AMD’s 3rd Gen Ryzen 3 CPU, the 3100 and the 3300X are both quad-core chips with SMT and 18MB of total cache memory. On the outside, the only difference between the two is with respect to the clock speeds, but it turns out that the CCX configuration of the two processors is also quite different.
Both the CPUs use one CCD, but within it, there are two CCXs. The Ryzen 3 3100 uses two cores from one CCD (out of four) and two from the other. The L3 cache is also distributed similarly. Half of the cache is from one CCX while the other half is from the second one.
The 3300X, on the other hand, just leverages one of the CCXs while the other is disabled. All four cores and the entire 16MB of L3 cache is from the same CCX. This means that the 3300X will have lower core-to-core latencies, resulting in better performance in latency-sensitive applications such as gaming.
What this basically means is that AMD is utilizing the absolute last bits of the Zen 2 silicon to fabricate the Ryzen 3 chips. As such, you can expect that the amount of silicon wasted in fabbing these processors is very less.