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Today's desktop replacements deliver a ridiculous amount of performance compared to the mobile flagships we've seen in the past. But these powerhouses come with a trade-off, other than their hefty price tags. You see, there is an unbreakable relationship between compute horsepower and power consumption.
On the desktop, processors based on Intel's Sandy Bridge architecture top out at 95 W. This is a significant improvement over the 130 W Bloomfield design, manufactured at 45 nm, since performance is higher in many cases. Nevertheless, it's still not realistic to use desktop-class CPUs in notebook shells and expect them to last very long on battery power. Then again, most of the folks who buy DTRs don't really care about keeping away from wall sockets. They're more interested in using those machines as workstations that transport easily from one power plug to the next. In that case, a larger form factor is fine and dandy.
To be fair, Bloomfield was never intended for notebooks. Neither was Lynnfield. The true first-generation Nehalem-based CPU aimed at the mobile space was Clarksfield. The second-generation that followed was Arrandale.
At the high end of the mobile space, Clarksfield kicks butt. You just need to take a peek under the hood of any DTR from a major system vendor. It is almost always a Clarksfield-based processor. There's a good reason behind this. Transitioning from the Core microarchitecture to Nehalem was a really big deal, both in terms of what it did for potential performance and power management. Truly, Nehalem-based mobile processors can go toe-to-toe with their desktop big brothers (if you don't believe us, read Thomas' coverage of the Clevo X1800).
Sandy Bridge Mobile: Core i7 At 55 W/45 W
Intel continues to use the Core i7, Core i5, and Core i3 brands, suggesting good, better, and best. While we're still not sure that this is superior to what it had going with Centrino (now the designator for the company's wireless radio), we'll admit that the trio of Core brands is much better than AMD's attempt at marketing with Vision.
From an architectural standpoint, the mobile Core i7-2920XM and -2820QM are closely related to the desktop Core i7-2600K. With a smaller last-level cache and slower maximum graphic clock, the Core i7-2720QM and -2630QM fall somewhere between the Core i7-2600K and i5-2500K. Just keep in mind that the -2500K doesn't have the benefit of Hyper-Threading, so it's limited to 4C/4T. Meanwhile, all of Intel's new mobile CPUs feature Hyper-Threading support.
|Core / Threads||4 / 8||4 / 8||4 / 8||4 / 8|
|Base Clock||2.5 GHz||2.3 GHz||2.2 GHz||2.0 GHz|
|Max. Turbo Clock||3.5 GHz||3.4 GHz||3.3 GHz||2.9 GHz|
|Max. Graphics Clock||1300 MHz||1300 MHz||1300 MHz||1100 MHz|
|Quick Sync Support||Yes||Yes||Yes||Yes|
As with the desktop models introduced earlier this month, Intel's mobile lineup also uses the digit '2' in front of each model to indicate membership in its second-generation Core CPU club. The 2 makes sense to us. But the three numbers that follow are arbitrary performance indicators—exactly what you grew accustomed to from the Nehalem-era CPUs. Intel uses clock rate, L3 cache, Hyper-Threading, and Turbo Boost to differentiate one model from another. It’s a safe guess, though, that -2920QM is faster than -2820QM, and so on.
You'll notice that Intel maintains the TDP profile of its previous mobile offerings. For its SV (standard voltage) Core i7s, the company keeps the limit at 55 W, which we saw with the Core i7-920XM.
The 2.3 GHz Core i7-2820XM enjoys up to eleven bins of Turbo Boost acceleration, running at a maximum frequency of 3.4 GHz in single-threaded applications. With two cores active, it drops to 3.3 GHz. And with all four working, the CPU drops to 3.1 GHz. Comparatively, the desktop Core i5-2500K starts out with a base clock at 3.3 GHz and employs four bins of Turbo Boost to get to 3.7 GHz.
The 2.5 GHz Core i7-2920QM runs as fast as 3.5 GHz in single-threaded apps, and the 2.2 GHz Core i7-2720QM clocks up to 3.3 GHz. While all mobile Core i7s include Hyper-Threading, only the top two SKUs feature an 8 MB L3 cache. The other two mobile Core i7s in Intel's 55/45 W stable are limited to 6 MB.