• If you have an 80386 system, extended memory, and MS-DOS, you can use EMM386.SYS to obtain EMS memory. If you have the same system and memory with IBM PC-DOS, you must use two drivers, XMAEM.SYS and XMA2EMS.SYS, to achieve EMS memory.
• If you have an 80286 system and want to use your extended memory as EMS memory, you will not be able to use the existing drivers included with MS-DOS. Some of these extended memory boards come with EMS emulators, which can be used.

• The Microsoft driver HIMEM.SYS takes over 80286 and 80386 extended memory, converting it to the extended memory area of the XMS specification. It also takes the first 64K of this extended memory area and converts it into the HMA.
• The IBM PC-DOS version 4.0 driver XMAEM.SYS takes IBM PS/2 Model 80 80386 extended memory and uses it to emulate IBM XMA memory. (Used in conjunction with the XMA2EMS.SYS driver, it is possible to use this memory as EMS memory.)
• The IBM PC-DOS version 4.0 driver XMA2EMS.SYS takes IBM XMA memory (or the emulated XMA memory created by the XMAEM.SYS driver) and uses it to emulate LIM/EMS memory.
• The Microsoft MS-DOS version 4.0 driver EMM386.SYS takes 80386 extended memory and uses it to emulate LIM/EMS memory.

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