CONFIG.SYS (DOS)

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A text file that handles the boot configuration and setup of a DOS operating system, further configuration is then done with another configuration text file called AUTOEXEC.BAT. The main difference between the two is that the boos setup stuff in CONFIG.SYS is something that can only be changed via a hard of soft reboot of the computer while configuration items placed in the AUTOEXEC.BAT file can be changed from the command line while the system is running.

In OS/2 the equivalent file for the DOS subsystem is normally called CONFIG.DOS.

Common CONFIG.SYS commands

BREAK
BUFFERS
The number of buffers DOS reserves for disk access, can be one to 99, the more there are the faster disk access can be but available memory will be lower. If you use a disk caching program this should be set very low.
Options:
n (read ahead buffers, 1 to 9 or 0 to 9 depending on version)
Usage example: BUFFERS=20,2
COMMENT
COUNTRY
DEVICE
Loads a device driver into memory
Options: Driver file name and path
Usage example: DEVICE=C:\DOS\HIMEM.SYS
DEVICEHIGH
Loads drivers into high memory
Usage example: DEVICEHIGH=C:\DOS\ANSI.SYS
DOS
Loads DOS or portions of it into high memory, only works if the HIGHMEM.SYS or comparable driver is present and configured in CONFIG.SYS
Options: HIGH - UMB
Usage example: DOS=HIGH,UMB
DOSDATA
DRIVPARM
FCBS
The number of files control blocks DOS reserves for other users on a network, on a standalone PC this should be 0 unless a program specifically requires otherwise.
Options: None
Usage example: FCBS=30
FILES
The number of files DOS allows applications and shells to have open at once, keep as low as possible since DOS reserves memory space for file handlers. With MS Windows systems running 1.x, 2.x and 3.x, the optimal number of files is around 30, but can be under 10 if Windows and database programs are not used. Some databases and database driven systems like accounting packages can require a much higher number of files open.
Options: None
Usage example: FILES=30
INCLUDE
INSTALL
INSTALLHIGH
LASTDRIVE
Tells DOS to stop searching for drives after a specific drive letter has been found, useful for networked workstations but DOS will continue searching for drive letters indefinitely if this is not used.
Options: None
Usage example: LASTDRIVE=Z
MENUCOLOR
MENUDEFAULT
MENUITEM
MULTITRACK
NUMLOCK
REM
Comment
SET
Sets DOS environment variables
SHELL
Command shell
STACKS
Used to control the behaviour of stack swapping in older versions of DOS, best ignored and left as "STACKS=0,0" unless a program specifically requires anything else.
Options: None
Usage example: STACKS=0,0
SUBMENU
SWITCHES

Outdated commands:

AVAILDEV
usage of \DEV prefix for device names (DOS 2.x)
CPSW
enable code page switching (DOS 4.0)
IFS
installable file system driver (DOS 4.0)
STRING
string substitution buffer (DOS 3.0)
SWITCHAR
default switch character (DOS 2.x)

Common CONFIG.SYS drivers

  • ANSI.SYS - Allows the change of keyboard, graphics and display characters
Options:
/X
/K
/R
Usage example: DEVICE=C:\DOS\ANSI.SYS
  • EMM386.EXE - Expanded memory manager for computers with 386 or newer processors, alternatives existed for 286 and older processors. Allows DOS to access more than 1MB of memory.
Options:
on|off|auto
NOEMS
W=ON|OFF
MIN=size (in kb)
M x (x = address in hex)
FRAME=address (in hex)
/P mmmm (mmmm = adress in hex)
P n = address (in hex)
X=mmmm-nnnn
i=mmmm-nnnn
L= minXMS
A= altregs
H= handles
D=nnn
RAM=mmmm-nnnn
NOVCPI
HIGHSCAN
VERBOSE
WIN=mmmm-nnnn
NOHI
ROM=mmmm-nnnn
NOMOVEXBDA
ALTBOOT
Usage example: DEVICE=C:\Windows\EMM386.EXE NOEMS
  • HIMEM.SYS - Allows the loading of a device drivers into High Memory
Options:
/A20CONTROL:ON|OFF
/CPUCLOCK:ON|OFF
/EISA
/HMAMIN=m
/INT15=xxxx
/NUMHANDLES=n
/MACHINE:xxxx
/SHADOWRAM:ON|OFF
/TESTMEM:ON|OFF
/VERBOSE
Usage example: DEVICE=C:\DOS\HIMEM.SYS /SHADOWRAM:ON /NUMHANDLES=128

Text editors with CONFIG.SYS support

  • Boxer - CONFIG.SYS syntax support included by default - Commercial - OS/2 and DOS versions discontinued, Win32 versions still available.