The first Pentium!

This distinctive specimen is a gold topped Pentium running at a blistering 60MHz, which made the headlines soon after release due to the now infamous FDIV-bug.

In late summer of 1994 a mathematician from USA detected that the FPU of the Pentium core in some cases didn't divide as accurately as it should. Not only the P-66, but the P-75, P-90 and P-100 all had the same flaw. Unfortunately, Intel made some bad decisions at this point which severely harmed their reputation. After a phase of denial, Intel offered a replacement chip to any customer who could prove that they did scientific computing with the Pentium.

You could easily see if your Pentium was flawed by a simple division using the ordinary calculator program that came with Windows. Intel's reputation was at stake - you simply couldn't rely on a Pentium based computer producing the right results anymore.

Towards the end of 1994 they offered replacement chips for any flawed Pentium. Even today you can still get a replacement chip for your old Pentium (like this one).

Unfortunately, too many people returned their flawed CPUs which is very sad from a collector's perspective.
An interesting note is that Intel had already discovered this flaw before the matter became public while they were working on a FPU for the Pentium-Pro.