The original Pentium was power-hungry, so Intel soon released an updated version that could turn off the clock to parts that weren't being used, saving power. The original (P5 architecture, part number 80501) on the left has a noticeably larger die and package than the update (P54C, 80502). The original was built with Intel'ss 800 nm BiCMOS process, while the update was 600 nm.
Here's a closeup of the die showing the Pentium Processor name and the Intel copyright. The M-in-a-circle is a Mask Work symbol, like a copyright but for IC masks. I convinced the Unicode Consortium to add the symbol to Unicode, but I don't think any fonts support it yet: 🆭
Edit: seems like the symbol works for lots of people.
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