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1993-02-15
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53 lines
Loading COMMAND.COM High
the Ultimate DOS 5.0 Trick
by Alan Motsinger
Pinellas IBM-PCUG - Bits & Bytes
Clearwater, FL
Your SHELL command in CONFIG.SYS probably looks something
like this (Ed Note: command line is all on one line):
Shell=
C:\DOS\Command.Com C:\DOS /e:1024 /p
What if you changed it to look something like this:
Shell=
C:\DOS\Command.Com /C LH C:\Command.Com C:\DOS /e:1024 /p
What would that accomplish? Basically, what you're doing is loading
a temporary copy of COMMAND.COM and telling it to execute a statement
and immediately exit (the /C option). The command just happens to
be LOADHIGH COMMAND.COM. Although, the temporary copy gets "stuck"
in low memory (/C tells the first copy to exit, but the /P on the
high copy makes it permanent, so you can't exit back to the first
to release it), your primary copy of COMMAND.COM is now loaded high.
Your computer finishes the boot process as normal and nothing looks
different, but things are different! The high copy of COMMAND.COM
acts as a doorway to your high memory. Try using a memory mapping
utility such as MAPMEM (TurboPower Software). You'll find that the
map is not only your low memory, but also your high memory. You'll
also notice that any TSR you load from the DOS prompt (even without
LOADHIGH) will automatically become resident in high memory. You'll
notice a few extra K free down in low conventional, and memory access
(compare before and after speeds by looking at CheckIt's Memory Map)
in the high area is quite a bit faster.
What are the drawbacks? The only problems I discovered to date are
related to TSRs, especially ones that try to update their status in
memory (they load fine, but don't try to change them). They tend to
lock up often; however, all major programs that I've tried, run
smoothly - perhaps even a little faster.
Although I am using 4DOS (Command.Com replacement that automatically
loads high except for 256 bytes), this idea does appear to work on
everything I tried. This concept is NOT for the faint of heart,
however, or for those that think they are on the 'leading edge'.
This is for the 'bleeding edge' folks only!
[Ed Note: This was taken from the BBS messages.]