Learn Something Old Every Day, Part XVIII: How Does FPU Detection Work? (os2museum.com)

The OS/2 Museum article explains how x86 CPUs detect whether an x87 FPU is present, tracing the evolution from the 8086/8087’s ESC/WAIT behavior to the 286/287 and beyond. It notes that early BIOS “FPU present” bits could be unreliable due to incorrect user switch guidance, and that later detection largely requires software to infer FPU availability rather than relying on hardware signals. The post also describes how the CPU and FPU exchange work via ESC opcodes and busy-line/implicit synchronization rules, highlighting why naive detection can hang on older systems.