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Desktop performance?
If Clarksfield is really just Lynnfield squeezed into a notebook-friendly package, how does the mobile variant's performance compare to that of its desktop counterpart? That's a tricky question to answer given the unavoidable differences in clock speeds, especially when bolstered by Turbo Boost. Still, I ran a few benchmarks on a Clarksfield-based Clevo W870CU notebook with a Core i7-920XM and compared the results to some desktop performance data gleaned from our P55 chipset review to see what's what.

The Core i7-920XM runs a little behind the desktop competition in the Stream memory bandwidth benchmark, but that's to be expected given differences in the test systems used. Although the i7-920XM and i5-750 are both running dual-channel memory at 1333MHz, the desktop rig is using considerably tighter timings. I suspect that the i5-750 may also have a higher uncore speed than the mobile chip, but Intel isn't disclosing uncore speeds for mobile Core i7s.

Our desktop Core i7 system is only running its memory at 1066MHz because we used an engineering sample CPU that doesn't support 1333MHz memory. Bloomfield's third memory channel makes up most of the difference, but it doesn't help when we look at memory access latencies.

Here Clarksfield and Lynnfield are evenly matched, with just a nanosecond separating the two.

So what about application performance?

The i7-920XM actually has an edge over the Core i5 in 7-Zip, almost certainly because the latter lacks Hyper-Threading and is thus limited to executing four threads in parallel. All members of the mobile Core i7 family support Hyper-Threading, and 7-Zip is more than happy to take advantage.

Of course, the i7-920 is considerably faster than its XM cousin here. Both support Hyper-Threading, but the desktop chip has triple-channel memory and higher clock speeds on its side.

The first pass in our x264 encoding test doesn't make effective use of more than four cores, putting the i7-920XM well behind the others due to its clock speed disadvantage. However, the second pass is more effectively multithreaded, allowing our Clarksfield sample to pull up just a few frames per second short of the faster four-thread Lynnfield CPU.

Additional threads and memory channels appear to have little impact on performance when executing stitch operations with The Panorama Factory, as evidenced by the close performance of our two desktop parts. The Core i7-920XM lags behind by a fair margin here, no doubt due to its lower base clock rate.