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CONFIG.SYS is the primary configuration file for the DOS and OS/2 operating systems. It is a special ASCII text file that contains user-accessible setup or configuration directives evaluated by the operating system's DOS BIOS (typically residing in
IBMBIO.COM IBMBIO.COM is a system file in many DOS operating systems. It contains the system initialization code and all built-in device drivers. It also loads the DOS kernel (IBMDOS.COM) and optional pre-loadable system components (like for disk compress ...
or
IO.SYS is an essential part of MS-DOS and Windows 9x. It contains the default MS-DOS device drivers (hardware interfacing routines) and the DOS initialization program. Boot sequence In the PC bootup sequence, the first sector of the boot disk is ...
) during boot. CONFIG.SYS was introduced with DOS 2.0.


Usage

The directives in this file configure DOS for use with devices and applications in the system. The CONFIG.SYS directives also set up the memory managers in the system. After processing the CONFIG.SYS file, DOS proceeds to load and execute the command shell specified in the SHELL line of CONFIG.SYS, or
COMMAND.COM COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init proc ...
if there is no such line. The command shell in turn is responsible for processing the
AUTOEXEC.BAT AUTOEXEC.BAT is a system file that was originally on DOS-type operating systems. It is a plain-text batch file in the root directory of the boot device. The name of the file is an abbreviation of "automatic execution", which describes its funct ...
file. CONFIG.SYS is composed mostly of name=value directives which look like variable assignments. In fact, these will either define some tunable parameters often resulting in reservation of memory, or load files, mostly
device driver In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and ot ...
s and TSRs, into memory. In DOS, CONFIG.SYS is located in the
root directory In a computer file system, and primarily used in the Unix and Unix-like operating systems, the root directory is the first or top-most directory in a hierarchy. It can be likened to the trunk of a tree, as the starting point where all branches ...
of the drive from which the system was booted. The filename is also used by (DCP), an MS-DOS derivative by the former East-German VEB Robotron. Some versions of DOS will probe for alternative filenames taking precedence over the default CONFIG.SYS filename if they exist: While older versions of
Concurrent DOS Multiuser DOS is a Real-time operating system, real-time multi-user multi-tasking operating system for IBM Personal Computer, IBM PC-compatible microcomputers. An evolution of the older Concurrent CP/M-86, Concurrent DOS and Concurrent DOS 386 ...
3.2 to 4.1 did not support CONFIG.SYS files at all, later versions of
Concurrent DOS 386 Multiuser DOS is a real-time multi-user multi-tasking operating system for IBM PC-compatible microcomputers. An evolution of the older Concurrent CP/M-86, Concurrent DOS and Concurrent DOS 386 operating systems, it was originally developed by ...
and Concurrent DOS XM, as well as Multiuser DOS, System Manager and REAL/32 will probe for CCONFIG.SYS (with "C" derived from "Concurrent") instead of CONFIG.SYS. Some versions of Multiuser DOS use a filename of CCONFIG.INI instead, whereas REAL/32 is known to look for MCONFIG.SYS. These operating systems support many additional and different configuration settings (like INIT_INSTALL) not known under MS-DOS/PC DOS, but they are stored in the binary repository named CCONFIG.BIN rather than in CCONFIG.INI. Both files are typically modified through a configuration utility named CONFIG.EXE only. Under DR DOS 3.31, PalmDOS 1.0,
Novell DOS DR-DOS (written as DR DOS, without a hyphen, in versions up to and including 6.0) is a disk operating system for IBM PC compatibles. Upon its introduction in 1988, it was the first DOS attempting to be compatible with IBM PC DOS and MS-D ...
 7, OpenDOS 7.01, and DR-DOS 7.02 and higher, a file named DCONFIG.SYS (with "D" derived from "DR DOS"), if present, will take precedence over CONFIG.SYS. Since DR DOS 6.0 this was used in conjunction with disk compression software, where the original boot drive C: would become drive D: after loading the compression driver (and the "D" in the file name came in handy as well), but it is commonly used to help maintain multiple configuration files in multi-boot scenarios. In addition to this, OpenDOS 7.01 and DR-OpenDOS 7.02 will look for a file named ODCONFIG.SYS, whereas some issues of DR-DOS 7.02 and higher will instead also look for DRCONFIG.SYS. Further, under DR DOS 6.0 and higher, the SYS /DR:ext command can be used to change the default file extensions. For example, with SYS /L /DR:703 the written Volume Boot Record would look for a renamed and modified IBMBIO.703 system file (instead of the default
IBMBIO.COM IBMBIO.COM is a system file in many DOS operating systems. It contains the system initialization code and all built-in device drivers. It also loads the DOS kernel (IBMDOS.COM) and optional pre-loadable system components (like for disk compress ...
) and the IBMBIO.703 would look for IBMDOS.703 and ONFIG.703 (instead of
IBMDOS.COM IBMDOS.COM is the filename of the DOS kernel. Loaded and initially invoked by the DOS BIOS in IBMBIO.COM during the boot process, it contains the hardware-independent parts of the operating system, including the embedded FAT12, FAT16 and ...
and ONFIG.SYS), so that multiple parallel sets of files can coexist in the same root directory and be selected via a boot-loader like LOADER, supplied with Multiuser DOS and DR-DOS 7.02/7.03. The SHELL directive is enhanced to provide means to specify alternative AUTOEXEC.BAT files via /P filename.ext/kbd> and in this specific scenario, COMMAND.COM will accept file extensions other than ".BAT" as well (both features are also supported by
4DOS 4DOS is a command-line interpreter by JP Software, designed to replace the default command interpreter COMMAND.COM in Microsoft DOS and Windows. It was written by Rex C. Conn and Tom Rawson and first released in 1989. Compared to the default, ...
). Under DR DOS 6.0 and higher, the CONFIG.SYS directive CHAIN=filespec can be used to continue processing in the named file, which does not necessarily need to reside in the root directory of the boot drive. DR-DOS 7.02 and higher optionally support an additional parameter as in CHAIN=filespec,label to jump to a specific :label in the given file. DR-DOS 7.03 and higher support a new SYS /A parameter in order to copy the corresponding CONFIG.SYS and AUTOEXEC.BAT files along with the system files. FreeDOS implements a similar feature with its FDCONFIG.SYS configuration file.
RxDOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicatio ...
 7.24 and higher use RXCONFIG.SYS instead.
PTS-DOS PTS-DOS (aka PTS/DOS) is a disk operating system, a DOS clone, developed in Russia by PhysTechSoft and Paragon Technology Systems. History and versions PhysTechSoft was formed in 1991 in Moscow, Russia by graduates and members of MIPT, infor ...
uses CONFIG.PTS. Both CONFIG.SYS and AUTOEXEC.BAT can be found included in the root folder of Windows 95, and Windows 98 boot drives, as they are based on DOS. Typically, these files are left empty, with no content. Windows ME does not even parse the CONFIG.SYS file during the Windows boot process, loading environment variables from the Windows Registry instead: : : HKLM\System\CurrentControlSet\Control\SessionManager\Environment Under FlexOS, CONFIG.SYS is a binary file defining the resource managers and device drivers loaded.


Directives


:;*?!

; : Defines labels in CONFIG.SYS as jump targets for , , , and directives. ; : Similar to , but can be used also for in-line comments (following other CONFIG.SYS directives). See . (Under MS-DOS/PC DOS the inline-comment is not ignored if put in double-quotes.) ; : Used to lead in in-line comments in addition to the ; directive. ; : Displays a Yes/No query and (since DR DOS 5.0) optional message to ask the user for confirmation to execute the following CONFIG.SYS directives. (FreeDOS does not support optional messages, but optional conditions in conjunction with boot menus defined with and .) (DOS 6.0 and higher supports a similar feature by adding a after the corresponding CONFIG.SYS directive, f.e. or instead of . This variant is also supported by DR DOS.) ; : Unconditionally execute the following CONFIG.SYS directive.


AC

; : Specifies if programs can be aborted on errors. ; : Configures which drives should store file access date stamps in the reserved area of directory entries in FAT file systems. ; : Conditional execution on AT-compatible machines only. ; : Boot manager. ; : Configures verbosity of error messages. ; : Changes internal default serial device driver ( to ) for device. ; : Disables the availability of character devices outside phantom \DEV directory. ; : Loads base device driver into memory. ; : Emits a short beep, even if audible notifications are disabled via . ; : Specifies operating system to be booted. ; : Sets or clears extended checking. ; : Specifies the number of disk buffers to allocate. ; : Same as , but explicitly loads buffers into HMA or UMB (like under DR DOS 6.0 and higher). ; : Maximum number of 512-byte cache blocks dynamically allocated from system pool. ; : Maximum time in ms before unused cache blocks are returned to system pool. ; : Maximum time in ms before a dirty cache block gets flushed to disk. ; : Similar to under DOS, loads programs in CONFIG.SYS. Similar to under OS/2, but runs in foreground and halts CONFIG.SYS processing until return. ; : Specifies whether the keyboard status is turned on or off. ; : Specifies the name of the CD-ROM hardware driver. ; : Specifies the number of buffers for CD-ROM access. ; : Continues CONFIG.SYS processing in new file and (since DR-DOS 7.02) at optional label. ; : Specifies the type of clock used by the system. ; : Clears screen. ; : Specifies the OEM codepage(s). ; : Specifies the address of the CMOS RAM. ; : Specifies colors for boot menus. ; : Defines count and logical order and configures I/O address and timeout for COM1: device. ; : Defines count and logical order and configures I/O address and timeout for COM2: device. ; : Defines count and logical order and configures I/O address and timeout for COM3: device. ; : Defines count and logical order and configures I/O address and timeout for COM4: device. ; : Specifies buffer for DMA. ; : Redefines the lead-in character(s) for CONFIG.SYS inline-comments, or causes the following line to be ignored. ; : Enables and configures international support. ; : Sets display cursor to specified position for configuration menus. ; : For codepage switching support. ; : Specifies RAM refresh speed. ; : Conditional execution on 8088 CPUs only. ; : Conditional execution on 8088 and higher CPUs only. ; : Conditional execution on 8086 CPUs only. ; : Conditional execution on 8086/8088 and higher CPUs only. ; : Conditional execution on 286 CPUs only. ; : Conditional execution on 286 and higher CPUs only. ; : Conditional execution on 386 and higher CPUs only, f.e. or ; : Conditional execution on 386 and higher CPUs only. ; : Conditional execution on 486 CPUs only. ; : Conditional execution on 486 and higher CPUs only.


DF

; : Configures the relocation of the drive descriptor tables. ; : Specifies the memory segment address up to which multi-sector disk data
deblocking A deblocking filter is a video filter applied to decoded compressed video to improve visual quality and prediction performance by smoothing the sharp edges which can form between macroblocks when block coding techniques are used. The filter aims ...
is allowed. ; : Enables internal debugger support. ; : Boot manager. ; : Loads a device driver into memory. ; : Loads a device driver into upper memory. (Same as in DRDOS 5.0.) ; : Configures country and codepage information for KBD, SCR, LPT1, LPT2, LPT3 devices. ; : Configures cache memory sizes. ; : Specifies floppy disk compatibility mode. ; : Specifies display font. ; : Specifies whether to load DOS into the high memory area and/or use upper memory. (Similar to under DRDOS 5.0.) ; : Specifies whether to load DOS tables (, , , , ) into upper memory. ; : Specifies alternative path to search for DOS files. ; ; : Specifies the search path for data files. ; : Specifies physical parameters of disk drives. ; : Define parameters for unrecognized drives. ; : See . ; : Enables and specifies drive for PDUMP.nnn error logs. ; : Displays a message on screen. ; : Displays a message including ANSI Escape sequences. ; : Specifies if additional checks should be carried out when starting programs. ; : Specifies an error / return code to be assumed in the following. ; : Specifies the state of the
A20 gate The A20, or address line 20, is one of the electrical lines that make up the system bus of an x86-based computer system. The A20 line in particular is used to transmit the 21st bit on the address bus. A microprocessor typically has a number o ...
when starting a program. ; : Finishes CONFIG.SYS processing before the end of the file has been reached (except for and directive processing under some conditions). ; : Specified the size of the hash table for fast file open operations. Works considerably differently from the external MS-DOS/PC DOS
FASTOPEN In computing, FASTOPEN is a DOS terminate-and-stay-resident command, introduced in MS-DOS version 3.3, that provides accelerated access to frequently-used files and directories. The command is also available in SISNE plus. Overview The command wo ...
driver. ; : Specifies the number of cached FCBs that can be opened at once. (Under DR-DOS, and dynamically share the same internal buffer.) ; : Same as , but explicitly loads FCBs into upper memory. ; : Boot manager. ; : Specifies the number of files that can be opened at once. ; : Same as , but explicitly loads file handles into upper memory. ; : Include execution of specified CONFIG.SYS subsections. See .


GI

; : Waits for key (or timeout) and sets error level to its ASCII code (or 1024 on timeout). ; : Continues CONFIG.SYS processing at specified label. ; : Continues nested CONFIG.SYS processing at specified label, with returning to old location. ; : See or or . ; : See . ; : See . ; : See or . ; : See or . ; : See . ; : Installs a TSR program into memory, like , but installs after the DOS data segment relocation. Compare also:
INSTCDEX MSCDEX or Microsoft CD-ROM Extensions is a Computer program, software program produced by Microsoft and included with MS-DOS 6.x and certain versions of Microsoft Windows, Windows to provide CD-ROM support. Earlier versions of MSCDEX since ...
. ; : See or or . ; : See . ; : See or . ; : Enables and configures console and command line history buffer and extended pattern search functionality. ; : Specifies the address of the HMA segment. ; : Configures HLT energy saving. ; : Specifies if the system should check for boot sector viruses. ; : Loads installable file systems. ; : Exclude execution of specified CONFIG.SYS subsections. See . ; : Specifies programs (which would normally run at the CPU's
IOPL In computer science, hierarchical protection domains, often called protection rings, are mechanisms to protect data and functionality from faults (by improving Fault-tolerant design, fault tolerance) and malicious behavior (by providing comput ...
ring 3) which should be allowed to run at ring 2 in order to directly access the hardware for I/O. ; : Include directives from another menu block. (Can be emulated using and under DR-DOS.) ; : Specifies whether the keyboard mode status is turned on or off. ; : Installs a TSR program into memory. ; : Installs a TSR program into upper memory. (Same as in DR DOS 5.0.) ; : Installs a TSR program into memory, like , but installs after the DOS data segment relocation. Compare also:
INSTCDEX MSCDEX or Microsoft CD-ROM Extensions is a Computer program, software program produced by Microsoft and included with MS-DOS 6.x and certain versions of Microsoft Windows, Windows to provide CD-ROM support. Earlier versions of MSCDEX since ...
. ; : Rotates PIC controller interrupt priorities so that specified number gets the highest priority


KM

; : Specifies the keyboard layout. ; : Specifies the address of the relocated keyboard buffer. ; : Specifies the maximum of drives that can be accessed. ; : Same as LASTDRIVE, but explicitly loads the Current Directory Structure (CDS) into upper memory. ; : Specifies a list of search paths for DLLs. ; : Specifies how old programs should be handled. ; : Specifies number of file locks. ; : Configures boot logo support under MS-DOS. Allows to display startup message in conjunction with PTS-DOS boot manager. ; : Defines count and logical order and configures I/O address and timeout for LPT1: device. ; : Defines count and logical order and configures I/O address and timeout for LPT2: device. ; : Defines count and logical order and configures I/O address and timeout for LPT3: device. ; : Enables, defines count and logical order and configures I/O address and timeout for LPT4: device. ; : Specifies time before a waiting process gets a higher priority. ; : Configures memory allocation strategy ; : Specifies the default DOS memory allocation strategy. ; : Defines menu options. ; : Specifies menu colors. (Can be emulated using under DR-DOS.) ; : Specifies the default menu block. (Can be emulated using and under DR-DOS.) ; : Specifies a menu block. (Can be emulated using and under DR-DOS.) ; : Specifies whether multitrack disk operations are used or not. ; : Continues CONFIG.SYS processing in new file (similar to DR-DOS
CHAIN A chain is a serial assembly of connected pieces, called links, typically made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression but linear, rigid, and load-bearing in tension. A c ...
) and optionally after loading a specific device driver and setting %NEWFILE% environment variable.


NQ

; : Specifies the default No () character in Yes/No/Resume questions.) ; : Specifies whether the keyboard status is turned on or off. ; : Conditional execution depending on last return code/error status only, f.e. or . ; : Similar to and under DR-DOS, displays a text and waits for a key press. ; : Specifies if user must acknowledge errors in CONFIG.SYS. ; : Configures buffer size for LPT1, LPT2, LPT3. ; : Conditional execution on PC-compatible machines only. ; : Configures priority scheduler. ; : Configures priority of programs using disk I/O. ; : Changes internal default printer device driver ( to , or even ) for PRN device. ; : Specifies if DOS programs can be run or not. ; : Loads user interface. ; : Conditional execution on PS/1-compatible machines only. ; : Conditional execution on
PS/2 The Personal System/2 or PS/2 is IBM's second generation of personal computers. Released in 1987, it officially replaced the IBM PC, XT, AT, and PC Convertible in IBM's lineup. Many of the PS/2's innovations, such as the 16550 UART (serial po ...
-compatible machines only. ; : Mutes display output send to STDOUT.


RT

; : Specifies if system should reboot automatically on errors. ; : Allows comments in CONFIG.SYS. ; : Specifies a drive letter not to be used up for local block device drivers. ; : Specifies the default Resume () character in Yes/No/Resume queries.) ; : Returns nested CONFIG.SYS processing at previous location of or directive. An optional return code can be given, otherwise 0 is assumed. ; : Defines the real mode memory size. ; : Similar to , loads programs in CONFIG.SYS. Similar to under DOS and under OS/2, but loads programs in background concurrently. ; : Specifies, if the first character of deleted files should be stored in the reserved area of directory entries in the FAT file system. ; : Similar to under PTS-DOS, specifies the video mode to be used under FreeDOS. Under PTS-DOS, does not specify the video mode but screen access methods. ; : Specifies whether the keyboard status is turned on or off.) ; : Sets environment variables. ; : Loads the command interpreter shell. ; : Same as , but supports an additional parameter to define the size of the pre-allocation for COMMAND.COM to relocate its resident portion into the HMA (with /MH). Can be useful to avoid HMA fragmentation in conjunction with third-party shells which cannot load into the HMA. SHELLHIGH under PTS-DOS tries to load the shell into UMBs instead.) ; : Specifies the state of the keyboard modifiers like Shift Lock, Num Lock, Scroll Lock or Insert mode. ; : Specifies if files should be closed on . ; : Specifies if POST should be skipped on reboots. ; : Compatibility dummy - DR DOS 3.31 - 6.0 were mostly reentrant and had a different stacks layout. ; : Specifies the number of stacks for hardware interrupts. ; : Default stack size allocated for new threads. ; : Same as , but explicitly loads buffers into upper memory. ; : Boot manager. ; : Internal use. ; : Specifies how XMS
A20 gate The A20, or address line 20, is one of the electrical lines that make up the system bus of an x86-based computer system. The A20 line in particular is used to transmit the 21st bit on the address bus. A microprocessor typically has a number o ...
control should work. ; : Specifies a submenu block. (Can be emulated using , and under DR-DOS.) ; : Specifies a drive where to log error information instead of displaying a textmode popup screen. ; : Specifies swap file path. ; : Conditionally continues nested CONFIG.SYS processing at one of the specified labels depending on keys pressed, with returning to old location. ; : Defines the default
SwitChar A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
used by the system (either '/' or '-'). ; : Specifies special options. ; : Specifies if a fix for a FPU rounding bug should be activated or not. ; : Specifies file name of alternative DOS operating systems to boot. ; : Configures the location of the various DOS parts in memory. ; : Load system from alternative disk area. ; : Size of system memory pool from which the system dynamically allocates for various purposes ; : Specifies if DOS data and code should be loaded into UMBs. ; : Specifies number of concurrent threads. ; : Specifies the timeouts in CONFIG.SYS single-stepping and with , and , and the default answers for Yes/No queries and selections. PTS-DOS only supports the timeout value. ; : Configures minimum and maximum time slices for scheduler. ; : Specifies the file extension for temporary files. ; : Globally or locally enables or disables CONFIG.SYS (and AUTOEXEC.BAT) single-stepping execution. The functionality under OS/2 differs significantly from that under DOS. ; : Specifies size of log buffer. ; : Logs detailed error information.


UZ

; : Configures DOS management to use a specific segment as UMB memory. ; : Configures the UMB server used. ; : Specifies the address ranges used as UMB RAM. ; : Enables or disables disk write verification. ; : Specifies the DOS version (and optionally the true DOS version) to be reported to programs. ; : Configures VGA display status. ; : Similar to under FreeDOS, specifies current video mode. ; : Specifies if virtual DMA can be used. ; : Specifies if the processor's Virtual Mode Extensions (VME) should be deactivated or not. ; : Configures VxD driver for Windows. ; : Configures system support for Windows. ; : Configures the relocation of the
Extended BIOS data area Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (predicate logic), the set of tuples of values that satisfy the predicate * Exte ...
(XBDA) ; : Conditional execution on XT-compatible machines only. ; : Configures the built-in Year 2000 support. ; : Specifies the default Yes () character in Yes/No/Resume queries. ; : Configures deletion tracking.


Issues

The system can still boot if this file is missing or corrupted. However, this file, along with
AUTOEXEC.BAT AUTOEXEC.BAT is a system file that was originally on DOS-type operating systems. It is a plain-text batch file in the root directory of the boot device. The name of the file is an abbreviation of "automatic execution", which describes its funct ...
, is essential for the complete bootup process to occur with the DOS operating system. These files contain information that is used to customize the operating system for personal use. They also contain the requirements of different software application packages. A DOS system would require troubleshooting if either of these files became damaged or corrupted. If CONFIG.SYS does not contain a SHELL directive (or the file is corrupt or missing), DOS typically searches for COMMAND.COM in the root directory of the boot drive. If this is not found, versions of DOS before 6.0 will not start up. MS-DOS 6.0/PC DOS 6.1 and Novell DOS 7 and higher will instead display a prompt to enter the path and filename of a command processor. This recovery prompt is also displayed when the primary command processor is aborted due to faults or if it is exited deliberately. (In the case of COMMAND.COM, the internal EXIT command is disabled only when the shell was started with /P.) This also provides limited means to replace the shell at runtime without having to reboot the system. Since the MS-DOS 7.0 and higher COMMAND.COM executable is incompatible with DR-DOS, but typically resides in the root of drive C: in dual-boot scenarios with DR-DOS, DR-DOS 7.02 and higher no longer allow to bypass SHELL directives in (+)// "skip"/"trace"/"step" modes. (Some later issues added (+) to reinvoke the former "skip" behaviour in order to allow recovery from problems with invalid SHELL arguments as well.) Also, if no SHELL directive could be found when skipping CONFIG.SYS processing via (+) (and also with (+)/, when the default file extension has been changed with SYS /DR:ext), the user is prompted to enter a valid shell file name ''before'' trying to load COMMAND.COM from the root. Pressing without specifying a file will assume the former default. Depending on the version, the size of the CONFIG.SYS file is limited to a few kilobytes under MS-DOS/PC DOS (up to 64 KB in most recent versions), whereas the file's size is unlimited under DR-DOS. This is because the former operating systems (since DOS 3.0) will compile the file into some tokenized in-memory representation before they sort and regroup the directives to be processed in a specific order (with device drivers always being loaded before TSRs), whereas DR-DOS interprets the file and executes most directives line-by-line, thereby giving full control over the load order of drivers and TSRs via DEVICE and INSTALL (for example to solve load order conflicts or to load a program debugger before a device driver to be debugged) and allowing to adapt the user interaction and change the flow through the file based on conditions like processor types installed, any type of keys pressed, load or input errors occurring, or return codes given by loaded software. This becomes particularly useful since INSTALL can also be used to run non-resident software under DR-DOS, so that temporary external programs can be integrated into the CONFIG.SYS control flow. In MS-DOS/PC DOS 2.0 through 4.01, the length of the SHELL line was limited to 31 characters, whereas up to 128 characters are possible in later versions. DR-DOS even accepts up to 255 characters. CONFIG.SYS directives do not accept
long filename Long filename (LFN) support is Microsoft's backward-compatible extension of the 8.3 filename (short filename) naming scheme used in DOS. Long filenames can be more descriptive, including longer filename extensions such as .jpeg, .tiff, .html, a ...
s.


Dual booting DOS and Windows 9x

When installing Windows 95 over a preexisting DOS/Windows install, CONFIG.SYS and AUTOEXEC.BAT are renamed to CONFIG.DOS and AUTOEXEC.DOS. This is intended to ease dual booting between Windows 9x and DOS. When booting into DOS, they are temporarily renamed CONFIG.SYS and AUTOEXEC.BAT. Backups of the Windows 95 versions are made as CONFIG.W40 and AUTOEXEC.W40 files. When Caldera DR-DOS 7.02/7.03 is installed on a system already containing Windows 95, Windows' CONFIG.SYS and AUTOEXEC.BAT retain those names. DR-DOS' startup files are installed as DCONFIG.SYS (a name already used in earlier versions of DR DOS) and AUTODOS7.BAT.


OS/2 / Windows NT

OS/2 uses the CONFIG.SYS file extensively for setting up its configuration, drivers and environment before the graphical part of the system loads. In the OS/2 subsystem of Windows NT, what appeared as CONFIG.SYS to OS/2 programs was actually stored in the registry. There are many undocumented or poorly documented CONFIG.SYS directives used by OS/2. CONFIG.SYS continues to be used by the OS/2 derivatives eComStation and
ArcaOS ArcaOS is an operating system based on OS/2, developed and marketed by Arca Noae, LLC under license from IBM. It was codenamed Blue Lion during its development. It builds on OS/2 Warp 4.52 by adding support for new hardware, fixing defects and l ...
.


See also

*
IBMBIO.COM IBMBIO.COM is a system file in many DOS operating systems. It contains the system initialization code and all built-in device drivers. It also loads the DOS kernel (IBMDOS.COM) and optional pre-loadable system components (like for disk compress ...
/
IO.SYS is an essential part of MS-DOS and Windows 9x. It contains the default MS-DOS device drivers (hardware interfacing routines) and the DOS initialization program. Boot sequence In the PC bootup sequence, the first sector of the boot disk is ...
*
IBMDOS.COM IBMDOS.COM is the filename of the DOS kernel. Loaded and initially invoked by the DOS BIOS in IBMBIO.COM during the boot process, it contains the hardware-independent parts of the operating system, including the embedded FAT12, FAT16 and ...
/
MSDOS.SYS MSDOS.SYS is a system file in MS-DOS and Windows 9x operating systems. In versions of MS-DOS from 1.1x through 6.22, the file comprises the MS-DOS kernel and is responsible for file access and program management. MSDOS.SYS is loaded by the DOS BI ...
*
CONFIG (environment variable) An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP envi ...
*
AUTOEXEC.BAT AUTOEXEC.BAT is a system file that was originally on DOS-type operating systems. It is a plain-text batch file in the root directory of the boot device. The name of the file is an abbreviation of "automatic execution", which describes its funct ...
*
COMMAND.COM COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init proc ...
* List of DOS commands


Notes


References


External links

* * * (Description of DR-DOS 7 CONFIG.SYS directives (incomplete)) * * * {{DEFAULTSORT:Config.Sys DOS configuration files OS/2 files Configuration files