Yes, that may actually look more like a game cartridge circa 1985, but it's actually a Slot 2 Pentium II Xeon CPU. Why such a gigantic cartridge? A product of 1998, it was built on a 0.25-micron process. In today's terms, that's a 250-nanometer process—for comparison, a modern Skylake CPU is built on a 14-nanometer process.
Back then it wasn't possible to integrate much cache into chip, so Intel put the L2 cache (up to 2MB) on chips placed next to the CPU and connected it via a secondary "back side bus." Before the use of a cartridge design, external cache was placed on the motherboard, which greatly reduced overall speed because it was farther away and could induce quality control issues. One other interesting fact: A Pentium II Xeon at 400MHz sipped just 18.6 watts, which would make it a mobile CPU today.