AMD Quad FX: Closer Look

CPUs

Note that Quad FX doesn’t really strike us with its intellectual design when we cast the very first glance at the CPUs that AMD intends on using in this platform. And here is why we think so. The current K8 micro-architecture AMD is using these days allows assembling multi-processor configurations very easily. One of the things that make it easy is the three HyperTransport busses in AMD processor cores. Nevertheless, the Socket AM2 infrastructure that appeared in the market about half a year ago turned out absolutely unprepared for the multi-processor configurations. This 940-pin processor socket has contacts for only one HyperTransport bus, which is surely not enough even for a dual-CPU configuration. Therefore, only a few months down the road from the Socket AM2 desktop processors launch, AMD had to start promoting a new socket for desktop Quad FX platforms.

Since there was not that much time available, AMD didn’t design an absolutely new processor socket this time. For the new Quad FX platform concept they decided to go with the 1207-pin Socket F that is moreover designed in LGA form-factor. Sockets like that are used in contemporary server systems for AMD Opteron CPUs and Registered DDR2 SDRAM.

I have to admit that the use of Registered DDR2 memory wouldn’t be the best decision AMD could make for its desktop platforms. Although Registered memory is much more stable, it is also more expensive than the regular DDR2 SDRAM and features higher latencies. Therefore, AMD decided to replace the memory interface in the Quad FX systems: these CPUs use regular Unbuffered DDR2 SDRAM. As a result, Quad FX systems also lost their connection with the server infrastructure.

Taking into account everything I have just mentioned above, AMD had to create a few absolutely new dual-core processors that are not compatible with any platform other than Quad FX. They were formally placed within the Athlon FX processor family. Just like the today’s Athlon 64 FX for Socket AM2, these processors are based on 90nm Windsor core, however they boast three active HyperTrasnport connections, one of which serves to connect the CPUs with one another.

Today AMD is offering three models of dual-core Socket 1207 processors that are compatible with the Quad FX platform. They are Athlon 64 FX-70 working at 2.6GHz clock speed, Athlon 64 FX-72 working at 2.8GHz and Athlon 64 FX-74 working at 3.0GHz. They will launch one more faster processor in Q2 2007: AMD Athlon 64 FX-76 with 3.2GHz clock speed. All these CPUs feature 2MB total L2 cache memory shared between the cores. The detailed CPU specifications for the AMD Quad FX platform look as follows:

• Processor core: dual-core Windsor;
• L1 cache: 128KB per core (64KB for data and 64KB for instructions);
• L2 cache: 1MB per core exclusive cache;
• HyperTransport bus: three 16bit/16bit busses working at 2000MHz;
• Memory: integrated dual-channel DDR2 SDRAM controller supporting Unbuffered DDR2-800/667/533 SDRAM;
• Packaging: 1207-pin LGA;
• Production process: 90nm, Silicon-on-Insulator, Dual Stress Liner;
• Die size: 235sq.mm;
• Transistors: ~227 million.

And this is the currently available product line-up:

Note that the above listed CPUs are sold only in pairs, so you cannot purchase a system with only one dual-core CPU intending to upgrade in the future.

Two Athlon 64 FX-74 processors we got in our lab

As we see, AMD is trying to create analogies between its new Quad FX platform and the quad-core competitor’s solutions. However, from the compatibility standpoint the new AMD platform looks less attractive than Kentsfield. It can be called “a thing in itself? unfortunately, it is not compatible with any other platforms and requires only special dual-core CPUs.

However, AMD do their best to present this fact from an advantageous standpoint. They claim that Quad FX will not be just a temporary solution temporarily making up for the absence of quad-core processors in the company’s product range. AMD promises this platform will live much longer. Moreover, when the quad-core processors also known as Agena (former Altair) are ready, they will be also adopted by the Quad FX platform. In other words, AMD is introducing Quad FX as a new innovative platform for computer enthusiasts who want to get the maximum performance at any price. Today this platform provides four simultaneous computational threads, but in the second half of 2007 it may be enhanced to be able to process up to 8 parallel computational threads.

By setting special prices for the CPU kits AMD managed to get the total cost of the new Quad FX platform very close to that of the Intel Kentsfield based systems. However, from the today’s popular performance-per-watt viewpoint, the situation is not that rosy at all. Athlon 64 FX processors for Quad FX platform manufactured with 90nm technology feature typical heat dissipation of 125W each. As a result, two CPUs like that will consume almost twice as much power as the top of the line quad-core Intel processor. So, from the efficiency standpoint, the new AMD Quad FX platform is losing to the Intel competitor big time. As for the performance leadership, our test session will reveal, who the winner is shortly.