QUIET (CONFIG.SYS directive)

CONFIG.SYS
Company type	Configuration file
Industry	Computer software
Founded	1983
Headquarters	N/A
Products	Configuration for DOS and OS/2 operating systems

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

CONFIG.SYS serves as the chief configuration file for both DOS and OS/2 operating systems. This plain text file, written in ASCII, holds setup instructions accessible to users, which the operating system's DOS BIOS—commonly found in IBMBIO.COM or IO.SYS—interprets during the startup process. CONFIG.SYS made its debut with DOS version 2.0.

Usage

The directives within CONFIG.SYS tailor DOS to manage hardware devices, software applications, and memory allocation. Once CONFIG.SYS has been processed, DOS initiates the command interpreter specified by the SHELL directive or defaults to COMMAND.COM, which subsequently executes AUTOEXEC.BAT.

This file primarily consists of name=value pairs that either adjust configurable parameters or load files like device drivers and terminate-and-stay-resident programs (TSRs). Within DOS environments, CONFIG.SYS is located in the boot drive’s root directory.

Certain DOS variants check for alternative filenames that override CONFIG.SYS:

- Advanced editions of Concurrent DOS 386, Concurrent DOS XM, Multiuser DOS, and REAL/32 utilize CCONFIG.SYS or CCONFIG.INI instead, with additional configuration stored in CCONFIG.BIN, which is managed through CONFIG.EXE. - In DR DOS versions 3.31 and later, DCONFIG.SYS takes priority, facilitating multi-boot configurations and disk compression support. - OpenDOS 7.01 and DR-DOS releases 7.02 and beyond also accept ODCONFIG.SYS or DRCONFIG.SYS as configuration files. - From DR-DOS 6.0 onward, the default file extension can be altered using SYS /DR:ext, allowing multiple system file sets to coexist and be chosen via boot loaders such as LOADER. - The SHELL command supports specifying alternate AUTOEXEC.BAT files using /P[:filename.ext], with COMMAND.COM permitting extensions other than .BAT. - Additionally, DR-DOS 6.0+ introduces CHAIN=filespec, enabling continuation of configuration processing from another file, optionally targeting a specific label.

Other operating systems employ similar alternate configuration files: FreeDOS uses FDCONFIG.SYS, RxDOS relies on RXCONFIG.SYS, and PTS-DOS implements CONFIG.PTS.

In Windows 95 and 98—which are based on DOS—both CONFIG.SYS and AUTOEXEC.BAT exist but are generally left empty. Windows Me does not process CONFIG.SYS during startup; instead, it retrieves environment variables directly from the Windows Registry.

For FlexOS, CONFIG.SYS is a binary configuration file that specifies resource managers and device drivers to be loaded at boot time.

Example

Below is a sample CONFIG.SYS file for MS-DOS version 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 to serve as jump points for , , , and commands.
: Functions like , but also permits inline comments following other directives. (Note that under MS-DOS/PC DOS, inline comments enclosed in double quotes are not disregarded.)
: Provides an alternative syntax for inline comments at the start of a line.
: Prompts a Yes/No confirmation dialog with an optional message before executing subsequent directives. (FreeDOS enhances this with conditional boot menu support.) Starting with DOS 6.0+, similar functionality exists by appending after commands.
: Forces unconditional execution of the following directive.

ATemplate:NbndC

: Determines whether programs may terminate upon encountering errors.
: Sets drives to retain file access timestamps within FAT reserved sectors.
: Enables conditional execution on AT-compatible systems.
: Manages boot loading processes.
: Adjusts the level of detail for error messages.
: Alters the default serial driver assigned to the AUX device.
: Restricts access to character devices outside the phantom \DEV directory.
: Loads the fundamental device driver into memory.
: Produces a brief beep even if sound notifications are disabled.
: Defines which operating system will boot next.
: Enables or disables extended checking for Ctrl+C interrupts.
: Specifies how many disk buffers should be allocated.
: Similar to BUFFERS, but places buffers in HMA or UMB areas.
, , (Embedded DOS 6-XL exclusive): Controls allocation and timing of cache blocks.
: Loads programs listed in CONFIG.SYS and pauses processing until completion.
: Sets the Caps Lock key status on the keyboard.
, (PTS-DOS specific): Configures CD-ROM driver parameters.
: Continues processing CONFIG.SYS from a new file or label.
, , and additional PTS-DOS directives adjust system behavior and visual output.

COM Ports

Directives such as COM1 through COM4 (introduced in DR-DOS 7.02 and later) specify the number, sequence, I/O addresses, and timeout values for serial port devices.

COMMENT

, introduced in DOS 4.0, allows redefining inline comment characters or causes lines to be ignored during processing.

COUNTRY

Activates internationalization features in DOS versions 3.0 and above as well as OS/2 environments.

CPU-specific directives

Conditional directives based on CPU models (8088, 8086, 286, 386, etc.) are primarily supported by PTS-DOS and DR-DOS variants.

This concise summary emphasizes key CONFIG.SYS directives relevant to business users managing legacy DOS systems, facilitating effective device configuration and boot management critical for enterprises relying on these platforms.

DTemplate:NbndF

: Adjusts relocation settings for drive descriptor tables.
: Defines memory segment address used for multi-sector disk data deblocking.
: Activates internal debugging capabilities.
: Controls boot management functions.
: Loads a device driver into conventional memory.
: Loads a device driver into upper memory blocks (equivalent to in DRDOS 5.0).
: Sets country and codepage information for keyboard, screen, and printer devices.
: Configures cache sizes for memory management.
: Specifies compatibility mode for floppy disks.
: Defines display font settings.
: Determines loading of DOS into high memory and/or utilization of upper memory areas.
: Loads DOS tables such as BUFFERS, FCBS, FILES, LASTDRIVE, STACKS into upper memory regions.
: Provides an alternative directory path for DOS files.

: Specifies search directories for data files.
: Configures physical parameters for disk drives.
: Sets parameters for drives not otherwise recognized by the system.
: See .
: Enables PDUMP.nnn error logging and assigns the target drive.
: Outputs a message on the display screen.
: Outputs messages including ANSI escape sequences for formatting.
: Determines whether extra checks occur when launching programs.
: Specifies the error or return code to be assumed next in sequence.
: Controls the A20 gate state when starting an application.
: Terminates CONFIG.SYS processing before reaching the end of the file (with exceptions such as SWITCHES and SHELL).
: Defines hash table size used to speed up file open operations, differing from MS-DOS/PC DOS FASTOPEN functionality.
: Number of cached File Control Blocks (FCBs) allowed open simultaneously (shares buffer space with FILES under DR-DOS).
: Same as FCBS but loads FCBs into upper memory areas.
: Boot management directive.
: Specifies maximum number of files open at once.
: Same as FILES but loads file handles into upper memory blocks.
: Executes specified CONFIG.SYS subsections (refer to IGNORE).

GTemplate:NbndI

: Waits for a key press or timeout, then assigns 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, returning afterward to the prior point.
: Refer to , , or for additional details.
: Consult for further information.
: See for more context.
: Consult or for related commands.
: Refer to or for additional references.
: See for more details.
: Loads a TSR program into memory following DOS data segment relocation; compare with INSTCDEX.
: Refer to , , or for related functions.
: See for further explanation.
: Consult or for related usage.
: Activates console and command line history buffer with enhanced search capabilities.
: Defines the HMA segment address.
: Sets HLT power-saving mode configuration.
: Enables scanning of the boot sector for viruses.
: Loads installable file systems into memory.
: Prevents execution of designated CONFIG.SYS subsections; see also .
: Permits specified programs to operate at CPU ring 2, allowing direct hardware I/O access.
: Incorporates directives from an alternate menu block (can be emulated via GOSUB/RETURN in DR-DOS).
: Sets the status of the 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 TSR program after DOS data segment relocation; compare with INSTCDEX.
: Rotates PIC interrupt priorities, assigning highest priority to a specified IRQ number.

KTemplate:NbndM

: Defines the keyboard layout configuration.
: Provides the address of the relocated keyboard buffer.
: Specifies the maximum number of accessible drives.
: Similar to LASTDRIVE but loads the Current Directory Structure into upper memory.
: Lists search paths used for locating DLLs.
: Manages loading of legacy applications.
: Indicates the number of file locks allowed.
: Configures boot logo display and startup messages using PTS-DOS boot manager.
: Specifies count, order, I/O address, and timeout settings for LPT1 device.
: Configures LPT2 device similarly with respective parameters.
: Sets up LPT3 device with analogous settings.
: Enables and configures LPT4 device parameters.
: Defines wait duration before process priority is increased.
: Determines memory allocation strategy settings.
: Sets default DOS memory allocation method.
: Specifies menu options available to users.
: Defines menu color schemes (can be emulated in DR-DOS).
: Establishes default menu block (emulatable within DR-DOS).
: Creates a menu block (also emulatable in DR-DOS).
: Enables multitrack disk operations functionality.
: Continues processing CONFIG.SYS from a new file after loading device drivers and setting %NEWFILE% environment variable.

NTemplate:NbndQ

: Sets default negative response character () in Yes/No/Resume prompts.
: Controls status of keyboard Num Lock key on startup.
: Executes commands conditionally based on last error code, e.g., .
: Displays text and waits for user key press, similar to DR-DOS’s and .
: Requires user acknowledgment when errors occur during CONFIG.SYS processing.
: Configures buffer sizes for LPT ports output operations.
: Executes conditionally on PC-compatible machines only.
: Sets process scheduler priority level.
: Defines disk I/O priority settings.
: Changes default printer driver from LPT1 to LPT3 or LPT4 as specified.
: Indicates whether DOS programs are permitted to run or not.
: Loads a user interface module during boot-up sequence.
: Executes conditionally on IBM PS/1-compatible hardware platforms only.
: Executes conditionally on IBM PS/2-compatible hardware platforms only.
: Suppresses output sent to STDOUT.

RTemplate:NbndT

: Activates automatic system reboot upon encountering errors.
: Permits inclusion of comments within CONFIG.SYS (not recognized by PTS-DOS).
: Allocates drive letters reserved for local block device drivers.
: Defines the default Resume () character used in Yes/No/Resume prompts.
: Returns control from nested CONFIG.SYS processing to the prior GOSUB or SWITCH location, optionally passing a return code.
: Sets the size of real mode memory available.
: Allows concurrent loading of programs within CONFIG.SYS, functioning similarly to CALL or INSTALL commands in DOS.
: Determines whether the initial character of deleted files is stored in the FAT reserved area.
: Specifies video mode settings (FreeDOS) or screen access methods (PTS-DOS).
: Controls the status of the keyboard Scroll Lock key.
: Establishes environment variables.
: Loads the command interpreter shell.
: Functions like SHELL but includes a size parameter to relocate COMMAND.COM into HMA or UMBs, optimizing memory usage especially with third-party shells.
: Defines keyboard modifier states such as Shift Lock, Num Lock, Scroll Lock, and Insert mode.
: Determines if files close automatically when Ctrl+Alt+Del is pressed.
: Specifies whether POST is skipped during reboot.
, STACKSIZE, STACKSHIGH, STACK, THREADS, etc.: Configure various memory stack sizes and thread management across DOS versions and OS/2 for interrupt handling and multitasking.
, SYSBOOT, SYSGEN, SYSLOAD, SYSTOUMB (PTS-DOS): Manage boot procedures, system memory allocation, and loading addresses to enhance performance.
, SWITCH, SWITCHES (DOS variants): Enable conditional processing within CONFIG.SYS using labels and options for adaptable system configuration.
, SWAPPATH (OS/2): Direct error log locations and swap file paths to maintain system stability.
, TMPEXT (Various DOS): Define system-wide defaults such as switch characters ('/' or '-') and temporary file extensions for consistent environment behavior.
, TRACE, TRACEBUF (DR-DOS, PTS-DOS, OS/2): Set timeouts for command processing steps and activate detailed logging to facilitate troubleshooting.
, SXFAKEHWFPU (OS/2): Provide advanced error logging and apply fixes for hardware floating point unit bugs to improve system reliability.

UTemplate:NbndZ

: Designates a specific memory segment for use as Upper Memory Block (UMB).
: Selects the UMB server implementation employed by DOS.
: Defines address ranges allocated as UMB RAM.
: Enables or disables verification of disk writes.
: Sets the DOS version number presented to applications.
: Configures VGA display settings status.
: Specifies the active video mode.
: Determines whether virtual DMA is permitted.
: Controls deactivation of processor Virtual Mode Extensions (VME).
: Configures VxD driver parameters for Windows environments.
: Sets up system support tailored for Windows operation.
: Manages relocation of the Extended BIOS Data Area (XBDA).
: Enables conditional execution on XT-compatible machines.
: Activates built-in Year 2000 compatibility support.
: Defines the default 'Yes' character used in prompt responses.
: Configures tracking of file deletions.

Issues

Although it is possible for the system to boot without CONFIG.SYS or AUTOEXEC.BAT files, these are crucial for comprehensive operating system customization and meeting software prerequisites. If these files become corrupted or damaged, troubleshooting becomes necessary.

In cases where CONFIG.SYS lacks a SHELL directive—or if it is missing or corrupted—DOS attempts to locate COMMAND.COM in the root directory of the boot drive. Versions prior to 6.0 will fail to boot if COMMAND.COM cannot be found. Starting with MS-DOS 6.0, PC DOS 6.1, Novell DOS 7+, and later editions, if COMMAND.COM is absent or fails to load, users are prompted to specify a command processor path. This prompt also facilitates limited runtime replacement of the shell without requiring a reboot.

COMMAND.COM from MS-DOS version 7.0 onward is incompatible with DR-DOS systems. This incompatibility impacts dual-boot configurations where DR-DOS versions 7.02 and above no longer allow bypassing SHELL directives during skip, trace, or step modes. Some subsequent patches reintroduced skip capabilities to enable recovery from invalid SHELL arguments. When skipping CONFIG.SYS processing without locating a SHELL directive, users are prompted to enter a valid shell filename before COMMAND.COM loads.

CONFIG.SYS file size under MS-DOS/PC DOS is constrained to a few kilobytes—up to approximately 64 KB in later versions—whereas DR-DOS imposes no explicit size limit beyond file system restrictions. MS-DOS processes CONFIG.SYS by compiling it into a tokenized structure held in memory that executes directives sequentially—loading device drivers prior to TSRs. Conversely, DR-DOS interprets CONFIG.SYS line-by-line during execution, offering greater flexibility in load order via DEVICE and INSTALL commands. This approach aids in resolving conflicts and simplifies debugging.

The line-by-line interpretation in DR-DOS supports conditional execution triggered by processor type detection, key presses, error conditions, or return codes. This enhances customization possibilities and user interaction during startup. The INSTALL directive allows non-resident programs to be loaded dynamically during CONFIG.SYS processing, integrating temporary utilities into system configuration.

In MS-DOS/PC DOS versions from 2.0 through 4.01, the length of the SHELL command line was limited to a maximum of 31 characters. Later versions expanded this limit up 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 a pre-existing DOS or Windows environment, it renames the CONFIG.SYS and AUTOEXEC.BAT files to CONFIG.DOS and AUTOEXEC.DOS respectively, enabling a dual boot setup between Windows 9x and DOS. During a DOS boot, these files are temporarily restored to their original filenames. Additionally, Windows 95 creates backup copies of these files as CONFIG.W40 and AUTOEXEC.W40.

In configurations where Caldera DR-DOS versions 7.02 or 7.03 coexist with Windows 95, the original CONFIG.SYS and AUTOEXEC.BAT files used by Windows remain intact. Instead, DR-DOS employs alternative startup files named DCONFIG.SYS and AUTODOS7.BAT.

OS/2 and Windows NT

The OS/2 operating system makes extensive use of CONFIG.SYS to set up its environment, load drivers, and configure system parameters before the graphical user interface starts.

Within the OS/2 subsystem included in Windows NT, CONFIG.SYS is presented to OS/2 applications; however, this file is actually maintained within the system registry rather than as a physical file.

Numerous CONFIG.SYS commands utilized by OS/2 lack comprehensive documentation or remain partially undocumented.

CONFIG.SYS continues to be an important configuration file in OS/2-based systems such as eComStation and ArcaOS.

External links

Information on AUTOEXEC.BAT and CONFIG.SYS – Computer Hope (2017)
Overview of Windows 98 / MS-DOS 7.10 CONFIG.SYS directives – Microsoft Support (archived)
CONFIG.SYS Command Reference – Caldera (1998) (partial DR-DOS 7 directive list)
FreeDOS CONFIG.SYS directive descriptions
PTS-DOS 2000 Pro User Manual (includes partial PTS-DOS CONFIG.SYS directives)
Unofficial German PTS-DOS FAQ (2004) (provides additional CONFIG.SYS directives)