The following are some rules and "equations" for combining, modifying, and emulating memory to make it useful:
- XMS memory = extended memory + HIMEM.SYS
- XMS memory including UMBS = 80386 system + extended memory + HIMEM.SYS + EMM386.EXE (version 4.33.06x or later)
- XMA memory = proprietary memory adapter of IBM
- EMS memory = usable by MS-DOS and applications
- extended memory = usable by some applications
- XMA memory = 80386 system + extended memory + XMAEM.SYS
- EMS memory = 80386 system + extended memory + EMM386.SYS (version 4.0)
- EMS memory = 80386 system + extended memory + HIMEM.SYS + EMM386.SYS or EMM386.EXE (version 4.10.0419 or later)
This means the two-stage system needed by IBM PC-DOS owners to convert their 80386 extended memory into EMS memory is as follows:
EMS memory = 80386 system + extended memory + XMAEM.SYS + XMA2EMS.SYS
The one state processed is needed by Microsoft MS-DOS users to convert their 80386 systems to EMS memory is as follows:
- EMS memory = 80386 system + extended memory + EMM386.SYS (version 4.0)
- EMS memory = 80386 system + extended memory + HIMEM.SYS + EMM386.SYS (version 4.10.0419)
- EMS memory = 80386 system + extended memory + HIMEM.SYS +
The above applies to:
- Microsoft MS-DOS operating system 2.11
- Microsoft MS-DOS operating system 3.1
- Microsoft MS-DOS operating system 3.2
- Microsoft MS-DOS operating system 3.21
- Microsoft MS-DOS operating system 3.3
- Microsoft MS-DOS operating system 3.3a
- Microsoft MS-DOS operating system 4.0
- Microsoft MS-DOS operating system 4.01
- Microsoft MS-DOS operating system 5.0
- Microsoft MS-DOS operating system 5.0a
- Microsoft MS-DOS operating system 6.0
- Microsoft MS-DOS operating system 6.2
- Microsoft MS-DOS operating system 6.21
- Microsoft MS-DOS operating system 6.22
