Out with the old, in with the new:
AMD’s new 65-nanometre processors are all labelled ‘Energy Efficient’, as AMD has managed to lower the maximum thermal design power (TDP) to 65W on all of the new CPUs. This is mainly thanks to the smaller design process, which has helped to reduce the voltage requirements down to between 1.25V and 1.35V.
In the past, AMD has only used integer values for the multiplier on its Athlon 64 processors and there were two different cache sizes throughout its line up. Back in June though, AMD stated that it would simplify its product line, retiring all dual core processors (except the Athlon 64 FX) that came with 1MB of L2 cache per core. The processors removed from AMD’s product range included the X2 4800+, X2 4400+ and X2 4000+.
However, AMD quietly re-introduced a couple of higher-end Athlon 64 X2s with 1MB of L2 cache per core; namely an X2 5200+ (running at 2.6GHz) and an X2 5600+ (running at 2.8GHz, the same clock speed as the company’s flagship Athlon 64 FX-62). Just to confuse matters a little more, AMD also introduced an X2 5400+ that is also clocked at 2.8GHz, although the difference here is that it only has 2x512KB of L2 cache. All of these processors are still based on AMD’s 90nm cores, though – the new 65nm Brisbane chips fit into the middle of AMD’s product stack.
Interestingly, the new processors based on the Brisbane core makes use of half multipliers (and all come with 2x512KB of L2 cache), meaning that we now see 100MHz speed grades in AMD’s product line. This change in strategy also sees the re-introduction of the three model names that AMD retired from its line up in June – X2 4800+, X2 4400+ and X2 4000+ are back.
Currently, the fastest Brisbane processor is the X2 5000+ EE that comes clocked at 2.6GHz – the chip AMD has sent to us – and, aside from the process shrink, performance should be very similar to the 90nm X2 5000+ based on the Windsor core. The X2 4800+ EE, X2 4400+ EE and X2 4000+ EE will present a different set of performance characteristics to the processors that they’ve replaced.
The other thing to consider is the way that AMD’s memory controller derives its memory speed, because it is unable to derive a memory clock from a half multiplier; instead, it uses the next full multiplier value to calculate the memory frequency. We touched on this during our first look at AMD’s socket AM2 processors, but this needs to be expanded upon here, because it could potentially confuse a few people.
Because the X2 5000+ EE shares the same characteristics as the 90nm X2 5000+ that it’s destined to replace, the memory clock is derived using the CPU/7 memory divider because it can never exceed the DDR2 speed set in your motherboard BIOS. Thus, the memory runs at 742MHz DDR on the X2 5000+ EE. Things get a little more complicated with the X2 4800+ EE, X2 4400+ EE and X2 4000+ EE, because they all use half multipliers to derive their internal CPU clock frequency.
The X2 4800+ EE cannot use the CPU/6 memory divider, because it would result in an 833MHz memory bus speed – that’s obviously higher than the maximum DDR2-800 frequency. As a result of this, the Athlon 64 X2 4800+ EE has to use the same memory divider as the X2 5000+ EE, albeit with a lower base CPU clock. This means that the memory runs at 714MHz on the X2 4800+ EE. The confusion continues with both the X2 4400+ EE and X2 4000+ EE, as both of these chips are forced to use the CPU/6 multiplier when the maximum memory clock is set to DDR2-800 in the BIOS. The resultant memory clocks are 766MHz on the X2 4400+ EE and 700MHz on the X2 4000+ EE.
Even though some of these memory frequencies are appreciably lower than the DDR2-800 you’ve selected in the BIOS, we still recommend buying DDR2-800 memory if you’re planning to get the most out of one of these new Energy Efficient Athlon 64 X2s. Things get a little more complex when you reduce the maximum memory clock in the BIOS to 667MHz, 533MHz or 400MHz. We’ll not bore you with the details here though.