Instruction decoding in the 8087 has many more complications: hardcoded instructions handled by the "Bus Interface Unit", instructions that load a constant from the constant ROM, and handling the instruction queue. For more details, see my latest blog post:
https://www.righto.com/2026/02/8087-instruction-decoding.html
Ken Shirriff
@kenshirriff@oldbytes.space
Computer history. Reverse-engineering old chips. Restored Apollo Guidance Computer, Xerox Alto. Ex-Google, Sun, Msft. So-called boffin.
oldbytes.space
Ken Shirriff
@kenshirriff@oldbytes.space
Computer history. Reverse-engineering old chips. Restored Apollo Guidance Computer, Xerox Alto. Ex-Google, Sun, Msft. So-called boffin.
oldbytes.space
@kenshirriff@oldbytes.space
·
Feb 14, 2026
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