Apple may be converting its Mac products entirely over to its own SoCs, but the company evidently plans to use AMD’s GPU hardware for at least one more product cycle. Apple’s Big Sur 11.4 beta adds support for graphics cards based on the RDNA2 architecture, including the Radeon 6800, 6800 XT, and 6900 XT. The Apple note doesn’t mention the 6700 XT, but we’d assume that GPU will be supported as well.
Apple adding RDNA2 support is news because it hasn’t been clear if the company intended to support future discrete GPUs from AMD at all. Apple’s M1 includes its own GPU core and the company has already replaced some iMac options that previously shipped with a discrete GPU with an M1 SoC that does not. Thus far, the GPUs in question have been low-end cards based on the diminutive Polaris 21 architecture.
The Mac Pro line packs more serious firepower. While the system ships with a Radeon Pro 580X (aka Radeon RX 580) by default, it can be upgraded to the Radeon Pro Vega II or Vega II Duo, which features two Radeon VII dies side-by-side on the same GPU.
Apple’s M1 is an impressive SoC, but slapping a 4096-core GPU alongside it would be a bit much.
Apple could swap AMD hardware for Nvidia if it chose, but it can’t easily integrate a top-end GPU into a CPU socket. The Radeon Pro Vega II in the top-end Mac Pro features 32GB of HBM2, a 331mm sq die, and a 475W TDP. The M1 already features up to 16GB of on-package memory, but any HBM-equipped SoC intended to replace a workstation graphics card would have either a GDDR6-style bus connecting it to dedicated onboard VRAM (like a modern console) or a 16-32GB on-package HBM2 buffer.
There’s nothing stopping Apple from pursuing this kind of solution or building its own discrete GPUs, but either is a major undertaking. If Apple wants to replace Intel in the Mac Pro, it will need to build CPUs with 12+ high-performance cores. That’s an undertaking in and of itself, and Cupertino might decide to build high core count CPUs first before attempting to integrate enormous GPUs alongside them. Apple might also intend to build its own discrete cards for the Mac Pro, but not until it perfects its own architecture in integrated form first.
Apple hasn’t really talked about how it intends to handle its GPU transition or the degree to which it will support both Metal and RDNA2. It isn’t clear if Apple intends to replace its existing discrete GPUs with integrated SoCs more powerful than the Xbox Series X or PlayStation 5, continue to use AMD cards, build its own discrete GPUs, or pivot away from the high-end GPU market with future Mac Pros altogether, and offer more modest levels of GPU performance. Modest, in this context, means something more like a midrange dGPU with 4-8GB of on-package VRAM rather than a 32GB HBM monster with 4,000+ cores and a 250W+ TDP. Only Apple knows its long-term plans, and for now, the company isn’t sharing.
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