Do 667MHz SODIMMs cause a performance bottleneck for Santa Rosa?

[dhavleakx]

I'm basically trying to understand what the 800MHz FSB in Santa Rosa means from a performance standpoint.


In all the Santa Rosa specs I've seen, the Santa Rosa CPUs support an 800MHz FSB. My understanding is that this means the CPU to PM965/GM965 bus operates at 800MHz.

AFAIK, the memory controller in Santa Rosa lives on the chipset (PM/GM965). This operates at 667MHz which is the same as the previous generation. i.e. the memory bandwidth between Santa Rosa (SR) and the previous Centrino platform is the same. Indeed, specs for all SR laptops released so far show that the fastest memory they will use is DDR2 667MHz (they might accept faster memory - but they will operate it at this speed).

i.e. even once 800MHz DDR2 SODIMMs become available, there is nothing to be gained by upgrading your memory since the 965 chipset will only talk to it at 667MHz (overclocking etc. aside).

Which is basically is the meat of my question: if the memory bandwidth of the platform has remained unchanged then should I expect to see a performance jump from this platform refresh? I think of this as an important question, because from the early indications so far, it looks like the power savings from SR can be considered somewhat intangible compared to the previous generation. If that's the case, and if the memory bandwidth parity with previous generation implies similar performance, then does it make sense to:
- buy a previous generation centrino laptop if purchasing immediately (save cash)
- wait a few months until there is a chipset with an 800MHz memory controller which can maximize SR performance?

Thanks for your responses!

ps: I would appreciate it if overclocking could be left out -- I'm more concerned about spec-ing a stock laptop from say, dell or lenovo and making sure i'm made all the optimum choices.

 

[cprince]

I think that you should buy previous generation to save money. I don't think that there is a big performance different between 800MHz and 667MHz memory controller. This is especially true for laptop because, chances are, you will not run applications that need a lot of memory bandwidth like games on your laptop.

 

[Idontcare]

Well not sure if this answers your question - but hopefully it adds some value - checkout the bandwidth table in this AT article P35. Look at the first row, second column 5754 MB/s for 1066 FSB versus 6456 MB/s for 1333 FSB...all with memory at 800MHz DDR2...in other what benefit is there for solely increasing the FSB and not the memory speed (which I beleive was basically your question). Here you can see a measurable difference in synthetic benchmark.

Whether the value of the measured differences is enough to justify the cost structure is up to the consumer. For the remainder of these preliminary benchmarks in the AT article is does not appear to create much value add to increase FSB while holding memory speed constant.

 

[dhavleakx]

Thanks for the link to that article. It does answer my question to some extent.

What I inferred is that since the SR processors don't have a significantly higher IPC (instructions per clock cycle) than their predecessors then the bus speed is not going to make a significant impact for most apps. That does explain the mere 2 to 3% performance improvements that have been reported so far (though admittedly nobody seems to have done proper apples:apples benchmarking yet).

This is a little disappointing

 

[Noubourne]

Maybe you misunderstand Santa Rosa in the first place.

It isn't about improving performance as much as it is about improving battery life. This is a mobile platform, and it takes the exact same CPU (C2D Merom) as Napa took. It has an 800mhz FSB, but as mentioned already, only takes RAM up to 667, so that extra bandwidth is likely wasted, even when it happens to be turned on.

Certainly not worth the price premium unless you're that much more of a stickler for battery life, b/c most of the Santa Rosa improvements are aimed at extending battery life.