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LOSTCIRCUITS	SHORTCUTS: Dual Core vs HyperThreading Tech Specs Test Setup Memory Performance WorldBench5 3dsmax CineBench 2003 3D Gaming Power/Temperature Coefficient Power Hogs 3D Rendering Power DOOM3 3DMark2001SE 3DMark'05 Final Thoughts Give Us Some Feedback on this Review
AMD Athlon64 X2 "Toledo" Dual Core on Single Die
(Review by MS May 9, 2005)

Summary

Dual core CPUs are the latest buzz regardless of whether it is Intel or AMD. With the X2-series, AMD follows through on delivering two fully functional cores on a single die, connected internally by "direct connect" technology to take desktop computing to new heights. In theory everybody loves SMP, in practice, there are still questions about what goes beyond the lapidary statement "I am a multitasker, therefore I need SMP" that we have heard so often. What applications will really benefit from two cores, though? From a different perspective, what applications will see a performance hit? Keep in mind that the two cores only have one set of memory controllers, therefore the X2 characteristics may end up looking more like a Socket 754 processor in certain applications.

And then there was the issue of power, something that cannot be globally addressed by stating it is 2 x that of a single core unit. If all of that sounds strange, we have enough data to back it up. After 3 days of benchmarking and working basically around the clock to make this review happen, we have the good, the bad and there is very little that could be classified as ugly.

A lot of controversy has surrounded Intel's move to HyperThreading a few years ago, some applications did not see any performance increase, others actually were running slower but there were still those that showed a marked improvement. On the other hand, a single core is a single core and regardless of how many logical processors it is split into, the total power of the execution units will not change. What will change, though is the efficiency at which the core can access and, by extension, digest the data.

Beauty-Shot of the Dual Core AMD X2 processsor

Arguably, what works for one architecture may not necessarily be the all encompassing solution for the other architecture. Suffice it to say that as a rule of thumb multiple threads, running simultaneously as in the case of multimedia encoding, will experience more improvements than applications that are targeting single threads or even use the same resources for all threads running. Cases in point are 3D rendering programs such as Caligari TrueSpace or 3dsmax that may show logical processors in the form of independent scanlines, whereas the overall runtime is completely oblivious to the number of such units. The benchmark results will always be the same. No rules without exceptions, and the best known or publicized benchmark showing results to the contrary is Maxon's Cinebench 2003. In that case, HyperThreading makes a huge difference, at least for the raytracing.

The heart of the matter. What is interesting here is that the two cores are mirror-symmetric to each other, which arguably offers a number of advantages especially with respect to the shared memory controller units but from a design standpoint means a substantial extra effort since there is a right and a left "San Diego" core that needed to have the layout and verification done.

There is no doubt, though, that HyperThreading cannot be a true substitute for symmetric multiprocessing (SMP), which is one of the reasons why there is a sizable market for dual processor workstations. The main argument against dual CPU systems has been the complexity of the system itself, space requirements aside, there are power considerations, cooling bottlenecks, issues with cache coherency, shared buses, snooping, programmable interrupt controllers and last not least the fact that the home edition of the world's most popular operating system, namely WindowsXP does not support more than one physical processor.

From the very beginning, AMD's official party lines have condoned HyperThreading as rather unimportant marketing gimmick with the sideline of rather early revelation of the plans to advance the idea of SMP to bring into the desktop market what was reserved only for high-end servers, namely, two cores on a single chip. The result has been a project codenamed Toledo and Toledo has developed into a real product that is being released today as Athlon64 X2 in a number of different TPI (true performance initiative) ratings.

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