AMD has released details of its next-generation desktop CPU interface, Socket AM3, to its OEM
partners. In a mildly surprising move, AMD has revealed that AM2 will
accept AM2 or AM3 (also dubbed AM2+) CPU packages. Additionally, recent roadmaps have
confirmed that AM3, AMD's upcoming desktop CPU socket, will not be backwards compatible
with AM2-package CPUs. Roadmaps and memos have also confirmed that this
AM3 package will be for AMD's
"K8L" architecture, and not for the upcoming 65nm AM2 Brisbane CPUs
scheduled for launch this December.
The most recent AMD roadmap is also very clear to state AM3 "supports either
DDR2 SDRAM or DDR3 SDRAM, but not on the same motherboard." This is
great news for upgraders, as there is a very clear upgrade path: CPU,
motherboard, and then memory. This also infers that AM3 CPUs will have
both DDR2 and DDR3 support on the integrated memory controller. DDR3, like DDR2, has 240-pin, but the two formats are not pin-compatible.
As we also mentioned earlier, Greyhound will be
the first desktop processor to support HyperTransport 3.0. Part
of the specification for HT-3 is backwards compatibility with older revisions
of HyperTransport, and the forward compatibility of the AM2 socket confirms
that. However, it’s important to mention that even though AM3 CPUs will
work in the AM2 socket, HT-3 allows for 5.2 Giga-transfers per second, while
current AM2 motherboards top out at 2.0 Giga-transfers per second. Even
though the additional headroom is likely not completely necessary, quad-core
CPUs will certainly benefit from the additional bandwidth to additional CPUs or co-processors.
There is no word yet on the number of pins the new socket will require, but
since AM2 sockets are forward compatible with AM3 CPUs, we can at least
deduct that AM3 will have fewer than 940 pins. Furthermore, since
Socket AM2 is forwards compatible with AM3 CPUs, it is also safe to say that
AM3 is not a land-grid array (LGA) socket. AMD will switch its Opteron
platform to an LGA-1207
socket on August 1, 2006. AMD has not announced when Socket AM3 will be released, although since it would be the first HT-3 "ready" socket design, it seems likely that K8L and AM3 for the desktop will launch simultaneously.