You should be asking
chris 1515 in my opinion. My novice take is that they have a complete pipeline for RT thanks to the Caustic legacy. They've been making hardware RT for almost a
decade at this point, and John Carmack
thought their tech half a decade ago was solid.
I think there are two possibilities. One is that they always conceived of pushing out a non-final APU for developers to play with. This could be an off the shelf Zen 2, IO, and Navi dies, with potentially only changes to the IO die needed. Additionally, it could be pin compatible with the final product. This would enable PS5-like silicon in their hands up to a year before they get the real development chips.
As a thought experiment - why does Navi 12 exist? A Navi 10 like design with hardware updates and HBM memory. Who is the desktop consumer for a product with high memory cost? Unless the memory cost isn't actually that high anymore, the product is simply a leveraged version of something used
elsewhere, or both.
The second possibility is that this is plan B. At some point in early 2018 (At the latest), they called an audible and decided that Navi 10 wasn't good enough. Could this be a reaction to what they thought MS was cooking, how the narrative of X vs. Pro was evolving, developer feedback (this would have been the time Cerny was touring developers), or AMD pulling some roadmap items in as they went through some tumultuous times? Who knows. Small snippets like Chinese forum posters alleging a hardware revision would cut it close for 2020 launch are potential clues, though I am hesitant to bite on those things too hard.
What I do know is that virtually every insider is saying PS5 and XSX are close, and most of those are sticking to that story after the XSX reveal. We know hardware RT is confirmed. Sony said it,
Matt said it,
Kleegamefan said it. One of our grandmothers probably said it. Klee has also said VRS is included, and everyone is suggesting >10TF. All of these things Navi 10 is not. It would be surprising to see this many people with other valid info turn up wrong on this.
And to make my lack of allegiances clear - I am team parity. I own Pro and X and love them both.
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