Math Coprocessor Detection Hangs System in QBasic (72412)

The information in this article applies to:
    Microsoft MS-DOS operating system 5.0
    Microsoft MS-DOS operating system 5.0a
    Microsoft MS-DOS operating system 6.0
    Microsoft MS-DOS operating system 6.2
    Microsoft MS-DOS operating system 6.21
    Microsoft MS-DOS operating system 6.22

This article was previously published under Q72412


When starting MS-DOS QBasic (included with MS-DOS versionS 5.x and 6.x) your system may stop responding (hang).


This problem occurs because of the way the QBasic environment checks for the presence of a math coprocessor chip in your computer.


Microsoft has confirmed this to be a problem with MS-DOS versions 5.0, 5.00a, 6.0, 6.2, 6.21, and 6.22. We are researching this problem and will post new information in the Microsoft Knowledge Base as it becomes available.


If this problem occurs, reboot your machine and add the following line to your AUTOEXEC.BAT file:


After you add this line to the AUTOEXEC.BAT file, reboot your machine so that this switch can take effect. You should now be able to enter the QBasic interpreter with no difficulty.

NOTE: Setting NO87 does not affect other applications' use of a math coprocessor (with the exception of MS-DOS 6.00 DoubleSpace) because the application has to look for this environment variable.

The environment variable NO87 is a switch to tell the QBasic interpreter that there is no 80x87 chip in your machine. You can set this variable to any value to make NO87 true. Setting NO87 to null (SET NO87=<Enter>) makes NO87 false, which is the default state.

Although the QBasic interpreter checks for a coprocessor, it doesn't actually use the coprocessor even if it successfully detects one. You do not lose any functionality or speed by setting the NO87 variable to true, even if you have a math coprocessor chip.

The same problem occurs in QuickBasic version 4.5, but the QuickBasic environment can use the coprocessor if it is successfully detected.

Modification Type: Major Last Reviewed: 5/10/2003
Keywords: KB72412