AMD Athlon 64 3800+ and FX-53: The First 939 CPUs

Introduction

The past year has been quite a ride. With the introduction of the Opteron, and later the Athlon 64, AMD has proven that it can stretch beyond just designing processors. As much as the original K7 architecture was a solid processor, AMD have really done something special with the Athlon 64 architecture. Creating a chip that performs well in current systems while taking a step past Intel into x86-64 support is no small feat.

Of course, that's not to say that everything has gone smoothly for AMD. Opteron and Athlon 64 were delayed before their initial release, and we didn't see parts until much later than we had expected. When the parts finally arrived, they performed very well, but the overclocking that AMD had been known for in the Athlon XP line was definitely lacking. To top it off, Athlon 64 was released with a single channel memory controller while it's big brother the Opteron had dual channel support (which is perceivably part of the reason the part was so much faster than the Athlon 64 line).

As a result, almost since its launch, enthusiasts have been waiting for Socket 939 to bring dual channel memory to the Athlon 64 line. In addition, the chipsets that will be powering 939 pin motherboards will be capable of a 1GHz Hypertransport bus (with PCI locks) hopefully giving them a little more stability and overclockability than the original Athlon 64 line had. On the desktop side, in the interim, we saw 512kB cache (cheaper mass market) revisions of the Athlon 64 bring us the 2800+ and 3000+ processors, which both performed very well for their price point. This worked well because the Athlon 64 isn't heavily pipelined and is less effected by cache than the Pentium 4 line of processors.

In addition to expanding into lower cost markets, AMD needed an ultra high end desktop part to show off its potential to the world. The FX-51 and FX-53 have really put AMD on top of the desktop market in terms of gaming performance, though these parts arguably don't have as much value (price to performance wise) as the cheaper but very highly performing Athlon 64 processors. Unfortunately, in order to introduce these enthusiast parts with dual channel memory very quickly, AMD essentially just tweaked and rebranded their opteron processor and made socket 940 another desktop platform.

Unfortunately, those who want the higher performing (and higher priced) FX processor also need to shell out more money for a higher end motherboard than needed and slower, more expensive, registered RAM. Moving to 939 will bring a single platform to the desktop and give users one less choice to have to make in their purchasing decisions.

One of the major issues with having multiple generations of processors with different memory controllers is that AMD has to be careful about not allowing CPUs with different memory controllers to fit into the sockets of unsupported motherboard. This means that every new generation of memory controller for AMD will bring a new socket to the market. Intel is able to be a little more agile in this area, as the memory controller is in the chipset. This is only an issue when bad decisions are made, such as when Intel decided to adopt RDRAM. They might not have been able to switch back over to DDR so quickly had they fabbed all their processors with a RAMBUS memory controller on the die.

So, today we are seeing the introduction of socket 939 for the AMD Athlon 64 and FX. The bottom line is that we are seeing the same VIA and NVIDIA chipset based motherboards with a different socket attached accepting processors with nothing new but a dual channel unbuffered memory controller. What exactly does this mean, and what kind of performance can we expect?