobytes. The UMB can be used to store TSR programs or device drivers thereby freeing parts of the precious conventional memory. The UMB is provided by special memory manager programs; many EMMs can provide UMB as well. (1996-01-10)

<storage> (XMS) The specification describing the use of {IBM PC} extended memory in real mode for storing data (but not executable code). Memory is made available by {extended memory manager} (XMM) software. The XMM functions are accessible through interrupt 2FH. (1996-01-10)

In DOS memory management, extended memory refers to memory above the first megabyte (220 bytes) of address space in an IBM PC or compatible with an 80286 or later processor. The term is mainly used under the DOS and Windows operating systems.

In DOS memory management, the upper memory area (UMA) refers to memory between the addresses of 640 KB and 1024 KB (0xA0000–0xFFFFF) in an IBM PC or compatible. IBM reserved the uppermost 384 KB of the 8088 CPU's 1024 KB address space for BIOS ROM, Video BIOS, Option ROMs, video RAM, RAM on peripherals, memory-mapped I/O, and obsoleted ROM BASIC.