Intel's Pentium FDIV Bug: A $475 Million Mistake

In 1993, Intel launched the high-performance Pentium processor. A year later, a flaw in its floating-point division algorithm was discovered, causing incorrect results in rare cases. Initially dismissed by Intel, the bug—dubbed the FDIV bug—quickly gained media attention. The error stemmed from 16 missing entries in the processor's lookup table, with 5 entries directly causing incorrect calculations. Intel ultimately recalled and replaced all affected chips at a cost of $475 million. This article delves into the Pentium's division algorithm, pinpoints the bug's location on the chip, and explains the underlying mathematical error that led to this costly mistake.