Epson Progression Setup Manual page 57

Reserved memory is memory in the range 640KB to 1MB. The
system enhances its performance by using 256KB of this
memory as shadow RAM. Some of the remaining memory may
be available; see Appendix A of the User's Guide for information
on how your computer uses this memory.
Extended memory is memory with addresses in the range 1MB to
the maximum system memory, and can be used only by the
following:
applications.
Most MS-DOS commands and application programs cannot use
extended memory directly. They need to use expanded memory.
This type of memory allows some MS-DOS applications to get
around the 640KB limitation. You control expanded memory
with a memory manager, which enables the computer to use
your extended memory as expanded memory.
Most versions of MS-DOS include a standard memory manager
and many application programs come with their own. Once
expanded memory is created, it can be used by MS-DOS
applications written for the Lotus®/Intel®/Microsoft (LIM)
Expanded Memory Specification (EMS), version 4.0.
A-Z Using Memory