CCX or core complex is a lower level grouping of cores. On Zen 2/3 the CCX would have 4 cores on a little ring bus. A full 8-core CCD would then have two of tho

CCX or core complex is a lower level grouping of cores. On Zen 2/3 the CCX would have 4 cores on a little ring bus. A full 8-core CCD would then have two of those 4-core CCXs connected via infinity fabric. The inter-CCD connections were also made with infinity fabric between the CCXs. Zen 4 increases the CCX size to 8, so each CCD only has one. I can't remember exactly how Zen 1 worked but I think it was different.