The Story Behind x86's UD2 Undefined Instruction Name Explained

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A technical blog post on Microsoft's Old New Thing explores the naming of the x86 undefined instruction known as UD2. The article investigates why the instruction carries the number 2 in its name, suggesting a predecessor or versioning history behind the designation. The post was shared on Hacker News, attracting early reader interest and discussion. It dives into low-level CPU architecture history, shedding light on how Intel formally defined an instruction guaranteed to trigger an invalid opcode exception.

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