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(operating system)
A text file containing special system configuration commands. It is found in the root directory on an MS-DOS computer, typically on drive C (the hard disk). It is read by MS-DOS at boot time, after the setup has been read from CMOS RAM and before running AUTOEXEC.BAT. It can be modified by the user.

Some example commands which CONFIG.SYS might contain are:

DEVICE=C:\DOS\HIMEM.SYS /testmem:off

Load the extended memory manager.


Load the expanded memory manager.


Specify memory for disk buffers.


Set the number of files that can be open at once.


DOS is located in UppeMemoryBlock.


Disk drives are A: to Z:.


Set the number of file control blocks.


Report the DOS version to older programs.


DOS should maintain a link to UMB.


Set the country code for some programs.


Set dynamic stacks for hardware control.


Set the location of the command interpreter.
This article is provided by FOLDOC - Free Online Dictionary of Computing (


(CONFIGure SYStem) A text file that contained commands to load drivers and establish settings in a DOS PC. Along with AUTOEXEC.BAT, it resided in the root folder. CONFIG.SYS was included in Windows versions for DOS compatibility and was replaced with CONFIG.NT in 32-bit versions of Windows starting with Windows NT. Users could easily make changes, and installation programs sometimes modified CONFIG.SYS for their own purposes.

The following CONFIG.SYS example primarily loads memory managers that were essential to squeeze programs into every byte of what little RAM there was at the time. See AUTOEXEC.BAT, UMA, HIMEM.SYS and EMM386.EXE.
 Driverdevice=c:\dos\himem.sys       RAM > 1MB
 device=c:\dos\emm386.exe ram  EMS memory
 device=c:\dos\ansi.sys        screen/KB
 device=c:\mouse\mouse.sys     mouse
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References in periodicals archive ?
In all cases, the same start-up configuration (AUTOEXEC.BAT and CONFIG.SYS files) was used.
The function of the CTRL-C and CTRL-BREAK key sequences can be disabled by using a software program (BREAK)(4) --the line, "DEVICE=BREAK.SYS/C" is included in the CONFIG.SYS file; (note that the DOS "break=on/off" command does nothing but tell DOS how often it should check for the CTRL-C/CTRL-BREAK key commands, it does not disable those key commands).
After the system has loaded the three programs, it will look for a file called CONFIG.SYS that specifies variable parameters for certain operating conditions.
The manual should show what's loaded on the machine and its configuration: the AUTOEXEC.BAT, CONFIG.SYS, etc.
A CONFIG.SYS is a hidden system file on your C: drive that loads hardware device drivers used by Windows or MS-DOS.
I couldn't get an answer until I persuaded the third person to whom I spoke to read me the line from the CONFIG.SYS file that specifies the name of the device driver software for the CD-ROM.
The commands used in the CONFIG.SYS file, however, are more arcane than self-explanatory.
I especially appreciated it indicating what modifications were made to my Config.sys file.
You need to add the ALLEMM4.SYS driver to your CONFIG.SYS file and make some modifications to the AUTOEXEC.BAT File.
This feature can be activated by including the command "DEVICE = ANSI.SYS" in the "CONFIG.SYS" file (found in the main or root directory) and then rebooting the computer.
It means making sure your sound card and CD-ROM drive are correctly configured in the config.sys file.
For instance, a LASTDRIVE statement in CONFIG.SYS must reflect the last drive letter to be assigned to the PC and the SHARE.EXE program must be run to allow file sharing.