Core i5 - any degradation from 2-channel memory?

[WyomingKnott]

Core i7 had three-channel memory, but nothing like a 50% edge over Core Duo in memory bandwidth.

When Core i5 comes with two-channel memory, do you think that it will have significantly worse memory throughput than the three-channel versions (which would put it below Core Duo), or will it turn out that the third channel has very little effect?

I've been waiting to see what Lynnfield can do before building a new machine. The TDP difference between the i7 and the expected TDP for the i5 is so large that I'd rather wait for the i5. But will two-thirds the memory channels have a major effect or not?

Until these are benchmarked I ask, what do you expect? Also, I don't know of any benchmarks comparing two-channel to three-channel; can you point any out to me?

Thanks.

 

[j-g-faustus]

According to Tom's Hardware:
Performance loss triple -> dual channel avg. 0.6%, triple -> single channel avg. -2.1%:
http://www.tomshardware.com/reviews/Intel-Core-i7-Nehalem,2057-13.html

A difference, but hardly a massive one.

 

[JAYDEEJOHN]

In almost all current DT apps, youll see no gain from tri channel. As to the power usage, the TDPs are 35 watt different, or 130 vs 95

 

[cjl]

As far as memory bandwidth is concerned though, you're wrong about the first statement. i7 has more than double the memory bandwidth of the best Core 2 Duo setups (or core 2 quad), and memory bandwidth scales pretty much linearly with channels for a given controller. I would expect the dual channel i5 to have pretty close to exactly 2/3 of the bandwidth of the i7 with the same memory, but I wouldn't expect it to have much effect on actual performance of programs.

 

[j-g-faustus]

While on the subject of memory:
The Tom's Hardware test on DDR-800 vs DDR-1600 shows about the same - having twice as fast memory almost doubles memory bandwidth, as expected, but with a couple of exceptions this is hardly noticeable for most applications:
http://www.tomshardware.co.uk/memory-scaling-i7,review-31600-10.html

I guess this means that on modern hardware very few desktop applications (including games and video encoding) are limited by memory bandwidth.

I would imagine memory bandwidth becomes more important if you are running something like a web server?

 

[JAYDEEJOHN]

Primarily, thats where BW shines, in server apps. i7 is basically a server cpu, that does well on DT, as did/does any AMD since the addition of IMC on their cpus, which Intels now doing on i7, and on i5 as well, the main difference being tri channel vs dual, whch only opens up BW even more using tri channel, but woefully uneeded on DT

 

[WyomingKnott]

Thank you all for the input. The key piece of information for me is that the lesser memory bandwidth does not have a major impact on application performance, although it does have a measurable one.
TDP may be my deciding factor - I want a quiet machine in my home office. It's also the warmest room in my house (why I was allowed to have it!), and the less heat thrown the better.
Strangely, the main reason I want a new machine at all is to play with benchmarking RAID arrays.