With that in mind let’s consider that either 8:8:8:8 (RGBA) or 10:10:10:2 (FP10), and a 32-bit Z-buffer the backbuffer should take:
63.3 MB for 1080p and 4xMSAA
28.1 MB for 720p and 4xMSAA
and with 16:16:16:16 (FP16), the figures double.
So by next-gen we should have FP16 blending support and a much higher transistor density. If MS wanted to make things really easy for developers, they’d go with the 128MB of eDRAM. It shouldn’t take a leap of faith to think that won’t happen. They sure didn’t make it easy to even do 720p & 2xMSAA this gen. At this point, I would expect 60MB in order to fit 720p, 4xMSAA, FP16.
But with the whole idea of tiling and “forcing” developers to think about implementing it now, MS could easily be hardware-cost-conscious and go with only 30MB at the very least.
They’ll probably implement those variations on FP10 that was discussed briefly in the “HDR the Bungie Way” presentation (i.e. 6e4, 6e5 versus the current 7e3 for FP10), making FP16 seem moot. They may target those instead, and in that way, 30MB seems an “ok” compromise.
It’s a question of diminishing returns. Do we really need to support universal 1080p? Some developers are getting used to tiling now… So perhaps 1080p, 2xMSAA (including CSAA/CFAA, which do not take extra storage), FP10 would be a better storage target (~32MB). But that’s only considering a single RT.