KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q32098: QB Program Can Hang If Coprocessor Switch Is Set Incorrectly

Article: Q32098
Product(s): See article
Version(s): 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 1-SEP-1989

QuickBASIC Versions 4.00b and 4.50, and programs compiled with
Microsoft BASIC Compiler Versions 6.00 and 6.00b for MS OS/2 and
MS-DOS or its copy of QuickBASIC, detect the presence or absence of a
math coprocessor differently than QuickBASIC Version 4.00 does.

QuickBASIC Version 4.00 loads and runs on a standard IBM PC even when
the coprocessor switch on the PC motherboard is incorrectly set to
indicate the presence of a math coprocessor when one is not actually
present. Programs run in QuickBASIC versions later than 4.00 (in the
QB.EXE editor or from an executable .EXE program) will hang under
these same conditions.

If you suspect that the hardware switch for the coprocessor is set
incorrectly, type the following DOS command to turn off coprocessor
checking and try the program again:

   SET NO87="Coprocessor has now been disabled."

If the program now runs without hanging, then the hardware switch for
the coprocessor is probably incorrectly set to indicate that a
coprocessor is installed when one is not actually present. Another
possibility is that the installed coprocessor wrongly has a speed
(Megahertz) rating faster than the CPU (central processing unit) --
the coprocessor's speed must be equal to or less than the speed of
the CPU.

Some customers have reportedly run QuickBASIC Version 4.00 without
problems on older PCs and did not realize that the hardware switches
were set incorrectly until they tried the QuickBASIC Version 4.00b
upgrade and their machines hung.

According to one customer, his original IBM documentation listed the
coprocessor switch as unused, and two of his machines came from IBM
with the switches set in what is now considered the incorrect
position.

One customer with an "original" PC 1 from IBM (with a BIOS dated
10-27-1982, and 16/64K stamped on the motherboard) found that the IBM
PC documentation was wrong for Switch Block One on the PC System
Board. Switch number 2 must be ON in Switch Block One for a computer
that has no coprocessor.

Please refer to Page 457 of the following book for a correct list of
all switch settings for the IBM PC:

   "The Programmer's PC Sourcebook" by Thom Hogan (published by
   Microsoft Press, 1988)

This book contains reference tables for IBM PCs and compatibles, PS/2
machines, and MS-DOS.

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.