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Category Archives: x87
Minor 387 Documentation Mystery
So here I am, writing a bit of test code to figure out the behavior of x87 FPUs with regard to saving and loading the FPU state (FSTENV/FLDENV and FSAVE/FRSTOR instructions in different modes and formats). The original real-mode only … Continue reading
Posted in Documentation, Intel, x87
9 Comments
Learn Something Old Every Day, Part VIII: RTFM
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
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
22 Comments
Failing to Fail
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
13 Comments
Learn Something Old Every Day, Part VII: 8087 Intricacies
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