XMS 

 
(1) (eXtended Memory Specification) A programming interface that allows DOS programs to use extended memory in 286s and up. It provides a set of functions for reserving, releasing and transferring data to and from extended memory without conflict, including the high memory area (HMA). See HIMEM.SYS and DOS extender.

XMS, VCPI and DPMI all deal with extended memory. However, XMS allows data and programs to be stored in and retrieved from extended memory, whereas the VCPI and DPMI interfaces allow programs to "run" in extended memory.

 
VCPI 

 
(Virtual Control Program Interface) A programming interface that allowed DOS-extended programs and Real Mode programs to run together in 386s. It was primarily developed by Quarterdeck to allow its DESQview multitasker to run DOS-extended programs. DPMI succeeded VCPI and provided the same capability for Windows.

 
DPMI 

 
(DOS Protected Mode Interface) A programming interface from Microsoft that allows a DOS-extended program to run cooperatively under Windows 3.x. It is not compatible with VCPI, the first DOS extender standard, but Windows 3.1 is more tolerant of VCPI applications than Windows 3.0.

XMS, VCPI and DPMI all deal with extended memory. However, XMS allows data and programs to be stored in and retrieved from extended memory, whereas VCPI and DPMI allow programs to "run" in extended memory.