DUMPPROCESS (CONFIG.SYS directive)
| Company type | Configuration file |
|---|---|
| Industry | Computer software |
| Founded | 1983 |
| Headquarters | N/A , N/A |
| Products | Configuration for DOS and OS/2 operating systems |
CONFIG.SYS serves as the main configuration file utilized by the DOS and OS/2 operating systems. This plain text file, written in ASCII, contains setup commands that the operating system's DOS BIOS—usually located in IBMBIO.COM or IO.SYS—interprets during system startup. CONFIG.SYS was first introduced with DOS version 2.0.
Usage
The instructions within CONFIG.SYS tailor DOS to manage hardware devices, applications, and memory allocation. Once CONFIG.SYS has been processed, DOS initiates the command interpreter specified by the SHELL directive; if none is provided, it defaults to COMMAND.COM, which then executes AUTOEXEC.BAT.
Typically, CONFIG.SYS holds name=value pairs that set configurable options or load essential files such as device drivers and terminate-and-stay-resident programs (TSRs). This file is located in the boot drive’s root directory.
Certain DOS versions check for alternate configuration filenames before defaulting to CONFIG.SYS:
- Advanced editions of Concurrent DOS 386, Concurrent DOS XM, Multiuser DOS, and REAL/32 prioritize CCONFIG.SYS or CCONFIG.INI (Multiuser DOS) and MCONFIG.SYS (REAL/32). These support extended settings stored in binary files like CCONFIG.BIN, which are generally modified using CONFIG.EXE.
- In DR DOS 3.31, PalmDOS 1.0, and Novell-related distributions, DCONFIG.SYS is preferred, commonly employed alongside disk compression utilities or multi-boot configurations. OpenDOS 7.01 and DR-OpenDOS 7.02 also recognize ODCONFIG.SYS or DRCONFIG.SYS. The command SYS /DR:ext enables customization of default file extensions to facilitate multiple concurrent system file sets.
- Starting with DR-DOS 6.0, enhanced SHELL directives allow specifying alternative AUTOEXEC.BAT files and support additional file extensions—a functionality also available in 4DOS. The CHAIN=filespec command permits continuation of processing from another configuration file, optionally directing execution to specific labels in DR-DOS 7.02 and later.
- From DR-DOS 7.03 onward, the SYS /A option copies CONFIG.SYS and AUTOEXEC.BAT alongside other system files.
Other DOS variants offer similar configuration mechanisms: FDCONFIG.SYS for FreeDOS, RXCONFIG.SYS in RxDOS version 7.24 and above, and CONFIG.PTS within PTS-DOS.
In Windows editions built on DOS (Windows 95 and 98), CONFIG.SYS and AUTOEXEC.BAT files remain present but are usually left empty. Windows Me no longer processes CONFIG.SYS during startup; instead, it retrieves environment variables directly from the Windows Registry at:
- HKLM\System\CurrentControlSet\Control\SessionManager\Environment
For FlexOS, CONFIG.SYS is a binary-formatted file that specifies resource managers and device drivers loaded at boot time.
Example
Sample CONFIG.SYS configuration 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 that serve as jump points for , , , , and commands.
- Functions like , additionally enabling inline comments after directives. (Note that MS-DOS/PC DOS does not ignore inline comments enclosed in double quotes.)
- Used to start inline comments alongside the ; directive.
- Prompts with a Yes/No confirmation before executing subsequent CONFIG.SYS commands.[1] (While FreeDOS supports optional conditions through boot menus, it does not offer optional messages.) From DOS version 6.0 onward, similar functionality is achieved by appending to directives.
- Forces unconditional execution of the next CONFIG.SYS command.
ATemplate:NbndC
- Determines whether programs can be terminated upon encountering errors.
- Sets which drives record file access timestamps on FAT file systems.
- Enables conditional execution on AT-compatible hardware.
- Controls the boot manager functionality.
- Adjusts the verbosity level of error messages.
- Changes the default internal serial device driver assigned to the AUX: port.
- Prevents character devices from being accessible outside the virtual \DEV directory.
- Loads the fundamental device driver into system memory.
- Produces a brief beep even if sound notifications are disabled.
- Designates the next operating system to load during boot.
- Enables or disables extended Ctrl+C interrupt checking.
- Sets the quantity of disk buffers allocated by the system.
- Similar to BUFFERS but places buffers in HMA or UMB memory areas.
- Defines the highest number of cache blocks allocated from the system pool.
- Specifies maximum idle time before unused cache blocks return to the system pool.
- Determines maximum delay before dirty cache blocks are written back to disk.
- Loads and executes programs within CONFIG.SYS in the foreground, pausing further processing until completion.
- Configures Caps Lock key status on the keyboard.
- Specifies the driver name for CD-ROM hardware devices.
- Sets buffer count for CD-ROM data access operations.
- Continues processing of CONFIG.SYS directives from a new file or label.
- Defines the type of system clock used.
- Clears the screen display.
- Specifies OEM code page information for character encoding.
- Indicates CMOS RAM address location.
- Assigns color schemes for boot menu interfaces.
- , ;, ;, ;
- Set count, sequence, I/O addresses, and timeouts for corresponding COM ports (applicable from DR-DOS 7.02 onward).
- DMA buffer size configuration (specific to PTS-DOS).
- , ;, ;, ;
[Note: The list extends with further directive definitions related to device drivers, memory optimization, internationalization support, and conditional execution aimed at enhancing system efficiency.]
DTemplate:NbndF
- Manages relocation settings for drive descriptor tables.
- Specifies memory segment address used for multi-sector disk data deblocking processes.
- Activates support for an internal debugger tool.
- Controls boot manager operations.
- Loads device drivers into conventional memory space.
- Loads device drivers into upper memory blocks (consistent with DRDOS 5.0 behavior).
- Configures country-specific and codepage parameters for keyboard, screen, and printer devices.
- Adjusts sizes allocated to cache memory buffers.
- Sets compatibility mode parameters for floppy disk drives.
- Defines font settings for display output.
- Manages loading of DOS into high memory and utilization of upper memory areas.
- Loads DOS system tables (BUFFERS, FCBS, FILES, LASTDRIVE, STACKS) into upper memory regions.
- Specifies alternative directory paths for DOS system files.
- Defines search directories for data files required by DOS operations.
- Sets physical parameters for hard disk drives connected to the system.
- Specifies configuration parameters for unknown or unrecognized drives.
- Refer to .
- Enables error log creation and assigns drive location for PDUMP.nnn files.
- Displays a text message on screen output devices.
- Shows messages incorporating ANSI escape sequences for enhanced formatting.
- Adds extra validation checks when launching executable programs.
- Sets a predefined error or return code to be assumed thereafter by the system.
- Specifies A20 gate status upon program startup to control address line behavior.
- Terminates CONFIG.SYS processing prematurely except for SWITCHES and SHELL directives which continue execution.
- Defines size of hash tables used to accelerate file open operations (differs from MS-DOS FASTOPEN implementation).
- Configures number of cached File Control Blocks (FCBs) that can be open simultaneously (shares buffer with FILES in DR-DOS).
- Functions like FCBS but explicitly loads FCBs into upper memory areas for performance improvement.
- Boot manager control directive repetition for emphasis or additional options.
- Determines maximum number of simultaneously open files allowed by DOS.
- Similar to FILES but forces loading of file handles into upper memory explicitly for optimization purposes.
- Allows execution of selected CONFIG.SYS subsections as specified (see IGNORE directive).
GTemplate:NbndI
- Waits for a key press or timeout, setting the error level to the ASCII value of the key or 1024 if timed out.
- Resumes CONFIG.SYS processing at a designated label.
- Continues nested CONFIG.SYS processing at a specified label, then returns to the previous 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 after relocating the DOS data segment; compare with INSTCDEX.
- Refer to , , or for related commands.
- See also .
- Consult or for further guidance.
- Activates console and command line history buffer with advanced pattern search capabilities.
- Defines the address of the HMA segment.
- Configures energy-saving mode using the HLT instruction.
- Enables scanning of boot sector viruses.
- Loads installable file system drivers.
- Prevents execution of designated CONFIG.SYS subsections.
- Permits specific programs to execute at ring 2, allowing direct hardware I/O access.
- Incorporates directives from another menu block (emulated via GOSUB/RETURN in DR-DOS).
- Sets the status of keyboard Insert mode.
- Loads a TSR program into memory.
- Installs a TSR program into upper memory, equivalent to HIINSTALL in DR DOS 5.0.
- Loads a TSR program after relocating the DOS data segment, similar to INSTALL.
- Adjusts PIC interrupt priorities to prioritize a specified IRQ.
KTemplate:NbndM
- Defines keyboard layout configuration.
- Sets the address for the relocated keyboard buffer.
- Specifies the maximum number of accessible drives.
- Functions like LASTDRIVE but loads Current Directory Structure (CDS) into upper memory.
- Lists directories for DLL search paths.
- Manages compatibility with legacy applications.
- Determines the number of file locks allowed.
- Configures boot logo support and startup messaging using PTS-DOS boot manager.
- Defines count, order, I/O port address, and timeout settings for LPT1 device.
- Same as LPT1 configuration but applies to LPT2 device.
- Same as LPT1 configuration but applies to LPT3 device.
- Enables and configures LPT4 device with similar parameters.
- Sets delay before increasing process priority.
- Defines strategy for memory allocation management.
- Specifies default DOS memory allocation approach.
- Establishes menu option definitions.
- Sets colors used in menus (can be emulated via ECHO command in DR-DOS).
- Assigns default menu block (emulatable using TIMEOUT and SWITCH commands in DR-DOS).
- Defines multiple menu blocks (can be emulated through ECHO and SWITCH commands under DR-DOS).
- Enables multitrack disk operations support.
- Continues CONFIG.SYS processing in a separate file after loading a device driver and setting the %NEWFILE% environment variable.
NTemplate:NbndQ
- Defines default No () character response in Yes/No/Resume prompts.
- Sets keyboard [[Num Lock|Template:Keypress]] state on startup.
- Enables conditional execution based on the previous error code, such as .
- Displays text and waits for key input, similar to and commands in DR-DOS environments.
- Requires user confirmation upon errors during CONFIG.SYS processing.
- Configures buffer size allocated for LPT ports.
- Enables conditional execution on PC-compatible machines only.
- Adjusts scheduler priority settings.
- Sets priority levels for disk I/O related programs.
- Changes default printer device driver from LPT1 through LPT4 devices.
- Controls whether DOS-based programs are permitted to run.
- Loads user interface components during startup.
- Enables conditional execution on IBM PS/1-compatible systems only.
- Enables conditional execution on IBM PS/2-compatible systems only.
- Suppresses output sent to STDOUT.
RTemplate:NbndT
- Activates automatic system reboot upon encountering errors.
- Inserts annotations within CONFIG.SYS.
- Allocates a drive letter from local block device drivers.
- Sets the default Resume () character displayed in prompts.
- Returns control from nested CONFIG.SYS processing back to the previous GOSUB or SWITCH point, optionally with a return code.
- Defines the size of real mode memory available.
- Allows concurrent loading of programs in CONFIG.SYS, functioning similarly to INSTALL under DOS.
- Saves the initial character of deleted files in the FAT’s reserved area.
- Determines video mode (in FreeDOS) or screen access methods (in PTS-DOS).
- Controls the keyboard Scroll Lock state.
- Establishes environment variables.
- Loads the command interpreter shell.
- Functions like SHELL but permits pre-allocation of memory for COMMAND.COM within HMA or UMBs to optimize memory usage.
- Configures keyboard modifier keys such as Shift Lock, Num Lock, Scroll Lock, and Insert mode.
- Specifies whether files close when pressing Ctrl+Alt+Del.
- Bypasses POST during system reboot.
- , STACKSIZE, STACKSHIGH
- Set stack parameters across various DOS versions and embedded platforms, enhancing interrupt handling and memory allocation efficiency.
- , SYSBOOT, SYSGEN, SYSLOAD, SYSTOUMB
- PTS-DOS commands managing boot sequence, system memory layout, and loading procedures for streamlined startup and operation.
- , SWITCH, SWITCHES
- Commands enabling conditional processing and menu-driven configuration within CONFIG.SYS for adaptable system setup (not supported or emulated in certain DOS variants).
- , SWAPPATH
- OS/2 directives that regulate error logging locations and swap file paths to improve system reliability and management.
- , TIMEOUT, TIMESLICE
- Configure input parsing timeouts, prompt delays, and scheduler time slices to enhance user interaction and multitasking performance.
- , TRACE, TRACEBUF
- Manage temporary file extensions and enable detailed tracing or logging of CONFIG.SYS execution for diagnostic purposes (implementation varies by OS).
- , THREADS
- OS/2 commands that log error details and specify concurrent thread counts to optimize system performance and troubleshooting.
UTemplate:NbndZ
- Configures DOS to utilize a specified segment as Upper Memory Block (UMB) space.
- Sets which UMB server is employed.
- Defines address ranges designated as UMB RAM.
- Enables or disables verification of disk writes.
- Reports the DOS version presented to applications.
- Adjusts VGA display status settings.
- Specifies the current video mode in use.
- Determines whether virtual DMA is permitted.
- Enables or disables the processor’s Virtual Mode Extensions (VME).
- Configures Virtual Device Driver (VxD) settings for Windows.
- Sets system support parameters for Windows environments.
- Manages relocation of the Extended BIOS Data Area (XBDA).
- Executes conditionally on XT-compatible hardware platforms.
- Enables built-in Year 2000 compliance support.
- Defines the default affirmative character for Yes/No/Resume prompts.
- Controls tracking of deleted files.
Issues
Although the system can initiate booting without a valid CONFIG.SYS file or if it is corrupted, this file alongside AUTOEXEC.BAT remains critical for comprehensive operating system customization and meeting software prerequisites. Any damage to these files necessitates troubleshooting.
When CONFIG.SYS lacks a SHELL directive or if it is missing or corrupted, DOS attempts to locate COMMAND.COM in the root directory. Earlier versions prior to 6.0 will not proceed without it. MS-DOS 6.0, PC DOS 6.1, and Novell DOS 7 and later versions instead prompt users to specify a command processor path. This recovery prompt also appears if the main command interpreter fails or is intentionally exited, allowing limited shell substitution at runtime without requiring a reboot.
Due to incompatibility issues between MS-DOS 7.0+ COMMAND.COM and DR-DOS—especially since MS-DOS’s version often resides in C:\ within dual-boot configurations—DR-DOS version 7.02 and newer restrict bypassing SHELL directives during skip/trace/step modes to prevent conflicts. Some later revisions introduced shortcuts enabling recovery from invalid SHELL parameters by reactivating skip behavior and prompting for a valid shell filename before loading COMMAND.COM.
Limits on CONFIG.SYS file sizes differ: MS-DOS/PC DOS restricts files to several kilobytes (up to approximately 64 KB in recent releases), whereas DR-DOS imposes no practical size restriction because it interprets lines sequentially rather than tokenizing them. This approach grants DR-DOS users comprehensive control over driver and TSR loading order via DEVICE and INSTALL commands, facilitating resolution of loading conflicts or conditional integration of temporary software into the boot sequence based on factors such as processor type, key presses, errors, or return codes.
In MS-DOS/PC DOS versions from 2.0 through 4.01, the SHELL directive was limited to a maximum length of 31 characters. Later editions increased this limit up to 128 characters, while DR-DOS accepts up to 255 characters. Note 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, the original CONFIG.SYS and AUTOEXEC.BAT files are renamed to CONFIG.DOS and AUTOEXEC.DOS to enable dual-boot functionality. During a DOS boot, these renamed files are temporarily switched back to their standard filenames. Additionally, backup copies of Windows 95's versions are saved as CONFIG.W40 and AUTOEXEC.W40.
In cases where Caldera DR-DOS 7.02 or 7.03 is set up alongside Windows 95, the Windows CONFIG.SYS and AUTOEXEC.BAT files remain untouched. Instead, DR-DOS relies on DCONFIG.SYS and AUTODOS7.BAT as its startup configuration files.
OS/2 / Windows NT
OS/2 makes extensive use of CONFIG.SYS to load drivers and configure the environment prior to launching its graphical user interface.
Within the OS/2 subsystem of Windows NT, CONFIG.SYS is represented as a configuration stored in the registry, accessible to OS/2 applications.
There are numerous undocumented CONFIG.SYS commands specific to OS/2.
CONFIG.SYS continues to play a crucial role in OS/2-based operating 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 directive descriptions
- User Manual for PTS-DOS 2000 Pro including CONFIG.SYS directives (partial)
- German-language unofficial PTS-DOS FAQ (2004) with additional CONFIG.SYS directives
- ↑ Cite error: Invalid
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