Date: Wed, 11 Feb 87 12:34:54 EST
From: weiss@linc.cis.upenn.edu (Tom Weiss)
Subject: Making COMMAND.COM Resident for MS-DOS 2.xx: 

As far as I know, there is nothing you can put in your MS-DOS 2.11
config.sys file that will make command.com stay resident.  A reasonable
alternative is to install command.com 'permanently' on a ramdisk.  This
message is a description of an easy technique to do just that.

I have two floppies (A and B) and my ramdisk is C.  You may need to
adjust drive specs below for your system.  Since I usually boot from
a:command.com, I have no shell command in config.sys. 

The technique is quite simple.  Rename your autoexec.bat file as boot.bat. 
Now make a new autoexec.bat file containing the following lines:
    copy command.com c:
    copy boot.bat c:autoexec.bat
    c:command c:\ /p

If you are using a ramdisk installed by running a .com or .exe file, add
your ramdisk installation command at the top of the new autoexec.bat
file.  No matter what kind of ramdisk you have, be sure to enlarge it to
make room for command.com and boot.bat.

Now reboot your system.  Command.com will be installed on your ramdisk,
and should reload from there under all circumstances. 

How it works: When your system boots, it will load command.com normally
from drive A.  Then the autoexec.bat file copies command.com and your
boot file to drive C (the ramdisk).  The next command spawns an inferior
command.com, and tells it to look for itself in C:\ on reloads.  The /p
tells the spawned command.com to act as if it were the top-level
command.com.  This has two effects: 1) It makes the spawned command.com
process the exit command, so that there is no way to accidentally pop it
by typing exit at dos level.  2) It makes it execute autoexec.bat. 

Memory cost: The memory used will be the space on your ramdisk for
command.com and boot.bat, plus about 4K for spawning an inferior command.com.

Comments: When the spawned command.com starts, it looks for autoexec.bat
in the same place you told it to look for itself on reloads (C:\ in the
example above).  However, drive A is still the default drive, so you
should not need to make any changes to your boot.bat file.  If you
desire, you can place the command 'del c:autoexec.bat' at the end of
boot.bat.  On my system this generates a 'batch file missing' error
message at the end of the boot, but causes no difficulties.  Be sure NOT
to delete c:command.com.  You might even want to change it to read-only. 

Tom Weiss  

weiss@eniac.seas.upenn.edu (Arpanet/CSnet)