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The Config.sys Documentation Project
  1. BASEDEV Statements
  2. CALL Statements
  3. DEVICE Statements
  4. IFS Statements
  5. OS/2 Commands
  6. DOS Commands
  7. RUN Statements
  8. SET Statements
  9. PSD Statements
  10. Other Information
  1. Programs
  2. Hardware
  3. List of Statements


With this entry you can stop DOS applications by pressing CTRL + BREAK. This slows the application down a bit, but you can immediately stop an application without waiting for the process to end.

Note: For DOS programs only!


Parameters: Value can be ON or OFF.

  • BREAK=ON - After pressing CTRL + BREAK the process stops immediately.
  • BREAK=OFF - After pressing CTRL + BREAK the process runs until it reads from the prompt.

There is no default value.


This statements sets the number of file buffers for the FAT file system. Each buffer uses 512 bytes of RAM.


Default settings:



  • BUFFERS=X - (from 3 -100) Value can be in the range from 1 to 100.

If this statement is not set it defaults to 5

TIP: Disk buffers are blocks of memory set aside by OS/2 for use in reading and writing blocks of data. For example, if a program wants to change 80 bytes of a file, it needs to read the 512 byte sector that contains the original data, change the information and then write the corrected 512 byte sector back out. A "buffer" is the 512 byte temporary staging area for this partial sector operation. According to a source at IBM, "OS/2 allows multiple simultaneous I/O operations to be queued up for both diskette and hard disk. Each 'concurrent' operation may need a buffer. If there are not enough buffers, overlap can be inhibited. Because OS/2 has more 'simultaneous' queued I/O than DOS, it needs more buffers."

TIP: Generally, if you are running FAT on one or more of your hard drives, you can speed up your system by increasing the number of BUFFERS. But, keep in mind that as you increase the number, you reduce available memory. Be careful about using a lower number unless you only have 4MB of RAM. With 4MB of RAM you may wish to set BUFFERS to 20.

TIP: If you are using only HPFS (i.e., no FAT partitions), try setting BUFFERS to 3. With HPFS you generally don't need BUFFERS. Remember that 3 is the minimum parameter. If you set BUFFERS to 1 or 2, OS/2 will default to 30 since 1 and 2 are out of range. There is one exception to this tip. If you access your floppy disks or FAT formatted removable disks a lot, then a reduced BUFFERS setting could impact the performance of these drives. (Thanks to Andrew Stephenson for reminding me to integrate removable drives also).


Loads DOS device driver to upper memory


This entry is used to select whether the DOS kernel should be loaded into the high memory area and whether DOS should use the upper memory blocks.

Note: The DOS entry is also available from the settings notebook of any DOS or Windows application.


Default settings:



  • HMA can be LOW or HIGH.

This parameter is for the kernel load area.

  • UMB can be UMB or NOUMB.

This parameter is for the upper memory blocks.


This command is only used by old DOS applications. They need the command to store data about open files. Newer DOS programs work with the files command. You can set the command to FCBS=4,2 to save some RAM.

Note: The FCBS command is also available in the settings notebook for every DOS program.

FCBS=<max>,<don't close>
Ex: FCBS=16,8


  • <max>

Max can be in the range from 1 to 255.

  • <don't close>

Don't close is an optional parameter and defines the number of files which can't be closed. They can be in the range from 0 to 254 but they must be smaller than the <max> parameter.


Defines the maximum concurrently open files in a DOS session.


Default settings:

  • FILES=20


Value can be in the range from 20 to 255.


This command defines the command line for the DOS shell.

SHELL=Shell [shell parameters]

Default settings:


Parameters: Shell can be any valid DOS shell.


Shell parameters can be any parameters and commands you can pass to the shell See the documentation for the shell you use for more information.