Expanded Memory Specification


The Expanded Memory Specification (EMS) is a computer memory standard from the 1980s that allowed software to access more memory than was originally possible in DOS-based systems. Developed by Lotus, Intel, and Microsoft, it provided a way for DOS applications to extend beyond the 640KB upper limit. EMS used a window of memory into which it would page in and out larger volumes of data as needed.


The phonetics of the keyword “Expanded Memory Specification” are: eks-pan-did mem-uh-ree speh-suh-fuh-kay-shuhn

Key Takeaways

  1. Expanded Memory Specification (EMS) is a system software specification originally designed to overcome ‘DOS’ 640KB conventional memory limit by enabling the software to access more memory.
  2. It was created as a joint effort by Lotus Software, Intel, and Microsoft. Hence, it’s also known as “The LIM specification” or “LIM EMS” as a nod to the first letter of each of their names.
  3. EMS has gone through several iterations, with ‘EMS 3.2’ being the most common. ‘EMS 4.0’ expanded capabilities further but wasn’t as universally compatible or widely adopted.


The Expanded Memory Specification (EMS) is an important technology term due to its historical significance in computer development. It was specifically crucial during the era of DOS operating systems in the 1980s and early 1990s. EMS allowed computers to access more than the standard 640KB of memory, resolving memory limitations by facilitating access to additional memory area known as “Upper Memory”. In an era where computing resources were very finite, this technology was a crucial development that significantly enhanced computer performance and made new software applications feasible. Even though current technology has surpassed the need for EMS, its role is still acknowledged in the evolution of computer memory management.


The Expanded Memory Specification (EMS) serves a critical purpose in computing environments, particularly those involving older systems. Essentially, EMS was developed to overcome the original 1MB memory limitation evident in Intel’s 8088 and 8086 microprocessors. With the realization that complex, memory-intensive operations demanded more than the restricted 1MB, EMS was introduced to offer a way to reach into additional memory space, beyond the immediate access of the processor.The EMS performs its function by employing a system known as “bank-switching”. It partitions the expanded memory into several “pages”, only one of which could be accessed at any one time. As such, when a program operating in the legacy environment needs to use more memory than the standard limit, EMS helps by creating a window into the expanded memory space, where data can be temporarily stored or retrieved. The introduction of EMS thus extended the capabilities of older systems, allowing them to execute larger, more demanding applications and improve overall system performance.


1. Personal Computer Systems: Many early personal computers, especially those running MS-DOS, used the Expanded Memory Specification (EMS) to increase the amount of memory beyond the typical 640KB limit. For example, systems like the IBM AT would have used expanded memory to run more demanding software applications.2. Gaming Industry: During the early era of PC gaming, some games required EMS to run properly. A popular example is the game ‘Doom’ which used EMS to manage the large amounts of graphic and sound data it needed to load. Doom and many similar games utilized EMS to improve performance and reduce load times.3. Embedded Systems: EMS was used in some embedded systems like ATMs, industrial control systems, or medical equipment that required more memory for complex applications but had limited conventional memory. These systems leveraged EMS to run their resource-demanding applications efficiently while having limited physical memory resources.

Frequently Asked Questions(FAQ)

Q: What is Expanded Memory Specification (EMS)?A: Expanded Memory Specification (EMS) is a technology term referring to a system standard for DOS computers that increases main system memory beyond the conventional limit of 640KB. Q: Who developed Expanded Memory Specification?A: The Expanded Memory Specification was developed by Intel, Lotus Software, and Microsoft in the mid-80s. Q: What is the purpose of EMS?A: The main purpose of EMS was to overcome the original 640KB memory limitation of the IBM PC architecture. Q: Can I use EMS on modern computers?A: No. EMS is characteristic of older, DOS-based systems and isn’t compatible with modern operating systems which have their own ways of handling memory. Q: What is the difference between EMS and XMS (Extended Memory Specification)?A: While both EMS and XMS serve the purpose of overcoming the memory limitation of DOS interfaces, they differ in their approach. EMS makes use of a portion of memory known as the Upper Memory Block (UMB) to create the illusion of more memory, while XMS takes advantage of 80286 and later processors’ ability to directly address more than 1 megabyte of memory.Q: What software applications were able to utilize EMS?A: Many high-end, memory-intensive software applications from the DOS era were designed to utilize EMS including video games, spreadsheets, and word processors. Q: What operating systems support EMS?A: EMS was primarily supported by Microsoft’s MS-DOS, but also by other DOS-compatible operating systems like IBM PC DOS, DR DOS, etc. Q: Can I manually configure EMS on an old DOS-based system?A: Yes, configuration instructions are generally available in the system’s user manual, and it often involves adjusting settings in the CONFIG.SYS file on the computer.

Related Finance Terms

  • Lotus/Intel/Microsoft (LIM)
  • High Memory Area (HMA)
  • DOS Protected Mode Interface (DPMI)
  • XMS Driver
  • Upper Memory Blocks (UMBs)

Sources for More Information


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