CCX is a term used in AMD CPUs and stands for CPU complex or core complex. It refers to a group of four CPU cores and their CPU caches (L1, L2, L3). AMD’s Infinity Fabric connects multiple CCXes together to create Ryzen processors. You’ll find this term used in reference to CPUs running on AMD’s Zen and Zen+ microarchitectures, aka Ryzen-series CPUs.
Each CPU built on one of these architectures uses CCX clusters. For the Ryzen 3000-series processors, CCX refers to a four-core grouping inside of each core chiplet die (CCD). For example, an AMD CPU with 8 cores will have a CCD with two 4-core CCXs.
Below is a Ryzen Threadripper CPU with 2 die. You can see each die has 2 CCXs, for a total of 16 cores.
For another example, let’s turn to a less core-heavy CPU, the AMD Ryzen 9 3900X. A simple spec sheet will tell you the CPU has 12 cores in total. But with our knowledge that this CPU is based on the Zen 2 microarchitecture, we know that those 12 cores live in 2 CCXes within each of the CPU’s CCD. Had enough acronyms yet?
The 3900X is also specced to have 64MB total of L3 cache. Ryzen 3000-series CPUs with more than 8 cores have 2 CCDs (instead of 1). And, as mentioned, CCXs share Level 3 cache. Therefore, each CCX in the 3900X has 16MB of shared cache. That equates to 32MB of L3 cache per CCD (16MB x 2 CCXs) or 64MB for the whole CPU (32MB x 2, since there are 2 CCDs in the processor).
What if the total number of cores in the CPU isn’t divisible by 4? For instance, the AMD Ryzen 5 3600 has 6 cores. Well, this CPU still has 2 CCXes; however one core in each CCX is disabled. This is a common practice in CPU binning.
This article is part of the Tom's Hardware Glossary
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