It’s in the Fine Print
The first things one looks at in comparing chips from the same family are price and clock, and indeed we did that in the first article. There are other very important things to consider, though. Intel buyers are used to seeing which instruction sets are supported and how big the caches are to help them make buying decisions, and for i7 these are the same in all three chips.
What might sneak up on them is that two of the big new features of the Core architecture, QPI and the on CPU memory controller, are implemented at different speeds on the different CPUs. The Quick Path Interconnect runs at full speed (6.4 GT/s) on the top-end 965 XE, but the 920 and 940 run at 4.8 GT/s.
This didn’t have a significant effect on overall performance in the myriad tests we found published. Plus, next year’s Ibex Peak platform for mainstream and performance Core CPUs will use the much slower Digital Media Interface instead of QPI, so the difference between the low and high QPI speeds almost certainly isn’t an issue. We have more on Ibex Peak in the next article.
The different memory controller speeds, however, do impact performance; not tremendously, but notably. The 965XE will run memory up to 1600 MHz , while the 920 and 940 can only handle 1066.