Editing Expanded memory (section)

=={{anchor|EMS|EMM}}Expanded Memory Specification (EMS)==
[[Lotus Software|Lotus Development]], [[Intel]], and [[Microsoft]] cooperated to develop the EMS standard (aka LIM EMS). The first publicly available version of EMS, version 3.0 allows access of up to 4&nbsp;MiB of expanded memory.{{cn|date=February 2014}} This was increased to 8&nbsp;MiB with version 3.2 of the specification. The final version of EMS, version 4.0 increased the maximum amount of expanded memory to 32&nbsp;MiB and supports additional functionality.

Microsoft thought that bank switching was an inelegant and temporary, but necessary stopgap measure. Slamming his fist on the table during an interview [[Bill Gates]] said of expanded memory, "It's garbage! It's a [[kludge]]! … But we're going to do it". The companies planned to launch the standard at the Spring 1985 [[COMDEX]], with many expansion-card and software companies announcing their support.<ref name="Machrone_1985"/><ref name="pc200801">{{Cite magazine |date=January 2008 |title=The Most Memorable Tech Flops |url=https://books.google.com/books?id=Gr8rWafdWZAC&pg=PA88 |magazine=PC Magazine |pages=88–89 |access-date=2020-09-05}}</ref> [[AST Research]], [[STB Systems]], [[Persyst]], [[Quadram]], and [[Tecmar]] quickly designed EMS-compliant cards to compete with Intel's own Above Board expansion card. By mid-1985 some already called EMS a [[de facto standard]].<ref name="maremaa19850617">{{Cite magazine |last=Maremaa |first=Tom |date=1985-06-17 |title=Board Makers Flock to New Standard |url=https://books.google.com/books?id=FS8EAAAAMBAJ&lpg=PA16&pg=PA30#v=onepage&q&f=true |access-date=2025-05-01 |magazine=InfoWorld |pages=30-34 |volume=7 |issue=24}}</ref>

The first public version of the EMS standard, called EMS 3.0 was released in 1985; EMS 3.0, however, saw almost no hardware implementations before being superseded by EMS 3.2. EMS 3.2 uses a 64&nbsp;KiB region in the upper 384&nbsp;KiB ([[upper memory]] area) divided into four 16&nbsp;KiB pages, which can be used to map portions of the expanded memory.<ref name="Mendelson_1989"/>

Quadram, AST, and [[Ashton-Tate]] created the Enhanced EMS (EEMS) standard. EEMS, a superset of EMS 3.2, allows any 16&nbsp;KiB region in lower RAM to be mapped to expanded memory, as long as it was not associated with interrupts or dedicated I/O memory such as network or video cards. Thus, entire programs can be switched in and out of the extra RAM. EEMS also added support for two sets of mapping registers. These features are used by early DOS multitasker software such as [[DESQview]]. 1987's LIM EMS 4.0 specification incorporated practically all features of EEMS.<ref name="Mendelson_1989"/>

A new feature added in LIM EMS 4.0 was that EMS boards can have multiple sets of page-mapping registers (up to 64 sets). This allows a primitive form of DOS [[Computer multitasking|multitasking]]. The caveat is, however, that the standard does not specify how many register sets a board should have, so there is great variability between hardware implementations in this respect.<ref name="Rosch_1989"/>

The Expanded Memory Specification (EMS) is the specification describing the use of expanded memory. EMS functions are accessible through software [[interrupt]] 67h. Programs using EMS must first establish the presence of an installed expanded memory manager (EMM) by checking for a device driver with the device name '''EMMXXXX0'''.