ACCDATE (CONFIG.SYS directive)

CONFIG.SYS
Company type	Configuration file
Industry	Computer operating systems
Founded	1983
Products	System configuration commands for DOS and OS/2

Adapted from the English Wikipedia article ACCDATE (CONFIG.SYS directive), available under CC BY-SA 4.0Updated 9 August 2025

CONFIG.SYS serves as the main configuration file for DOS and OS/2 operating systems. This plain text file, written in ASCII, holds configuration commands that the operating system's DOS BIOS—typically found in IBMBIO.COM or IO.SYS—processes during system startup. The CONFIG.SYS file was first introduced with DOS version 2.0.

Usage

The directives within CONFIG.SYS tailor DOS settings for hardware devices, software applications, and memory allocation. Once CONFIG.SYS is processed, DOS launches the command interpreter specified by the SHELL directive; if none is specified, it defaults to COMMAND.COM, which subsequently executes AUTOEXEC.BAT.

This file primarily contains name=value pairs that define system parameters or load device drivers and TSR (terminate-and-stay-resident) programs. CONFIG.SYS is located in the root directory of the bootable drive.

Certain DOS versions prioritize alternative filenames:

Concurrent DOS 386, Concurrent DOS XM, Multiuser DOS, System Manager, and REAL/32 search for CCONFIG.SYS or CCONFIG.INI (in Multiuser DOS) and MCONFIG.SYS (in REAL/32). These platforms also utilize additional configuration data stored in binary files such as CCONFIG.BIN, which can be edited using CONFIG.EXE.

In DR DOS 3.31 and subsequent releases—including PalmDOS 1.0, Novell DOS 7, OpenDOS 7.01, and DR-DOS 7.02+—the file DCONFIG.SYS takes precedence over CONFIG.SYS. This naming convention supports scenarios involving disk compression utilities and multi-boot configurations. OpenDOS 7.01 and DR-OpenDOS 7.02 additionally recognize ODCONFIG.SYS, while some DR-DOS editions check for DRCONFIG.SYS. The command SYS /DR:ext enables renaming of system files to accommodate multiple configurations within a single root directory, aiding boot loader selection.

DR-DOS extends the functionality of the SHELL directive by allowing specification of alternate AUTOEXEC.BAT files and introduces the CHAIN=filespec[,label] directive to continue processing configuration files located outside the root folder.

FreeDOS employs FDCONFIG.SYS, RxDOS uses RXCONFIG.SYS, and PTS-DOS relies on CONFIG.PTS for comparable configuration purposes.

Within Windows 95 and Windows 98 environments, CONFIG.SYS and AUTOEXEC.BAT remain in the root directory but are generally left empty since these systems are based on DOS. Windows Me does not parse CONFIG.SYS during startup; instead, it retrieves environment variables from the Windows Registry at:

HKLM\System\CurrentControlSet\Control\SessionManager\Environment

For FlexOS, CONFIG.SYS exists as a binary file that lists resource managers and device drivers to be loaded during boot.

Example

Sample CONFIG.SYS content for MS-DOS 5: <syntaxhighlight lang="ini" line="1"> DOS=HIGH,UMB DEVICE=C:\DOS\HIMEM.SYS DEVICE=C:\DOS\EMM386.EXE RAM DEVICEHIGH=C:\DOS\ANSI.SYS FILES=30 SHELL=C:\DOS\COMMAND.COM C:\DOS /E:512 /P </syntaxhighlight>

:;*?!

: Marks labels within CONFIG.SYS used as jump destinations for , , , and commands.
: Functions similarly to , also serving as inline comments after other directives. (Note: In MS-DOS/PC DOS, inline comments enclosed in double quotes are not ignored.)
: Introduces inline comments alongside ; directives.
: Prompts a Yes/No confirmation with an optional message before executing subsequent CONFIG.SYS commands. (FreeDOS supports conditional execution with boot menus but lacks optional messages.) DOS version 6.0 and later offer comparable functionality by appending after commands (e.g., ).
: Executes the next CONFIG.SYS command without conditions.

ATemplate:NbndC

: Determines whether programs can be terminated upon encountering errors.
: Sets drives to record file access timestamps within FAT file systems.
: Enables conditional execution on AT-compatible hardware.
: Manages the boot process.
: Adjusts the detail level of error message output.
: Alters the default serial port driver (COM1 through COM4) assigned to the AUX device.
: Prevents character devices from being accessible outside the phantom \DEV directory.
: Loads the fundamental device driver into system memory.
: Produces a brief beep sound regardless of notification switch settings.
: Defines the subsequent operating system to boot.
: Activates or deactivates extended Ctrl+C detection.
: Specifies how many disk buffers should be allocated.
: Functions like BUFFERS but places buffers into HMA or UMB areas.
, , (Embedded DOS 6-XL only): Controls cache block allocation, retention duration, and flushing intervals.
: Executes programs listed in CONFIG.SYS, pausing further processing until completion.
(DR-DOS 7.02+): Toggles keyboard Caps Lock status on or off.
, (PTS-DOS only): Sets CD-ROM driver name and buffer quantity.
(DR DOS 5.0+, Embedded DOS): Continues CONFIG.SYS execution within a new file or label section.
, , and other commands adjust system behavior and visual options tailored for various DOS versions.
, (OS/2 only) assigns OEM codepages to support internationalization.

Additional directives cover COM port settings (COM1 through COM4), redefining COMMENT statements, COUNTRY configurations for localization, CPU-specific conditional commands (CPU386, CPU486, etc.), and parameters for loading device drivers aimed at optimizing system performance across multiple DOS platforms.

This extensive directive collection allows organizations to tailor their system startup routines, maximize hardware efficiency, and improve compatibility among a wide range of computing setups.

DTemplate:NbndF

: Manages relocation of drive descriptor tables in memory.
: Defines the memory segment address used for multi-sector disk data deblocking operations.
: Activates built-in debugger functionality.
: Oversees boot management tasks.
: Loads a specified device driver into memory.
: Loads a device driver into upper memory blocks (equivalent to in DRDOS 5.0).
: Configures country code and codepage settings for keyboard, screen, and printer devices.
: Sets sizes for cache memory allocation.
: Determines floppy disk compatibility mode settings.
: Specifies the font used for display output.
: Controls loading of DOS into high memory and/or utilization of upper memory areas (similar to in DRDOS 5.0).
: Loads DOS-related tables (BUFFERS, FCBS, FILES, LASTDRIVE, STACKS) into upper memory regions.
: Specifies an alternative directory path for DOS system files.

: Sets search paths for locating data files.
: Defines physical characteristics of disk drives attached to the system.
: Establishes parameters for drives that are not automatically recognized by the system.
: Refer to .
: Enables error logging via PDUMP.nnn files and designates the target drive for these logs.
: Outputs a message directly on screen display.
: Displays messages incorporating ANSI Escape sequences for enhanced formatting.
: Adds extra verification steps when launching programs.
: Assigns an expected error or return code value for program execution results.
: Configures the A20 gate state during program startup sequences.
: Terminates CONFIG.SYS processing prematurely, except for certain SWITCHES and SHELL directives which continue execution.
: Defines hash table size to accelerate file opening operations, differing from MS-DOS/PC DOS FASTOPEN implementation.
: Specifies number of cached File Control Blocks (FCBs) that can be open simultaneously (shares buffer space with FILES under DR-DOS).
: Similar to FCBS but explicitly loads FCBs into upper memory areas.
: Boot management utility command.
: Sets maximum number of files that can be opened concurrently by the system.
: Functions like FILES but explicitly loads file handles into upper memory blocks.
: Facilitates execution of designated CONFIG.SYS subsections (refer to IGNORE directive).

GTemplate:NbndI

: Waits for a key press or timeout, setting the error level to the ASCII value or 1024 if timed out.
: Resumes processing of CONFIG.SYS at a designated label.
: Continues nested CONFIG.SYS execution at a specified label, then returns to the prior point.
: Refer to , , or for additional information.
: Consult for further details.
: See for more context.
: Refer to or as needed.
: See or for related commands.
: Consult for further reference.
: Loads a TSR program into memory following relocation of the DOS data segment. Also see INSTCDEX.
: Refer to , , or for complementary instructions.
: See for additional options.
: Consult or for related usage.
: Activates console and command line history buffer with enhanced pattern search capabilities.
: Defines the address of the HMA segment.
: Configures the HLT power-saving mode.
: Enables scanning of the boot sector for viruses.
: Loads installable file system drivers.
: Prevents execution of certain CONFIG.SYS subsections.
: Grants specified programs permission to execute at ring 2, allowing direct hardware I/O access.
: Incorporates directives from another menu block (simulated using GOSUB/RETURN in DR-DOS).
: Sets the status of keyboard Insert mode.
: Loads a TSR program into memory.
: Loads a TSR program into upper memory, equivalent to HIINSTALL in DR DOS 5.0.
: Installs a TSR program after relocating the DOS data segment, similar to INSTALL.
: Adjusts PIC interrupt priorities so that a chosen IRQ receives highest priority.

KTemplate:NbndM

: Defines the keyboard layout configuration.
: Specifies the relocated keyboard buffer's address.
: Sets the maximum number of accessible drives.
: Similar to LASTDRIVE but also loads the Current Directory Structure into upper memory.
: Establishes DLL search path locations.
: Controls execution behavior for legacy applications.
: Determines the number of file locks allowed.
: Configures display of boot logos using the PTS-DOS boot manager.
: Sets parameters such as count, order, I/O address, and timeout for the LPT1 port.
: Functions like LPT1 configuration but applies to LPT2 device.
: Equivalent configuration for LPT3 device as with LPT1.
: Enables and configures LPT4 device similarly to other parallel ports.
: Defines wait time before elevating process priority when waiting.
: Manages memory allocation strategies within DOS operations.
: Specifies default memory allocation behavior in DOS environments.
: Assigns menu option selections.
: Defines menu color schemes (can be emulated via ECHO command in DR-DOS).
: Specifies default menu block (emulatable with TIMEOUT and SWITCH in DR-DOS).
: Defines individual menu blocks (emulatable using ECHO and SWITCH commands in DR-DOS).
: Enables operations involving multitrack disk handling.
: Continues CONFIG.SYS processing from a new file after loading specific drivers and setting the %NEWFILE% environment variable.

NTemplate:NbndQ

: Sets default No () response character in Yes/No/Resume prompts.
: Controls keyboard [[Num Lock|Template:Keypress]] state, turning it on or off.
: Executes commands conditionally based on the last error level, such as .
: Displays text and waits for a keypress, similar to DR-DOS’s and commands.
: Requires user confirmation upon encountering errors in CONFIG.SYS processing.
: Configures buffer sizes for printers connected via LPT1 through LPT3 ports.
: Enables conditional command execution on PC-compatible systems.
: Adjusts process scheduler priority settings.
: Sets priority levels for disk input/output tasks.
: Changes default printer port driver from LPT1 to either LPT3 or LPT4 devices.
: Determines whether DOS applications are permitted to run within the system environment.
: Loads the graphical user interface shell component.
: Allows conditional command execution on IBM PS/1-compatible hardware platforms.
: Supports conditional execution on IBM PS/2-compatible machines.
: Suppresses output directed to standard output (STDOUT).

RTemplate:NbndT

: Activates automatic system reboot upon encountering errors.
: Permits inclusion of comments within CONFIG.SYS files.
: Allocates a drive letter specifically for local block device drivers.
: Establishes the default Resume () character displayed in command prompts.
: Returns nested CONFIG.SYS processing control to the prior GOSUB or SWITCH point, optionally passing back a return code.
: Sets the size of real mode memory available to the system.
: Allows simultaneous loading of programs in CONFIG.SYS in the background, functioning similarly to CALL or INSTALL commands in DOS.
: Determines whether the first character of deleted files is saved in the FAT reserved area.
: Defines video mode settings under FreeDOS or specifies screen access methods for PTS-DOS.
: Controls the activation status of the keyboard’s Scroll Lock key.
: Establishes environment variables for the operating system.
: Loads the command interpreter shell into memory.
: Functions like SHELL but includes a size parameter to pre-allocate COMMAND.COM into HMA or UMBs, enhancing memory handling with third-party shells.
: Sets keyboard modifier key states such as Shift Lock, Num Lock, Scroll Lock, and Insert mode.
: Specifies whether files are closed during a Ctrl+Alt+Del reboot sequence.
: Bypasses POST procedures during system reboot.
, STACKSIZE, STACKSHIGH: Define configurations for hardware interrupt stacks and buffer placement across different DOS versions to optimize system reliability and memory utilization.
, SYSBOOT, SYSGEN, SYSLOAD: PTS-DOS-specific commands that manage boot sequence behavior, system memory arrangement, and loading from alternate disk sectors for flexible configuration options.
, SWITCH: Enables conditional execution and submenu constructs within CONFIG.SYS for more advanced script control (partially emulated in DR-DOS).
, SWAPPATH: OS/2 directives that designate locations for error logs and swap files to improve operational efficiency.
, SWITCHES: Establish default switch characters ('/' or '-') along with special flags that affect command parsing across various DOS systems.
, TRACEBUF: Controls global or local enabling of CONFIG.SYS single-step execution with adjustable log buffer sizes for debugging purposes in DR-DOS, PTS-DOS, and OS/2 platforms.

This segment highlights essential CONFIG.SYS commands crucial for configuring systems on multiple DOS variants—important knowledge for IT specialists maintaining legacy environments or embedded DOS systems aiming to optimize boot routines, memory allocation, and error management.

UTemplate:NbndZ

: Directs DOS to designate a particular segment as Upper Memory Block (UMB) space.
: Specifies which UMB server is utilized by the system.
: Defines address ranges allocated as UMB RAM areas.
: Toggles verification of disk writes on or off.
: Sets the DOS version string reported to applications.
: Configures VGA display parameters and status indicators.
: Indicates current video mode settings, comparable to FreeDOS’s SCREEN directive.
: Determines whether virtual DMA functionality is permitted.
: Controls disabling of processor Virtual Mode Extensions (VME).
: Sets up VxD driver parameters for Windows environments.
: Configures overall Windows system support features.
: Manages relocation settings for the Extended BIOS Data Area (XBDA).
: Implements conditional execution based on XT-compatible machine detection.
: Enables built-in Year 2000 compliance support mechanisms.
: Defines default affirmative response character used in Yes/No prompts.
: Configures tracking mechanisms for file deletions.

Issues

Although the system is capable of booting without CONFIG.SYS or AUTOEXEC.BAT, these configuration files are crucial for tailoring the operating system and loading necessary software components. If either file becomes corrupted or missing, troubleshooting is required.

In cases where CONFIG.SYS does not contain a SHELL directive, or if the file itself is absent or damaged, DOS defaults to searching for COMMAND.COM in the root directory of the boot drive. Earlier versions prior to 6.0 will fail to boot if COMMAND.COM is not located, whereas MS-DOS 6.0, PC DOS 6.1, and Novell DOS 7 and later will prompt the user to specify the path to a command interpreter. This recovery prompt also appears if the primary shell terminates unexpectedly or exits intentionally, providing an opportunity to replace the shell temporarily without rebooting.

The COMMAND.COM from MS-DOS 7.0 and onward is incompatible with DR-DOS systems, which commonly maintain COMMAND.COM in C:\ for dual-boot environments. Starting with DR-DOS 7.02, enforcement of SHELL directives during debugging modes such as skip, trace, or step prevents circumvention of these commands, enhancing system stability and recovery capabilities.

CONFIG.SYS file size restrictions vary among DOS variants: MS-DOS and PC DOS limit the file size to several kilobytes (up to 64 KB in later releases), whereas DR-DOS imposes no practical size constraint aside from the limits of the underlying file system. MS-DOS processes CONFIG.SYS by compiling it into a tokenized format that executes directives in a fixed sequence (device drivers before TSR programs). In contrast, DR-DOS interprets CONFIG.SYS line-by-line, granting granular control over loading order and enabling conditional execution based on hardware presence or error conditions—features that are particularly useful for conflict resolution and debugging.

Additionally, DR-DOS introduces the INSTALL directive, which allows integration of non-resident software within the CONFIG.SYS processing sequence for increased flexibility.

Regarding SHELL command line length limits, MS-DOS and PC DOS versions from 2.0 through 4.01 restrict this to 31 characters; subsequent releases expand this limit to 128 characters, while DR-DOS permits up to 255 characters. It should be noted that CONFIG.SYS directives do not support long filenames.

Dual booting DOS and Windows 9x

When Windows 95 is installed over an existing DOS or Windows environment, it renames CONFIG.SYS and AUTOEXEC.BAT to CONFIG.DOS and AUTOEXEC.DOS respectively. This renaming facilitates dual-boot functionality between Windows 9x and DOS by temporarily restoring these files to their original names when booting into DOS mode. Additionally, Windows 95 maintains backup copies named CONFIG.W40 and AUTOEXEC.W40.

In setups where Caldera DR-DOS versions 7.02 or 7.03 coexist with Windows 95, Windows retains its original CONFIG.SYS and AUTOEXEC.BAT filenames, whereas DR-DOS uses alternative startup files named DCONFIG.SYS and AUTODOS7.BAT.

OS/2 / Windows NT

OS/2 relies heavily on CONFIG.SYS for driver configuration and environment setup prior to launching its graphical user interface.

Within the OS/2 compatibility subsystem of Windows NT, the equivalent settings typically stored in CONFIG.SYS are instead managed through the system registry rather than traditional configuration files.

A substantial number of undocumented CONFIG.SYS commands exist specifically for OS/2, reflecting its intricate configuration requirements.

CONFIG.SYS continues to be utilized by OS/2 derivatives such as eComStation and ArcaOS.

External links

Information on AUTOEXEC.BAT and CONFIG.SYS at Computer Hope
Overview of Windows 98 / MS-DOS 7.10 CONFIG.SYS directives (archived)
Caldera’s CONFIG.SYS Command Reference (archived) – summary of DR-DOS 7 directives
FreeDOS CONFIG.SYS directives explained
PTS-DOS 2000 Pro User Manual including details on CONFIG.SYS directives
Unofficial German PTS-DOS FAQ (2004) featuring additional CONFIG.SYS directive information