OS/2 FAQ List: User's Edition (4 Apr 94)

(5.9) Specific DOS Sessions

How do I boot a real version of DOS from within OS/2 2.1?

Booting a real version of DOS under OS/2 provides certain features that 
the OS/2 emulated DOS sessions cannot.  For example, a specific DOS 
session can provide access to devices (like CD-ROM drives) and networks 
for which there are only DOS device drivers.  A specific DOS session can 
also help get DOS applications which generate spurious "divide by zero" 
errors running again.

You will be able to run one such session per hardware device.  So, for 
example, if you have your DOS networking software loaded in one specific 
DOS session, you may not start another, similar session.

Specific DOS sessions are discussed in the online Command Reference (under 
VMDISK), the Master Help Index, and the printed Installation Guide 
(Appendix E).  You should consult those resources first.  However, if you 
are still unsure how to configure your system to run specific DOS 
sessions, follow these steps:

  1. Create a bootable DOS diskette.  Insert your DOS system diskette into 
     Drive A and reboot.  When you arrive at the "A>" prompt, type 
     FORMAT A: /S and press ENTER.  (Note that you may wish to format the 
     diskette for the smallest capacity possible, to save hard disk space 
     later on.  For example, a 5.25 inch double density -- not high 
     density -- diskette may be formatted to just 160K by adding the 
     /1 /N:8 parameters to the FORMAT command.)  When prompted, insert a 
     blank diskette into Drive A and press ENTER.  When the FORMAT 
     operation is complete, remove the diskette and restart OS/2.

  2. Copy FSFILTER.SYS to the diskette.  Double click on OS/2 System -> 
     Command Prompts -> OS/2 Window.  Insert the diskette you just 
     formatted into Drive A.  Copy the following file to your startable 
     diskette: \OS2\MDOS\FSFILTER.SYS.

  3. Set up CONFIG.SYS.  Using a text editor (like the OS/2 System Editor) 
     create the file A:\CONFIG.SYS with the following lines at the top:

     DEVICE=FSFILTER.SYS
     DEVICE=C:\OS2\MDOS\HIMEM.SYS
     DEVICE=C:\OS2\MDOS\EMM386.SYS
     DEVICE=C:\OS2\MDOS\ANSI.SYS

     Change the "C:" drive letter if OS/2 is installed on another drive. 
      Add any other lines as required for your application (like CD-ROM or 
     networking), but do not include any XMS, EMS, mouse, or memory 
     management device drivers.  Make sure that everything is referenced 
     with a drive letter and path, as above.

  4. Set up AUTOEXEC.BAT.  Likewise, create a file named A:\AUTOEXEC.BAT 
     and make sure that the first line reads:

     C:\OS2\MDOS\MOUSE

     changing "C:" if necessary.  Add any additional lines (like PATH, 
     SET PROMPT, and so on) as required by your application.  Make sure 
     that \OS2\MDOS is referenced in the PATH.

  5. Test your DOS diskette.  Once you have configured the CONFIG.SYS and 
     AUTOEXEC.BAT files as you wish, double click on OS/2 System -> 
     Command Prompts -> DOS from Drive A:.  A DOS session should start. 
      Test for the functionality you need (like access to your CD-ROM 
     reader or network).  If the session is not working properly, press 
     CTRL-ESC and shut down the session, edit CONFIG.SYS and/or 
     AUTOEXEC.BAT as required, and repeat the test.

  6. Create the diskette image.  When you are satisfied that your specific 
     DOS session diskette functions properly, go back to the OS/2 Window 
     and type VMDISK A: C:\DOS.IMG to create a diskette image file.  (If 
     you want the file to be located on another drive or in another 
     directory, change "C:\" accordingly.)

  7. Create a program object for your specific DOS session.  Drag a 
     program object from your Templates folder to any target folder.  When 
     the notebook opens, enter a single asterisk (*) in the Program Name 
     field, then click on the right arrow in the lower right.  Select 
     either DOS Window or DOS Full Screen for the session type, as 
     desired.  Click on the DOS Settings button, and scroll down until you 
     find the DOS_STARTUP_DRIVE property.  Enter C:\DOS.IMG in the field 
     at the upper right.  (If your image file is not located on Drive C in 
     the root directory, make the necessary changes.)  Change any other 
     DOS Settings if necessary.  Click on the Save button, then click on 
     the General tab.  Give your program object a name.  Then close up the 
     notebook.

 You should now be able to double click on your new program object to 
 start your specific DOS session.  If you require access to your diskette 
 drive (Drive A), use the FSACCESS command.  See the online Command 
 Reference for details.

 When formatting your bootable DOS diskette, you may wish to use 
 additional command line parameters to create a diskette with a reduced 
 capacity.  The "smaller" the diskette, the less room the diskette image 
 file created by VMDISK will take on your hard disk.  See your DOS manual 
 for details, or use the example given above.

 Related information:

 (1.3) DOS and Windows Compatibility

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