Processor: Early Intel Pentium

Year: 1993-1994

Continuing their massively successful x86 processor product line, in 1993 Intel launched the significantly advanced Pentium procesor.  A marked techonological step from its predecessors, this chip included many new features, such as a superscalar architecture (parallel execution units for simultaneous dispatch of two independent instructions) and vast improvements to floating-point processing capability.  But buried within the latter was a bug in the chip hardware, which derailed the fanfare of this new design and cost Intel clout -- as well as $475 million in replacements.

The problem stemmed from a new algorithm used internally to do the floating-point division operation.  Instead of the slower traditional method of processing the number one bit at a time, the new algorithm consumed data in larger chunks.  These chunks were then used to index results within a look-up table -- similar to the "times tables" in reverse.  The mistake, however, was reportedly missing entries in this table.  For this reason, certain processing steps would default to a zero entry, causing inaccuracies in the calculations involving these entries.  Although the effected operations were relatively rare in occurrence, these fault cases cluster around certain values, and critics (like Intel's competition) claimed these numbers were more common in day-to-day calculations.

This exhibit showcases one of these faulty Pentium processors, a P5-90.  We wrote software that can perform floating-point operations on-demand or scan for calculation errors at random.

To this end, though, the Pentium recovered from its fractious beginnings to continue Intel’s dominance supplying PC processors.  In fact, enhancements to floating-point performance of the Pentium ultimately proved a decisive blow to competitors like Cyrix, whose chips’ less-advanced approach could not keep up with the newest generation of demanding video games, like id Software’s Quake.

Q: How many Pentium designers does it take to screw in a light bulb?

A: 1.99904274017, but that's close enough for non-technical people.