(Expanded Memory Specification) The first technique that allowed DOS to go beyond its one megabyte memory limit. It allowed access to 32MB of memory by bank switching it through a 64KB buffer (page frame) in the UMA. Either the application was written to use EMS (Lotus 1-2-3 Ver. 2.x, AutoCAD, etc.) or it was run in an environment that did such as DESQview. The first EMS memory in XTs and ATs required an EMS board and driver. When the 386 came out, it could create EMS memory from extended memory.

There used to be tremendous confusion over EMS. Not only did expanded memory (EMS) and extended memory sound alike, but in the early days, you had to allocate how much EMS you needed. Today, EMS is practically unheard of. Windows manages all the memory in the computer and can allocate whatever EMS it needs on the fly for old DOS applications that require it.