Texas Instruments TravelMate 4000M User Reference Manual page 261

Memory Device Drivers
Some applications may require "backfill" memory, which is
the unused area of standard memory that can be used by
as Expanded memory. For example, an
EMM386.EXE
application may require only 256 KB or 512 KB of standard
memory, leaving 384 KB and 128 KB of backfill memory
space, respectively, for use as Expanded memory.
The Shadow memory that you define with the Setup
ROM
Program enables mapping the internal system BIOS, Video
BIOS, and option BIOS into high-speed memory for faster
operation. When not selected, the shadow memory is
available for use as Extended memory. The shadow memory
area is limited to 384 KB.
(main memory)
Your computer provides 4 MB of
RAM
standard. The first MB (1024 KB) of the standard 4 MB is
the system base memory (640 KB) and shadow memory
(384 KB) and cannot be increased beyond 1024 KB. You
can optionally add 4 MB or 16 MB of memory to use as
Extended and/or Expanded memory. This added memory
when combined with the remaining standard 3 MB (4 MB -
1024 KB) of system memory (not used for base or shadow
memory) provides either 7 MB or 19 MB, respectively, of
Extended or Expanded memory.
See the Microsoft MS-DOS User's Guide and Reference for
detailed instructions on installing and configuring
expanded memory.
HIMEM.SYS
is an eXtended Memory Manager ( )
HIMEM.SYS XMM
conforming to eXtended Memory Specifications ( ), version
XMS
3.04. uses 64 KB of the high-memory area ( )
HIMEM.SYS HMA
at the beginning of Extended memory to store a single
TSR
program or device driver, or it uses this area for data storage.
This effectively increases the size of standard memory for use
by your main application.
Configuring Memory F-7