Articles: CPU

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The major differences of the new processors, which speed them up in common applications (and which you can actually feel quite easily), are larger L2 cache memory and high-performance integrated memory controller with low latency. These two innovations are the keys to increased performance of Athlon 64 and Athlon 64 FX processors.

If we regard the new AMD CPUs as a new enhanced version of AMD’s Athlon XP processor, there will be a few more things worth pointing out. AMD has long stopped increasing their CPU clock rates. The 0.13micron technology currently used in AMD’s fab30 in Dresden doesn’t allow the company to increase the CPU frequency over 2.2GHz for almost a year already. However, the actual performance of AMD CPUs keeps growing higher as the new processor models come out. The thing is that the processor actual performance depends not only on the core clock frequency, but also on the instructions the CPU is capable of processing per clock. AMD engineers have been working really hard on increasing the second parameter. During the last year L2 cache of AMD Athlon XP processors has already reached 512KB, and the bus frequency almost doubled. Of course, these changes affected the data and instructions transfer rate to the processor core, so that the number of instructions executed per clock has grown up quite noticeably in a number of applications. Athlon 64 and Athlon 64 FX represent one more step in this direction. Integrated memory controller and even larger 1MB L2 cache will allow speeding up the instructions feeding process even more, so that the idling of the execution units will drop down a lot. However, this is not everything yet. Fine-tuning of the used architecture, implying changes in the decoding algorithm, will also increase the processor core efficiency, because this way the CPU core will be able to processor more commands per clock. However, I have to stress right away that speeding up the commands decoder doesn’t have any serious effect on the processor performance in real applications. Firstly, it really works only in case of a pretty  limited instructions set, and secondly, the decoder acceleration we are talking about here is not that high at all.

As for the processor clock frequencies, things do not seem to be that comforting here. even though AMD uses a slightly improved 0.13micron SOI process to manufacture its Athlon 64 and Athlon 64 FX processors on AMD64 architecture, their core frequencies haven’t yet managed to exceed the 2.2GHz bar. The Athlon 64 FX-51 processor announced today works at 2.2GHz clock frequency, which is the same as that of Athlon XP 3200+, and Athlon 64 3200+ works at an even lower frequency: 2GHz. In the nearest future AMD is going to announce Athlon 64 3400+ with 2.2GHz frequency. As for higher frequencies, there is some hope that Athlon 64 FX processor model with 2.4Ghz core clock will be made with 0.13micron technology. After that AMD64 based CPUs should be able to acquire higher clock rates only after AMD moves to 90nm production technology and the new 64bit San Diego processor core comes out.

Now let’s try to figure out what are the differences between the mass Athlon 64 and the elite Athlon 64 FX for enthusiasts. In fact, the differences between them are not so numerous. AMD Athlon 64 is the CPU that AMD was going to launch a while a go already. Its major feature is the single-channel integrated memory controller supporting DDR400/DDR333 SDRAM. This is exactly the CPU that we managed to test about half a year ago (see our AMD Athlon 64 Performance Preview). Other than that this processor is just the same as other AMD64 based CPUs, except the Socket754, of course.

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