DOS System Files

The following tip is for MS-DOS file systems. IBM-DOS has their own set of files which I am unfamiliar with. Much of the following may still be helpfull to you, but keep in mind that some file names vary from this listing.
 
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MS-DOS System Files
In order for your system to boot from a drive the files in red need to be present in the root directory of that drive.
msdos.sys Hidden file, [proper attributes +r +s +h] Should be located in the root directory of your bootable drive.
io.sys Hidden file, [proper attributes +r +s +h] Should be located in the root directory of your bootable drive.
command.com Not Hidden [proper attributes + r] Should be located in the root directory of your bootable drive, but may also reside in the Drive:\dos directory if a SHELL=Drive:\dos\command.com command is included in the config.sys file. NOTE: Replace Drive with the actual drive letter being booted from.
sys.com This file will restore the above system files if they are missing on your hard drive. Make a bootable floppy and make sure this file is on it for emergencies.
config.sys This file holds commands to load various device drivers which are needed for your specific system configuration. It also runs commands to set up specific parameters needed by dos to determine how you want your ram used, etc... It is a text file, which means that all commands in it are entered in plain text, do not use a word processor to edit it unless the word processor is capable of saving in plain text mode.
autoexec.bat This file is used to set up certain parameters like the PATH and PROMPT statements, loading memory resident programs, and running programs which are intended to be run once on each boot up. It is a text file, which means that all commands in it are entered in plain text. Do not use a word processor to edit it unless the word processor is capable of saving in plain text mode.
NOTES The above files are a minimum set needed to boot your system. There may be additional files needed to insure that all hardware devices will work. These files will be referenced in commands within your config.sys and autoexec.bat files. One of the more common of these files would be mscdex.exe which is needed for most if not all cd rom drives, and is called from the autoexec.bat file. mscdex.exe is included with MS-DOS and will be found in the \DOS directory.
Files to include on
a rescue disk for
emergencies.		 There are a number of files which will make repairing your system much easier in the case of problems. 
Issue the following list of commands after inserting a blank disk in your A drive:

FORMAT A:
SYS A:  [This will transfer the first three files above to your drive.]
COPY C:\AUTOEXEC.BAT A:\
COPY C:\CONFIG.SYS A:\
COPY C:\DOS\SYS.COM A:\

Now go through your config.sys and autoexec.bat files and look for device drivers and memory resident program files needed to operate your cd rom drives, scsi devices, and mouse. Copy them to the floppy disk, and change the calls to them in the autoexec.bat and config.sys file on your floppy to reflect their new locations. EXAMPLE:

Old line in c:\autoexec.bat -- c:\mouse\mouse.exe /f
New line in a:\autoexec.bat - a:\mouse.exe /f

Also insure that you add the A drive to your path statement in the autoexec.bat file on the floppy.

Other Files Commonly Needed

File Name Location Description
mscdex.exe c:\dos Specifies the ID to use with devices like your CD rom drive to DOS.
emm386.exe c:\dos Used by config.sys to set up usage of ram for your system.
dblspace.sys c:\dos MS-DOS disk compression driver.
dblspace.bin c:\dos Part of MS-DOS disk compression
himem.sys c:\dos Used by DOS to load programs into high memory

Now that you have the basic set needed to boot your system with all the hardware working, let's get a list of other files you may need to make repairs. If necessary you may copy these to a second blank floppy if they won't all fit on the first one.
 
File Name Location Description
edit.com c:\dos MS-DOS editor needed to edit system files.
edit.hlp c:\dos Help for the MS-DOS Editor. Not required, but you might want it.
qbasic.exe c:\dos Needed to run MS-DOS Editor
scandisk.exe c:\dos Checks disks for file allocation table, and physical errors, and fixes them.
fc.exe c:\dos File compare utility. Lets you compare two files and outputs their differences. Handy for diagnosing whether a system file has changed, or been corrupted. Compares both text files, and binary files.
list.com shareware Vern Buerg's List.com is an excellent file viewer, and directory shell program. It will save you a lot of time as it works like a menu for loading files to view, copy, delete, move, or even load into the editor. It's on the net somewhere, if you find it, let me know and I'll post the url here.
format.com c:\dos In case you need to format a disk, or re-format the hard drive.
attrib.exe c:\dos This command sets the attributes for files, and may be needed to clear the system, and read only attributes of a corrupted system file before deleting it.
msd.exe c:\dos Microsoft Diagnostics. Will allow you to view irq settings, etc for system devices on your system.

Keep in mind that you will need to know how to use DOS commands to be totally effective in restoring your system to health. Take some time to learn them by typing HELP at the dos prompt.
C Ray Parrish, Cottage Grove, Oregon