AMD Phoenix APU Uncovered: Zen 4 Meets RDNA 3

[harlan4096]

AMD's RDNA 3 heading into monstrous APU.

Yesterday's AMD RDNA 3 leak not only exposed three discrete Navi 30-series graphics processors based on the next-generation architecture but also revealed one integrated GPU. The integrated GPU will be used for an accelerated processing unit codenamed Phoenix, and this chip appears to pack quite a punch if unofficial information about it is correct.

AMD's codenamed Phoenix APU appears to be based on the company's upcoming Zen 4 microarchitecture, but the number of cores is unknown (we would speculate about eight Zen 4 cores, though we would keep in mind that AMD also has cut-down Zen 4c cores). The graphics part of the APU seems even more interesting as it uses the upcoming RDNA 3 architecture and may pack as many as 16 GPU compute units. In the case of RDNA 3, that translates into 1536 stream processors (today's APUs feature 512 SPs), according to ComputerBase, citing various unofficial sources. Of course, AMD won't talk about its Phoenix APU any time soon.

Phoenix could have a GPU offering performance akin to a current-generation discrete Radeon RX 6500 XT graphics chip, or perhaps even closer to the RX 6600, depending on what RDNA 3 brings to the table. Meanwhile, to provide enough memory bandwidth for such a monstrous integrated GPU, AMD intends to support DDR5 and LPDDR5. The APU is also said to support a PCIe 5.0 interface. Unfortunately for desktop gamers, AMD seemingly only plans to offer Phoenix for notebooks and perhaps compact or all-in-one desktops.

In recent years, AMD has packed its latest Zen CPU cores into its APUs to make them competitive in general-purpose workloads. However, the GPU part of those APUs was based on the Radeon RX Vega design, which uses a highly modified GCN (graphics core next) architecture from 2011. As a result, while these APUs are good enough for everyday workloads, they are barely adequate for gaming and media (because of outdated video decoding/encoding units and video processing engines).

With its upcoming Ryzen 6000-series 'Rembrandt,' AMD finally weds its up-to-date Zen 3+ cores with a contemporary RDNA 2-based GPU. However, the combination of Zen 4 and RDNA 3 featured by the future Phoenix APU seems even more appealing. The only question is when exactly this chip will become available.

Another question is which process technology (or technologies?) will be used to make AMD's Phoenix. AMD's Zen 4 cores are designed for TSMC's N5 node, whereas the company's RDNA 3 GPUs are rumored to use N5 and/or N6. Given AMD's focus on Zen, we are pretty sure that the Zen 4-based Phoenix will use N5, just like Raphael. Meanwhile, keeping in mind that AMD tends to re-use its GPU IP in APUs without many changes, we are less sure how things will play out there. Throwing an N5 GPU IP into an APU may not be feasible from a manufacturing costs perspective, whereas redesigning an N6 IP may be too expensive. Perhaps AMD will switch to a tiled design for its APUs, but that's pure speculation.
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