Today's launch is as much about AMD's new FX-70 series processors as it is about the rest of QuadFX platform as a whole. In addition to a pair of FX-70 series processors, QuadFX requires a dual-socket motherboard to accommodate the two processors. Although AMD recently acquired ATI and all of their chipset assets and IP, they have chosen to launch the QuadFX platform with a chipset built by NVIDIA. All initial QuadFX systems will be powered by the nForce 680a SLI chipset. The high-level block diagram below outlines the interconnects and main features of QuadFX.
As you can see, each dual-core FX processor is linked to its own banks of DDR2 RAM, and the processors themselves are linked with a coherent HyperTransport bus. Only one of the CPU sockets is directly connected to the nForce 680a chipset via a pair of HyperTransport links, however. This was done to make it possible to use QuadFX motherboards in single CPU configurations. We should note that all of the HyperTransport links on the board are full 16-bit links, operating at 1GHz (2GHz DDR).
As of today, the QuadFX platform allows for two, dual-core processors to be installed, for a total of four execution cores in a single system. In the future though, when AMD has native quad-core processors in their product line-up, QuadFX will scale to an 8-core platform. And technically, since AMD opened up their Opteron architecture with their Torenzza initiative, that second socket doesn't have to contain a traditional x86 CPU at all. Instead, specialized co-processors can be installed in the second socket that interface with the system via HyperTransport. It's going to be interesting to see what the future brings to QuadFX.
This "quad-core" setup is obviously much different than Intel's. Whereas Kentsfield-based processors are a multi-chip package with two, dual-core dies on a single chip, QuadFX is a pair of dual-core processors linked via serial interface. Intel's current solution is much more cost efficient, and more elegant in our opinion, but the AMD architecture has a major advantage, namely the coherent HT link between the processors. For any communication via the individual cores, Kentsfield has to send data off one die, over the FSB, and back to the other die. A pair of Athlon 64 FX-70 series processors can communicate directly over a dedicated HT link without contention over a shared front side bus.
Having two independent processors though, each with their own memory controller, means QuadFX has a non-uniform memory access, or NUMA. The system can be configured as two independent nodes or with node interleaving, but the operating system being used has to have proper support for NUMA because the way the OS accesses system memory can have a major impact on performance. For example, Windows XP doesn't properly support NUMA due to the way its scheduler loads execution cores in a multi-processor system. With XP a single thread could bounce from core to core. Windows Vista does properly support NUMA, however, and Vista's scheduler shouldn't shift single tasks between individual cores. As you'll see later (on our SANDRA and PCMark05 pages specifically), there is a large difference in available memory bandwidth when the OS has native NUMA support.
Also note the impressive list of features brought forth by the nForce 680a SLI chipset. The 680a is a multi-chip solutions that is derived from NVIDIA's nForce Professional 3000 family of products. As such, the chipset has support for up to 56 PCI Express lanes, 4 Ethernet MACs, 12 SATA ports, HD Audio, Firewire, and 20 USB 2.0 ports. The block diagram above shows one configuration with four PCI Express x16 slots, which would support quad graphics cards, but the PCI Express lane configuration is flexible should other motherboard partners eventually decided to outfit their upcoming QuadFX boards in a different manner. The 680a SLI has a slew of other unique features as well, like FirstPacket and DualNet, for example. We go into detail regarding the nForce 600 chipset family's features in this article.