Epson 4SLC2-50 - Manual (Page 49)

Extended memory is memory with addresses in the range lMB to
8MB, and is used only by the following:
Certain operating systems, such as OS/2
Some MS-DOS interfaces, such as Windows
Some RAM disk programs, such as VDISK
Some hard disk caching programs, such as SMARTDRV
Certain specially-written MS-DOS applications.
Use of extended memory requires a memory manager. Most
versions of MS-DOS include a standard extended memory
manager. If you are using MS-DOS, Windows, and other
compatible programs, it is best to use one of the memory managers
(such as HIMEM.SYS) that came with your software because these
memory managers have been tested and proven reliable.
Most MS-DOS commands and application programs cannot use
extended memory directly. They need to use expanded memory,
which uses a portion of reserved memory as a window to access
RAM beyond lMB. This type of memory allows some MS-DOS
applications to get around the 640KB size limitation. You control
expanded memory with a memory manager (such as
EMM386.EXE), which enables the computer to use extended
memory as expanded memory.
Using Your Computer 2-17