I think will not support Win7 and lower due to new instruction set, having to do with the SMP (Simultaneous Multi-threading Processor) instructions Zen is using.
I might be wrong, but I think Kaby Lake will have the same "limitation".
I doubt very much that it has anything to do with SMP. Every CPU from Dual-Core upwards is an SMP architecture.
It seems that both AMD with Zen and Intel with Kaby Lake have agreed to make their CPU's incompatible with Windows 7. Microsoft tried this stunt with Intel's Skylake but the protests about this forced Intel to back down.
I do not think it is a wise move on the part of AMD to give a one finger salute to over 50% of Windows users (that's just the Win7 users), especially considering that the sale of desktop PC's has been flattening off or even stagnating in recent years.
From what information I have been able to glean the incompatibility between Zen and Win 7 is completely artificial.
Personally I will not be forced onto an OS platform which in my experience has been glitchy, subject to crashes and also unpredictable. I build computers to run 24/7 for years and even on the Haswell and the AMD APU platforms I have not been able to get Windows 10 running for HOURS let alone days or weeks, without some kind of either crash or BSOD which I just do not experience with Win7. I put a link to my AMD computer above and there is absolutely NOTHING second rate or inherently unstable in that build.
My previous main rig had been running 24/7 for 1,790 days before I changed over to the Haswell platform.
I was very much looking forward to the new Zen APU's but as of this writing, if Win 7 is not supported then there is no chance of my buying it.
I found a quote from AMD chief technical officer Mark Papermaster which stated. “AMD’s processor roadmap is fully aligned with Microsoft’s software strategy”. What this says to me is that AMD is being dictated to by Microsoft, to try to force people onto Windows 10 which is widely seen as an abominable OS.
What this means is that AMD will be pandering to 33% of Windows users and telling the other 66% to get stuffed.
I do not see this boding well for AMD's launch of Zen or their sales.
This is the problem of closed source software products like MS Windows. If the owner/seller/vendor (MS) dont want to add support for new CPUs/technology on old OS releases you cant do anything about it, except vote with your wallet (money) and change to an opensource OS were support for new technology will be added.
Please send your complaint to Microsoft, Windows is their product. I see this all the time on healthcare software/hardware.