Expanded Memory Specification (EMS) is an add-on system for DOS operating systems that can be used to manage main memory with storage capacities of 1 megabyte (MB) and more.
MemoryEMS works with a memory address area reserved under the DOS operating system, which is divided into 16-KB sections, called pages. For EMS, at least 4 consecutive pages, corresponding to 64 kilobytes (KB), of DOS memory between 640 KB and 1 MB are used. Typically, the address range is between 768 KB and 896 KB. This 64 KB range can be mapped and is known as the Expanded Memory Page Frame. Using a management program, this area can be managed. The EMS area is only supported by programs that take this area into account, for example Lotus 123 and WordPerfect 5.x.