AMD Zen 4c Not an E-core, 35% Smaller than Zen 4, but with Identical IPC
AMD on Tuesday (June 13) launched the EPYC 9004 "Bergamo" 128-core/256-thread high density compute server processor, and with it, debuted the new "Zen 4c" CPU microarchitecture. A lot had been made out about Zen 4c in the run up to yesterday's launch, such as rumors that it is a Zen 4 "lite" core that has lesser number-crunching muscle, and hence lower IPC, and that Zen 4c is AMD's answer to Intel's E-core architectures, such as "Gracemont" and "Crestmont." It turns out that it's neither a lite version of Zen 4, nor is it an E-core, but a physically compacted version of the Zen 4 core, with identical number crunching machinery.
First things first—Zen 4c has the same exact IPC as Zen 4 (that's performance at a given clock-speed). This is because its front-end, execution stage, load/store component, and internal cache hierarchy is exactly the same. It has the same 88-deep load queue, 64-deep store queue, the same 675,000 µop cache, the exact same INT+FP issue width of 10+6, the same exact INT register file, the same scheduler, and cache latencies. The L1I and L1D caches are the same 32 KB in size as "Zen 4," and so is the dedicated L2 cache, at 1 MB.
First things first—Zen 4c has the same exact IPC as Zen 4 (that's performance at a given clock-speed). This is because its front-end, execution stage, load/store component, and internal cache hierarchy is exactly the same. It has the same 88-deep load queue, 64-deep store queue, the same 675,000 µop cache, the exact same INT+FP issue width of 10+6, the same exact INT register file, the same scheduler, and cache latencies. The L1I and L1D caches are the same 32 KB in size as "Zen 4," and so is the dedicated L2 cache, at 1 MB.