Microcode inside the Intel 8087 floating-point chip: register exchange

Intel's 1980 8087 floating-point co-processor accelerated floating-point calculations up to 100 times faster and established a standard still used today, with its functionality controlled by microcode stored in a ROM. Researchers from the Opcode Collective are reverse-engineering the 8087's microcode to understand how it implements complex algorithms; their analysis reveals that even simple operations like the FXCH (register exchange) instruction require 14 micro-instructions to execute. The chip's 1,648 microcode instructions manage calculations across temporary and stack registers using a 16-bit instruction format that specifies operations such as data transfers, shifts, and arithmetic functions.