Zen 2 is the codename for a computer processormicroarchitecture by AMD. It is the successor of AMD's Zen and Zen+ microarchitectures, fabricated on the 7 nanometerMOSFET node from TSMC and powering the third generation of Ryzen processors, known as Ryzen 3000 for the mainstream desktop chips and Threadripper 3000 for high-end desktop systems. The Ryzen 3000 series CPUs were released on July 7, 2019, while the Zen 2-based Epyc server CPUs were released on August 7, 2019. An additional Ryzen 9 3950X was released in November 2019. At CES 2019, AMD showed a Ryzen third-generation engineering sample that contained one chiplet with eight cores and 16 threads. AMD CEO Lisa Su also said to expect more than eight cores in the final lineup. At Computex 2019, AMD revealed that the Zen 2 "Matisse" processors would feature up to 12 cores, and a few weeks later a 16 core processor was also revealed at E3 2019, being the aforementioned Ryzen 9 3950X. Zen 2 includes hardware mitigations to the Spectre security vulnerability. Zen 2-based EPYC server CPUs use a design in which multiple CPU dies manufactured on a 7 nm process are combined with a 14 nm I/Odie on each multi-chip module package. Using this, up to 64 physical cores and 128 total compute threads are supported per socket. This architecture is nearly identical to the layout of the "pro-consumer" flagship processor Threadripper 3990X. Zen 2 delivers about 15% more instructions per clock than Zen and Zen+, the 14 and 12nm microarchitectures utilized on 1st and 2nd generation Ryzen respectively.
Design
Zen 2 is a significant departure from the physical design paradigm of AMD's previous Zen architectures, Zen and Zen+. Zen 2 moves to a multi-chip module design where the I/O components of the CPU are laid out on its own, separate die, which is also called a chiplet in this context. This separation has benefits in scalability and manufacturability. As physical interfaces don't scale very well with shrinks in process technology, their separation into a different die allows these components to be manufactured using a larger, more mature process node than the CPU dies. The CPU dies, now more compact due to the move of I/O components onto another die, can be manufactured using a smaller process with fewer manufacturing defects than a larger die would exhibit while also allowing for more dies per wafer. In addition, the central I/O die can service multiple chiplets, making it easier to construct processors with a large number of cores. With Zen 2, each CPU chiplet houses 8 cores, arranged in two of 4 cores each. These chiplets are manufactured using TSMC's 7 nanometer MOSFET node and are about 74 to 80 mm2 in size. The chiplet has about 3.9 billion transistors, while the 12 nm IOD is ~125 mm2 and has 2.09 billion transistors The amount of L3 cache has been doubled to 32 MiB, with each core on an 8-core chiplet now having access to 4 MiB of L3 compared to the 2 MiB of Zen and Zen+. AVX2 performance is greatly improved by an increase in execution unit width from 128-bit to 256-bit. There are multiple variants of the I/O die: one manufactured on GlobalFoundries14 nanometer process, and another manufactured using the same company's 12 nanometer process. The 14 nanometer dies have more features and are used for the EPYC Rome processors, whereas the 12 nm versions are used for consumer processors. AMD's Zen 2 architecture can deliver higher performance at a lower power consumption than Intel's Cascade Lake architecture, with an example being the AMD Ryzen Threadripper 3970X running with a TDP of 140W in ECO mode delivering higher performance than the Intel Core i9-10980XE running with a TDP of 165W.
New features
Some new instruction set extensions: WBNOINVD, CLWB, RDPID, RDPRU, MCOMMIT. Each instruction uses its own CPUID bit.
On May 26, 2019, AMD announced six Zen 2-based desktop Ryzen processors. These included 6-core and 8-core variants in the Ryzen 5 and Ryzen 7 product lines, as well as a new Ryzen 9 line that includes the company's first 12-core and 16-core mainstream desktop processors. AMD's 2nd generation of Epyc processors, codenamed "Rome", features up to 64 cores and was launched on August 7, 2019.
