Category Archives: x87

Learn Something Old Every Day, Part VIII: RTFM

Posted on August 22, 2023 by Michal Necasek

In my quest to understand the intricacies of x87 behavior and especially floating-point exceptions, I pulled out my trusty old Alaris Cougar board. The system board had a 100 MHz Intel OverDrive 486 DX4 plugged in and worked quite well. … Continue reading →

Posted in 486, Documentation, Intel, PC hardware, x87 | 9 Comments

This Code Smells of Desperation

Posted on August 5, 2023 by Michal Necasek

A few weeks ago I had the questionable pleasure of diving into the math exception handler of WIN87EM.DLL, the Windows 3.1 math emulator and FPU support library. Actually WIN87EM.DLL appears to have been first shipped with Windows 3.0, and the … Continue reading →

Posted in Bugs, Microsoft, PC architecture, x87 | 19 Comments

Failing to Fail

Posted on June 16, 2023 by Michal Necasek

The other day I was going over various versions of the venerable DOS/16M DOS extender from Rational Systems (later Tenberry Software). The DOS/16M development kit comes with a utility called PMINFO.EXE which is meant to give the user some idea … Continue reading →

Posted in Bugs, Intel, PC architecture, x87 | 11 Comments

Learn Something Old Every Day, Part VII: 8087 Intricacies

Posted on January 23, 2023 by Michal Necasek

The other day I investigated a report that a C runtime library modification causes programs to hang on a classic IBM 5150 PC with no math coprocessor. The runtime originally contained two separate routines, one to detect the presence of … Continue reading →

Posted in 8086/8088, Development, IBM, Intel, PC history, x87 | 10 Comments