I agree. It seems like a fairly substantial jump.
But here's my theory
- The IOD for Zen3 could possibly be fabbed by TSMC going forward. This could explain the jump in needed wafers because the IOD is not small.
- Assuming worse density scaling than the CCDs because of the PHYs and IOs it will be bigger than the CCDs (80-100mm2 DT and 250-280mm2 EPYC)
- This is bound to happen at some point. I am not sure GF can make the super dense micro bumps needed in the future for die stacking.
- The cores and cache grew in size for Zen3
- Zen --> Zen2 core saw a growth of ~36% in transistor count including L3 cache. Just the core with the L2 it grew 17%
- An increase in the CCD die size of 15% lets say means AMD would need 15% more wafers even keeping demand at same pace. And yield would drop even more.
- Additional wafer allocation for Q4 could be needed to cover additional products for Cezanne/Mobile APU. We know AMD has to be in time for OEM refresh otherwise they will miss the bus.
I don’t know if the chiplet die size will increase much at all over Zen 2. Zen 2 already has 32 MB cache per CCD (2 x 16 MB CCX) and the same number of cores. In Zen 3, it will all be unified into a single 8-core CCX, but it is still the same number of cores and L3 cache. It may be larger L2 size and the new architecture will take more transistors. Floating point hardware takes a lot of die area and there is a good chance Zen 3 has significantly increased FP power. I don’t know if they will go up to a full 4 AVX256 units. Some of the transistor count increase may be offset by denser process. Die size increase probably will not be due to L3 cache though, since it is actually the same amount per die. A larger cache size product may exists in some manner. That may be what the specialized super computer chips are. They could also possibly do something like Intel does (differing number of AVX512 units) and have a chip with more FP units. That gets complicated due to scheduler ports though. Initial Zen 1 was one die to do everything but AMD has a bit more money now, so they can afford to do more die variants to better cover the market.
I haven’t read this whole thread, so some stuff may have already been mentioned or debunked. I have ave been thinking that Zen 3, being a completely new architecture, will actually be very conservative in the initial release and use almost the same IO as Zen 2. Then Zen 4 will just be a shrink and/or slightly tweaked version of Zen 3, but with completely new IO die (pci-e 5, DDR5, etc). It may make sense for the Zen 4 EPYC IO die to be an interposer or just made of multiple chips. If they want to add L4 cache to the EPYC IO die for a more unified last level cache, then they would want to make them on a leading edge process for maximum density. It would also make sense to have them split into separate chips if they have a lot cache. Things get a bit crazy with an interposer or multi-chip IO die since there is a large number of possibilities.
I expected that the initial Zen 3 launch would be mostly EPYC and a small number of high end desktop parts. The Zen 2 XT parts are a bit confusing though. Are they going to release R9-4900 and R9-4950 in 6 months? I guess they may have just been getting high binning parts, so they decided to release some faster variants to look better against Intel and sell off some Zen 2 stock before Zen 3.
They could be working on a 5 nm APU based on Zen 3. If they have an 8 core single CCX Zen 3 APU, then would there be a reason to sell a single Zen 3 CCD + IO die for the low end desktop market? I guess I could see them making a 2 die APU also, with cpu + IO on one die and a small GPU die. That would allow for maximum flexibility, especially if they make a GPU die with an HBM stack.