AMD suggests Deneb will be the first processor on the new AM3 socket. Previous AMD documentation indicated that AM2 and AM3 would be forward/backward compatible — yet AMD engineers claim the AM3 alluded to in 2006 is not the same AM3 referenced in the 2008 launch schedule.
“At the time AM3 was the likely candidate to become AM2+,” claimed one field application engineer familiar with AMD’s socket migration. “[AMD] wanted to keep the socket name associated with DDR2 memory and backwards compatibility, but AM3 emphasizes DDR3 support.”
In other words, AM3 is not AM3.
In case you hadn’t been following this, AMD was supposed to have three sockets: AM2, AM2+, and AM3, (except when they felt like calling AM3 AM2+ instead, (I am not making this up.). AM and AM2+ CPU/mobos were supposed to be interchangable. AM3 CPUs were supposed to run (with some bells and whistles missing) on AM2 mobos, but not the other way around.
And what has changed now? While there are other changes between the various formats, the difference to key on is DDR2/DDR3 support and whether any future processors will support both.
The earlier statements seemed to imply that the Barcelona generation of processors would support both memory standards.
I think AMD was trying to imply or at least prepare the ground for one or both of two things with their statement:
1) The Barcelona-generation processors are “really” AM2+ processors which will not have DDR3 support and thus will not work in AM3 motherboards. You see, if Barcelona really “isn’t” an AM3 chip, then by AMD’s earlier guidance, it’s not supposed to run on AM3 boards.
I’m pretty sure about this one (and I suspect that when they did the “AM3 aka AM2+” last July, they had just this contingency in mind).
2) When “real” AM3 processors show up, they won’t support DDR2.
The second is reading tea leaves, and seems to be contradictory to what they literally said, but consider the following:
The memory controller chews up a significant chunk of die real estate. The one thing AMD isn’t going to have the next couple years is a lot of die capacity to spare, especially in 2008 with the delayed rehab of Fab30. Remember, this is the company that cut back on cache memory last year just to make more CPUs.
If they haven’t already decided it, it’s inevitable that two memory controllers on one CPU is a luxury AMD is not going to be able to afford, so out it will go, and someday, they’ll tell you.
Given all this, I think it’s safe to say that if you want to buy a Barcelona-generation CPU later this year, don’t count on it supporting a 45nm CPU, just as anybody buying a Penryn knows that it won’t support a Nehalem.
Yes, it is possible that AMD might make two separate lines of 45nm processors, one supporting DDR2, the other DDR3, with the first running on AM2+ boards, but until they tell you that, again, don’t count on it.