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LOSTCIRCUITS
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| AMD Athlon64-X2-3800+ The Mancunian Candidate | |
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(Review by MS September 20, 2005) |
| AMD Athlon 64 3800+ (Venice) |
Summary
With the latest stepping of the dual processor series, AMD dishes up the Manchester core to set new standards in energy efficiency and price/performance ratio. Taking advantage of the proverbial excellent gaming and floating point performance and stripping the dual cores of 50% of their hard-earned cache in combination with a frequency sweetspot of 2.0 GHz results in a killer CPU at a reasonable price tag. Arguably, there are cheaper processors on the market, there are faster cores out there (as measured in clock frequency) and there are "the others" but after wrapping up this review, there is nothing out there that combines that many positive features as the Manchester running at 2.0 GHz, using the moniker X2-3800+.
Parallel processing is becoming more and more mainstream. Intel is doing it, AMD is doing it and whoever is left is basically left behind -- unless they are doing it as well. Conventional wisdom has it, though, that there is no such thing as a free lunch and dual cores come with a price. The extra investment is, as we have shown in a few earlier articles, not only a one time shot for the purchasing price, on the contrary, Intel's D-series sets new records in terms of heat dissipation and power consumption, resulting in a somewhat increased electrical bill that, arguably, can offset the heating bill during the colder seasons, but also increase the AC costs.
The X2-series introduced by AMD looks somewhat better in that respect. However, especially in comparison with the award-winning energy efficiency of the Venice core, the introductory offers of AMD's dual core architecture did not look so great either. On the other hand, high power consumption is not necessarily a must, since power management should be able to take care of most of the overhead. Unless there is really load on both cores, there is no reason to keep everything up and running at full bore.
The wafer in the background actually contains "Toledo" dies, characterized by the large L2 cache.
Then there was the issue with the cache and its burning of energy. SRAMs are using power and fast SRAMs gobbling power for breakfast. The role of the SRAM-based L2 cache in power consumption is probably best illustrated in our comparisons of the Clawhammer vs. Newcastle cores running at the same core speed, which shows almost 25% reduction in overall power consumption after throwing out half of the L2 cache.
When we were looking at the Toledo, therefore, it was not overly surprising to see the power consumption shooting up way beyond that of two hypothetical Venice cores at the same speed, the extra cache on each "hemi" alone would account for that already. The San Diego core exemplified in the FX57, on the other hand churned out even more than half of the Toledo-based 4800+, however, bear in mind that the numbers we have reflect a core speed of over 2.8 real GHz, which makes the power consumption shoot through the roof by default.
Given the above, the strategy for a low power - high performance CPU would, therefore, have to be to use an existing design of the Manchester core with 512 kB L2 cache per "hemi" and throttle down the clock speed until a sweet spot is reached. The sweet spot in this case encompasses low voltage operation as well. A case in point is the Mancunian candidate we have on the test bench today, codenamed X2-3800+ and running at 1.3V, good enough to keep 2,000 MHz core-speed alive and kicking. The only question is, how good is the power / performance ratio really?
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Athlon64 X2-3800+ (dual core) |
next page: => X-2 3800+ by numbers =>
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