https://www.mail-archive.com/search?l=cctalk@classiccmp.org&q=subject:%22%5C%5Bcctalk%5C%5D+Re%5C%3A+undocumented+instructions+including+HCF+%5C%5Bwas%5C%3A+System+360+question%5C%5D%22&o=newest&f=1
subject:"\[cctalk\] Re\: undocumented instructions including HCF \[was\: System 360 question\]"
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https://hackaday.com/2023/07/17/finding-undocumented-8086-instructions-via-microcode/
Finding Undocumented 8086 Instructions Via Microcode | Hackaday
Jul 17, 2023 - Video gamers know about cheat codes, but assembly language programmers are often in search of undocumented instructions. One way to find them is to map out all...
findingundocumented8086instructionsvia