Pentium FDIV bug – 25 years ago; Ken Shirriff reverse engineerded the cause under a microsope
Posted by jpluimers on 2024/12/31
A small introduction is the Pentium FDIV bug – Wikipedia article which already has some of the highlights..
Ken Shirriff however went all the way in, and used a microscope to focus in on to the actual cause.
He wrote two Mastodon threads on it watching (most recent first, with a link to his blog post) making a good year’s end read:
- [Wayback/Archive] Ken Shirriff: “In 1994, a math professor disc…” – OldBytes Space – Mastodon
In 1994, a math professor discovered that Intel’s Pentium chip sometimes gave the wrong answer when dividing. Fixing this “FDIV” bug cost Intel $475 million. I analyzed the Pentium chip and found the bug. 1/N
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[Wayback/Archive] Intel’s $475 million error: the silicon behind the Pentium division bug
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- [Wayback/Archive] Ken Shirriff: “Intel launched the Pentium pro…” – OldBytes Space – Mastodon (9 posts)
In 1994, a math professor discovered that Intel’s Pentium chip sometimes gave the wrong answer when dividing. Fixing this “FDIV” bug cost Intel $475 million. I analyzed the Pentium chip and found the bug. 1/N
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And there is of course this, that predated his microscope work [Wayback/Archive] Ken Shirriff: “I recently saw an amazing Navajo rug…” – OldBytes Space – Mastodon
I recently saw an amazing Navajo rug at the National Gallery of Art. It looks abstract at first, but it is a detailed representation of the Intel Pentium processor. Called “Replica of a Chip”, it was created in 1994 by Marilou Schultz, a Navajo/Diné weaver and math teacher. Intel commissioned the weaving as a gift to the American Indian Science & Engineering Society.
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The weaving of a Pentium is so accurate that I could label the functional blocks of the processor. Amusingly, the gallery hung the weaving backward. The wrong side is facing outward, so the chip is mirrored. I had to flip the image to make this diagram.
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--jeroen
The Wiert Corner - irregular stream of stuff 
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