EMS & EEMS

EEMS
A competing standard to EMS is EEMS, developed by Ashton-Tate, AST Research and Quandram.

Extended Memory
Extended Memory is not configurable and unavailable to programs other than those that run in Microsoft Windows and OS/2. 

Expanded Memory
Expanded Memory utilizes EMS and allows DOS programs and other programs to take advantage of the available memory above 1MB.

Expanded Memory Specification (EMS)
Short for Expanded Memory Specification, EMS is a specification that allows IBM compatible computers to access more than the 1MB.  Early IBM compatible computers running MS-DOS used 640KB (conventional memory) + 384KB (Upper Memory) = 1024KB or 1MB total memory for MS-DOS programs. EMS allowed computer programs to access memory above that 1MB. However, because of out of memory issues still being encountered by users, LIM EMS was created.

Extended Memory Specification (XMS)
Developed by AST, Intel, Lotus and Microsoft, XMS is short for eXtended Memory Specification and allows software access to more than one 1MB.

Also see: DPMI, EMM, Memory definitions, LIM EMS, Protected mode