SUPPRESSPOPUPS (CONFIG.SYS directive)
| Company type | Configuration file |
|---|---|
| Industry | Computer software / Operating systems |
| Founded | 1983 |
| Headquarters | N/A |
| Products | Configuration for DOS and OS/2 startup |
CONFIG.SYS serves as the central configuration file for DOS and OS/2 operating systems. This plain ASCII text file holds setup instructions accessible to users, which the operating system's DOS BIOS interprets during the startup sequence. CONFIG.SYS made its debut with DOS version 2.0.
Usage
The directives within CONFIG.SYS are responsible for configuring DOS to manage devices, applications, and memory allocation. Once CONFIG.SYS has been processed, DOS initiates the command interpreter specified in the SHELL directive; if none is provided, it defaults to COMMAND.COM, which subsequently executes AUTOEXEC.BAT.
Primarily, the file contains name=value pairs that set adjustable parameters or load device drivers and terminate-and-stay-resident programs (TSRs) into memory. CONFIG.SYS is located in the root directory of the system’s boot drive.
Certain DOS variants check for alternative configuration filenames that take precedence over CONFIG.SYS:
- Advanced editions of Concurrent DOS 386, Concurrent DOS XM, Multiuser DOS, System Manager, and REAL/32 utilize CCONFIG.SYS or CCONFIG.INI instead, with supplementary settings stored in CCONFIG.BIN, typically modified via CONFIG.EXE.
- Versions of DR DOS starting from 3.31, including PalmDOS 1.0 and Novell DOS 7, prioritize DCONFIG.SYS, facilitating multi-boot environments and disk compression features.
- OpenDOS 7.01 and DR-OpenDOS 7.02 also search for ODCONFIG.SYS or DRCONFIG.SYS as alternatives.
- From DR DOS 6.0 onward, users can alter default file extensions using SYS /DR:ext, enabling multiple concurrent system file sets selectable through boot loaders such as LOADER.
- Enhanced SHELL commands permit specifying alternative AUTOEXEC.BAT files with extensions other than ".BAT".
- The CHAIN=filespec command allows continuation of processing in another file, supporting label usage in DR-DOS 7.02 and later.
- Starting with DR-DOS 7.03, SYS /A copies CONFIG.SYS and AUTOEXEC.BAT alongside system files.
Other operating systems use similar configuration files: FDCONFIG.SYS for FreeDOS, RXCONFIG.SYS for RxDOS, and CONFIG.PTS for PTS-DOS.
In Windows 95 and 98, CONFIG.SYS and AUTOEXEC.BAT are present in the root of the boot drive but generally remain empty. Windows Me does not process CONFIG.SYS during startup; instead, environment variables are loaded from the Windows Registry.
On the FlexOS platform, CONFIG.SYS is a binary file that specifies resource managers and device drivers to be loaded at boot time.
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>
:;*?!
- Defines jump points within CONFIG.SYS labels usable by , , , and commands.
- Functions like , but additionally allows inline comments following other instructions. (In MS-DOS/PC DOS, inline comments inside double quotes are not ignored.)
- Used to start inline comments along with ;.
- Prompts a Yes/No confirmation before executing subsequent CONFIG.SYS commands. (FreeDOS does not support custom messages but allows conditional execution via boot menus.) DOS version 6.0 and later offers a similar feature using a trailing after commands.
- Forces unconditional execution of the next CONFIG.SYS command.
ATemplate:NbndC
- Determines whether programs may be terminated upon encountering errors.
- Defines which drives record file access timestamps within FAT file systems.
- Allows conditional command execution on AT-compatible hardware.
- Manages boot loading operations.
- Adjusts the level of detail in error message output.
- Changes the default serial port driver (from COM1: to COM4:) for the AUX device.
- Restricts access to character devices outside the phantom \DEV directory.
- Loads fundamental device drivers into memory.
- Produces a brief beep even if audible alerts are disabled.
- Specifies the next operating system designated for booting.
- Enables or disables extended Ctrl+C detection.
- Sets the number of disk buffers allocated in memory.
- Similar to BUFFERS but loads buffers into HMA or UMB areas.
- , ,
- Configures cache block size, timeout before release, and timing for cache flushing.
- Loads programs listed in CONFIG.SYS and pauses processing until they complete.
- Sets the Caps Lock key status on the keyboard.
- ,
- Defines CD-ROM driver name and the number of buffers allocated for it.
- Continues processing CONFIG.SYS from a new file or label.
- , , , and other hardware/configuration directives specify clock type, screen clearing, OEM codepages, and more, mainly targeting OS/2 or specific DOS variants.
- , ...,
- Define COM port configurations (applicable from DR-DOS 7.02 onwards).
- , Used to insert inline comments or ignore lines, varying by DOS version.
- , Enables internationalization support across various DOS versions.
- CPU-related directives (CPU88, CPU286+, CPU386, etc.) conditionally execute commands based on detected CPU type (PTS-DOS and DR-DOS).
DTemplate:NbndF
- Configures relocation settings for drive descriptor tables.
- Specifies memory segment address used for multi-sector disk data deblocking.
- Activates internal debugger support features.
- Manages boot loading processes.
- Loads device drivers into conventional memory areas.
- Loads device drivers into upper memory blocks (similar to in DRDOS 5.0).
- Sets country and codepage information for keyboard, screen, and printer devices.
- Defines cache memory sizes for system optimization.
- Selects floppy disk compatibility mode settings.
- Specifies display font characteristics.
- Controls loading of DOS into high or upper memory regions, similar to in DRDOS 5.0.
- Loads DOS internal tables (BUFFERS, FCBS, FILES) into upper memory space.
- Specifies an alternate directory path for DOS system files.
- Establishes search paths for data files used by the system.
- Defines physical parameters of disk drives connected to the system.
- Sets parameters for drives that are not recognized automatically by DOS.
- See .
- Enables PDUMP.nnn error logging and specifies target drive location for logs.
- Displays text messages on screen output devices.
- Displays messages incorporating ANSI escape sequences for enhanced formatting.
- Adds extra verification steps when launching programs.
- Assigns assumed error or return codes for subsequent commands executed by the system.
- Sets the state of the A20 address line when starting a program to control memory access above 1MB.
- Terminates CONFIG.SYS processing early except for SWITCHES and SHELL directives that must still be processed.
- Defines hash table size used to accelerate file open operations, differing from MS-DOS FASTOPEN driver behavior.
- Sets number of cached File Control Blocks (FCBs) that can be open simultaneously (shares buffer space with FILES under DR-DOS).
- Functions like FCBS but loads FCBs into upper memory areas instead of conventional memory.
- Boot management utility directive.
- Specifies maximum number of files that can be open at once by the system.
- Similar to FILES but loads file handles into upper memory blocks rather than conventional memory.
- Includes execution of designated CONFIG.SYS subsections as specified by IGNORE directive.
GTemplate:NbndI
- Waits for a keystroke or timeout, then assigns the error level to the corresponding ASCII value (or 1024 if timed out).
- Resumes processing of CONFIG.SYS at the indicated label.
- Continues nested CONFIG.SYS execution at a specified label, returning afterward to the prior point.
- Refer to , , or for additional details.
- See also .
- Consult .
- Refer to or for further information.
- See or for more context.
- Consult .
- Loads a TSR program into memory similarly to , but after DOS relocates its data segment.
- See , , or for related commands.
- Refer to .
- See or for additional guidance.
- Activates console and command-line history buffers with enhanced pattern search capabilities.
- Specifies the address of the High Memory Area (HMA) segment.
- Configures the energy-saving mode using HLT instruction.
- Determines whether to perform a boot sector virus check during system startup.
- Loads installable file system drivers.
- Prevents execution of designated CONFIG.SYS subsections.
- Permits specific programs to operate at CPU ring 2, allowing direct hardware I/O access.
- Incorporates directives from another menu section (implemented via GOSUB/RETURN in DR-DOS).
- Sets the status of keyboard Insert mode.
- Installs a TSR program into memory.
- Loads TSR programs into upper memory areas (similar to HIINSTALL in DR DOS 5.0).
- Installs TSR after relocation of DOS data segment.
- Adjusts PIC interrupt priorities to prioritize a specified IRQ line.
KTemplate:NbndM
- Defines the keyboard layout configuration.
- Sets the relocated address of the keyboard buffer.
- Establishes the maximum number of accessible drives.
- Similar to LASTDRIVE but additionally loads Current Directory Structure into upper memory.
- Specifies search paths for DLL files.
- Manages compatibility loading for legacy applications.
- Determines the number of allowable file locks.
- Controls display of boot logos when using PTS-DOS boot manager.
- Configures count, sequence, I/O port address, and timeout settings for LPT1 device.
- Applies identical settings as LPT1 for LPT2 device.
- Applies identical settings as LPT1 for LPT3 device.
- Enables and configures LPT4 device in a similar manner.
- Defines delay before elevating process priority during execution.
- Sets strategy for memory allocation management.
- Specifies default DOS memory allocation policy.
- Defines available menu options.
- Configures color schemes for menus (emulatable under DR-DOS).
- Specifies default menu block (emulation supported in DR-DOS).
- Defines individual menu blocks (emulatable within DR-DOS).
- Enables multitrack disk access operations.
- Continues CONFIG.SYS processing in a new file after loading a device driver and setting %NEWFILE% environment variable.
NTemplate:NbndQ
- Sets default response character to No () in Yes/No/Resume prompts.
- Toggles keyboard [[Num Lock|Template:Keypress]] state on or off at startup.
- Enables conditional execution based on previous error level, e.g., .
- Displays text and waits for a keypress, similar to and commands in DR-DOS environments.
- Requires user acknowledgment of errors during CONFIG.SYS processing.
- Configures buffer sizes for LPT ports.
- Enables conditional execution on PC-compatible systems.
- Sets process scheduling priority levels.
- Adjusts priority specifically for disk I/O intensive applications.
- Changes default printer device driver assignment among LPT1 through LPT4 ports.
- Restricts execution of DOS applications under certain conditions.
- Loads a user interface shell environment.
- Enables conditional execution on IBM PS/1-compatible systems.
- Enables conditional execution on IBM PS/2-compatible systems.
- Mutes output directed to STDOUT.
RTemplate:NbndT
- Activates automatic system reboot upon encountering errors.
- Permits inclusion of comments within CONFIG.SYS files.
- Allocates drive letters reserved by local block device drivers.
- Defines the default character for Resume () prompts.
- Allows nested CONFIG.SYS processing to return to the previous GOSUB or SWITCH statement, optionally with a return code.
- Sets the size of real mode memory.
- Enables simultaneous loading of programs in CONFIG.SYS, functioning similarly to CALL or INSTALL commands found in DOS variants.
- Saves the initial character of deleted files in a reserved FAT area.
- Determines video mode settings (FreeDOS) or screen access methods (PTS-DOS).
- Controls the on/off state of the keyboard Scroll Lock key.
- Assigns environment variable values.
- Loads the command interpreter shell program.
- Functions like SHELL but includes pre-allocation size parameters to load COMMAND.COM into HMA or UMBs, enhancing memory efficiency with third-party shells.
- Sets keyboard modifier keys such as Shift Lock, Num Lock, Scroll Lock, and Insert mode.
- Defines file closure behavior triggered by Ctrl+Alt+Del key combination.
- Skips Power-On Self-Test (POST) during system reboot sequences.
- , STACKSIZE, STACKSHIGH
- Configure hardware interrupt stack sizes and buffer locations across various DOS platforms with differing levels of support.
- , SYSBOOT, SYSGEN, SYSLOAD
- Directives exclusive to PTS-DOS for managing boot processes and system memory configurations.
- Establishes submenu blocks available in DOS 6.0 and later versions; unsupported by DR-DOS or FreeDOS but can be simulated through command utilities.
- , SWAPPATH, THREADS, TIMESLICE
- OS/2-specific commands that handle error logging, swap file path definitions, threading control, and CPU time slice scheduling.
- , SWITCHES
- Conditional processing commands implemented in DR DOS and Novell DOS with limited functionality on other systems.
- , TMPEXT
- Defines system switch characters and temporary file extensions supported across various DOS versions.
- , TRACEBUF
- Enables or configures single-step execution logging within CONFIG.SYS under DR-DOS, PTS-DOS, FreeDOS, and OS/2 environments with varying capabilities.
- , SXFAKEHWFPU
- OS/2-specific directives for error logging and activation of floating-point unit (FPU) bug fixes.
This segment details sophisticated CONFIG.SYS directives predominantly utilized in DR-DOS, PTS-DOS, OS/2, and related operating systems. These commands facilitate system customization, enhance memory management strategies, regulate device driver behavior, and oversee boot procedures—essential for enterprises seeking to adapt legacy platforms to specialized operational requirements.
UTemplate:NbndZ
- Assigns a particular memory segment for use as Upper Memory Block (UMB) space under DOS management.
- Specifies which UMB server is employed by the system.
- Defines address ranges designated as Upper Memory Block RAM areas.
- Toggles disk write verification on or off.
- Sets the DOS version string reported to running applications.
- Controls VGA display status settings.
- Indicates the active video mode configuration.
- Determines whether virtual DMA is enabled or disabled.
- Configures whether processor Virtual Mode Extensions should be turned off.
- Manages VxD driver settings for Windows environments.
- Configures overall system support tailored for Windows operation.
- Adjusts relocation parameters for the Extended BIOS Data Area (EBDA).
- Enables conditional execution exclusively on XT-compatible hardware platforms.
- Configures integrated Year 2000 compliance support features.
- Specifies the default affirmative character used in user prompts.
- Manages 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 comprehensive operating system customization and meeting software prerequisites. Any damage or corruption to these files necessitates diagnostic measures.
In cases where CONFIG.SYS does not include a SHELL command (or if the file is missing or corrupted), DOS attempts to locate COMMAND.COM in the root directory of the boot drive. Earlier versions prior to 6.0 will fail if COMMAND.COM is absent, whereas MS-DOS 6.0, PC DOS 6.1, and Novell DOS 7 and later versions display a prompt requesting the path to a command interpreter. This recovery prompt also occurs if the main command processor terminates unexpectedly or exits intentionally, offering a limited runtime shell alternative without requiring a system reboot.
For systems running MS-DOS 7.0 and above, COMMAND.COM is not compatible with DR-DOS, although it is commonly found in the root of drive C: within dual-boot environments. DR-DOS versions 7.02 and later prevent bypassing SHELL directives during skip, trace, or step modes to improve system reliability. However, certain subsequent releases reintroduced skip functionality to recover from invalid SHELL parameters. When no valid SHELL directive is detected during skip mode, users are prompted to specify an appropriate shell before COMMAND.COM loads.
The maximum size allowed for CONFIG.SYS files varies depending on the operating system: MS-DOS and PC DOS impose limits up to 64 KB, while DR-DOS does not enforce a practical size restriction, processing directives sequentially rather than compiling them all at once. This approach provides fine-grained control over the sequence of driver and TSR loading as well as conditional execution based on hardware detection or error handling—advantages that assist in resolving conflicts or incorporating debugging tools.
Regarding SHELL command line length restrictions, MS-DOS and PC DOS versions from 2.0 through 4.01 restricted this to 31 characters; later editions expanded this limit to 128 characters. DR-DOS supports even longer lines, up to 255 characters. It is important to note that CONFIG.SYS directives do not accommodate long filenames.
Dual booting DOS and Windows 9x
During installation of Windows 95 over an existing DOS or Windows environment, the original CONFIG.SYS and AUTOEXEC.BAT files are renamed to CONFIG.DOS and AUTOEXEC.DOS respectively, enabling dual boot functionality between Windows 9x and DOS. Upon booting into DOS mode, these renamed files are temporarily restored to their original filenames. Additionally, Windows 95 creates backup versions labeled CONFIG.W40 and AUTOEXEC.W40.
When Caldera DR-DOS versions 7.02 or 7.03 coexist with Windows 95, the Windows configuration files CONFIG.SYS and AUTOEXEC.BAT remain unaltered. Instead, DR-DOS utilizes separate startup configuration files named DCONFIG.SYS and AUTODOS7.BAT.
OS/2 / Windows NT
OS/2 depends extensively on CONFIG.SYS for setting up device drivers and environment variables prior to launching its graphical user interface.
Within the OS/2 subsystem included in Windows NT, settings traditionally stored in CONFIG.SYS for OS/2 applications are maintained within the system registry rather than conventional configuration files.
The OS/2 operating system contains numerous undocumented CONFIG.SYS commands that reflect its intricate configuration requirements.
CONFIG.SYS continues to be a fundamental component in OS/2-based systems such as eComStation and ArcaOS.
See also
- IBMBIO.COM / IO.SYS
- IBMDOS.COM / MSDOS.SYS
- CONFIG (environment variable)
- AUTOEXEC.BAT
- COMMAND.COM
- List of DOS commands
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 description
- PTS-DOS 2000 Pro User Manual including CONFIG.SYS directives (archived)
- Unofficial German-language PTS-DOS FAQ (archived) – additional CONFIG.SYS commands