The original plan called for AMD to ship Athlon 64 in a single configuration. That configuration would support a 64-bit wide, single-channel, DDR333 memory controller. Given that the memory controller was integral to the Athlon 64 core, AMD thought performance would be pretty damned good. The speed of the memory controller would make up for any perceived deficiencies caused by the use of a single DDR memory channel.
However, AMD had to push the launch date back nearly nine months. Some of that delay may have been manufacturing issues, but some of the delay was the result of competitive pressures. Intel’s announcement of dual-channel DDR support, coupled with 800MHz FSB Pentium4s opened up a considerable performance gap between the Athlon XP and Pentium4 processors. While AMD continued to have an excellent price/performance solution, the P4 was cleaning up on the majority of benchmarks when comparing CPUs that were meant to compete with each other. It also necessitated a rethinking of AMD’s processor numbering scheme.
Instead of a single type of Athlon 64, there will be two types. One is the mainstream Athlon 64 3200+. This is the original CPU that AMD envisioned, although the single 64-bit wide integrated memory controller now supports a single channel of DDR400 memory instead of DDR333. The 3200+ uses the more common unbuffered DDR memory, and the CPU core clocks at 2.0GHz. The high performance part is dubbed the Athlon 64 FX-51. In this model, AMD is moving away from the controversial product nomenclature that’s been their mainstay since the Athlon XP first shipped.
The Athlon 64 FX series is the first of a family of FX-series processors. The FX can be thought of as a cut-down Opteron. It sports many of the features of the Opteron, including a 128-bit wide memory controller on-die, a 940-pin package and the requirement to use registered (buffered) memory. A key difference from the Opteron is that the 128-bit memory controller on the Athlon 64 FX supports two channels of DDR400 memory, rather than DDR333. Also the Athlon 64 FX includes only a single, active non-coherent HyperTransport link, versus three HT links in Opteron chips (though Opteron 100 series chips have no coherent HT links either, and we suspect the Athlon 64 FX still has all three links in its silicon, with two disabled). The initial model Athlon 64 FX-51 clocks in at 2.2GHz, whereas Opteron chips currently top out at 2GHz. The FX CPU die consists of 105.9 million transistors, for an overall die size of 197 square millimeters.
Interestingly, future versions of the FX will be built into a 939 pin package, capable of supporting unbuffered DDR memory. The timeframe for these new parts is a bit vague, but likely to occur only after the desktop Hammer undergoes a process shrink to 90nm.
Built into both Athlon 64 variants are 128KB of L1 cache and a whopping 1MB of L2 cache. The cache uses an exclusive caching policy, meaning that data in the L1 cache isn’t replicated in the L2 cache.