A closer look at AMD EPYC 9704 Bergamo CPUs

AMD launched its 4th gen EPYC 9004-series CPUs last November to critical acclaim, with hugely improved performance over their 3rd gen 7003-series predecessors. Later on, AMD expanded the range with special X models with massively expanded Level 3 cache of over a gigabyte for scientific computing workloads.

A large part of the attraction of EPYC 9004, both the original standard models and later X models, was the maximum core count of 96, way beyond anything Intel could offer with its Xeon CPUs. AMD’s latest EPYC 9704 CPUs, codename Bergamo, extend AMD’s lead even further, with an incredible 128 cores on offer.

This leap forward in core density is made possible by adjusting the Zen 4 architecture in 96-core EPYCs into a new variant called Zen 4c. The benefit of this approach is that Zen 4 and Zen 4c EPYCs all use the same SP5 socket and so work in the same servers, helping to keep costs down.

The biggest difference between Zen 4 and Zen 4c, no pun intended, is that the latter has less Level 3 cache – 2MB per core rather than the usual 4MB. The resulting Zen 4c die is a considerably more compact and has shorter trace lengths than Zen 4.

In addition, Zen 4c cores are arranged in multiples of 16, as opposed to multiples of eight Zen 4 cores, as AMD uses a flexible chiplet design for all its EPYC CPUs. To the outside world, Zen 4c and Zen 4 are identical, both having 128 PCIe 5.0 lanes and 12-channel DDR5 memory.

At launch there are three EPYC 9704 CPUs based on the Zen 4c architecture in production, the flagship 128-core / 256-thread 9754, the mid-spec 128-core / 256-thread 9754S and the entry-level 112-core / 224-thread 9734, although it feels odd to describe a CPU like this as entry-level.

These three EPYC 9704 Zen 4c processors aren’t meant to be the kings of the EPYC 9004-series stack. Yes, they have the highest number of cores, but that isn’t everything when it comes to server performance. Where Zen 4c CPUs will excel is cloud native applications as you’ll be able to run considerably more VMs on a server than one with standard Zen 4 CPUs, let alone Intel Xeon processors with their even lower core density.

There is also a trade-off in terms of clock frequency compared to Zen 4 CPUs, but given the target market for Zen 4c CPUs this shouldn’t really be a problem and is precisely why AMD now has an extensive product stack of three different EPYC 9004-series CPUs, each optimised for different workloads.

Continue reading about all the different types of AMD EPYC 9004 CPU and how as an AMD EPYC Elite Partner Scan 3XS Systems can design and build you custom servers.