Intel Core i7 for laptops: first review

18 Sep 2009
Core i7 mobile close-up

Core i7 mobile close-up

When it arrived on the desktop scene, Intel's Core i7 levelled the opposition. With enough power to embarrass Intel's own Core 2 architecture, not to mention AMD's efforts, and coming at a cost that would make even a banker weep, Core i7 set the benchmark and set it high. Now, with the new Clarksfield range of processors it's set to repeat the trick in the laptop market, and we've got our hands on a sample boasting the mid-range quad-core 1.73GHz i7-820QM.

The first processors to arrive will be quad-cores based on a 45nm process, with 32nm dual-core models following in early 2010. Intel has kept the quad-core line-up refreshingly simple too, with the 1.73GHz i7-820QM flanked on both sides by the 1.6GHz i7-720QM and the top of the range 2GHz i7-920XM. Unlike their Core 2 Quad predecessors, all four cores boast Hyper-Threading; a move that allows the processors to handle as many as eight separate threads at once.

A perfunctory look at the modest-looking clockspeeds is enough to leave the keen bystander a mite underwhelmed, but those figures don't take any account of the ace resting up Core i7s sleeve - Turbo Boost.

Basically, if two or more cores are sitting unused, and the processor isn't running too hot or drawing too much current, Turbo mode kicks in and ups the speed of the remaining cores. For the i7-820QM, this can take the stock speed of 1.73GHz up to a maximum of 3.06GHz, while the i7-720QM and i7-920XM push up to 2.8GHz and 3.2GHz respectively.

Core i7 CPU-Z

Performance

If you're not bothered about the details and just want to know how fast it is, the answer is very, very fast. Take, for example, the fastest laptop we've ever seen: the Dell Precision M6400 Covet costs the same as a nice second-hand car (£4,100) and offers a Core 2 Quad QX9300 running at 2.53GHz, 8GB of DDR3 memory, a 7,200rpm hard disk and high-end Nvidia Quadro FX 3700M graphics.

That combination earned an overall score of 1.64 in our application-based benchmarks, so it was with some surprise that we saw our early i7 sample sidle up alongside with 1.59. It might not beat the Dell, but put it in perspective - the CPU is rated at just 1.73GHz, it has half the amount of RAM and a 32-bit OS installed (to the Covet's 64-bit OS), an inexpensive 5,400rpm hard disk and a far more modest GT 240M Nvidia graphics chip. Whichever way you cut it, that's an impressive achievement by the Core i7.

It's the Turbo Boost feature that really impresses, though. In our testing it worked without a hitch, dynamically overclocking cores to suit single and multi-threaded applications, while disabling unused cores to keep power consumption within acceptable limits.

Attaching a power meter to the laptop shows the Turbo Boost function in action - stress one core to 100% load and the clockspeed rises to 3.06GHz while power consumption hovers around 58W. Fully load another core and the overclock reduces to 2.8GHz and the power consumption to 70W. Load either of the two remaining cores, and Turbo Boost keeps power consumption hovering around the 70W mark by lowering the overclock to a maximum of 2GHz. Finally, with all four cores flat out, it falls to a maximum of 1.73GHz with power consumption hitting peaks of 74W.

(Click on graphs to enlarge)

Core i7 for laptops - power consumption
2GHz Intel Core 2 Quad Q9000 - power consumption
2GHz Intel Core 2 Duo T6600 - power consumption

And, if you're expecting all this power to turn your notebook into a mobile fireball, you'll be pleasantly surprised. Our test sample was a modestly-proportioned 16in laptop, and with just a single vent at its side the i7-820QM idled at about 37 degrees centigrade, only hitting 77 degrees once the CPU was working flat out. Compare that to the 2GHz Core 2 Quad Q9000 in the recently reviewed Asus G71GX gaming beast, which idles at 50 degrees and peaks at 75 degrees, and the Core i7's efficiency shines through.

As you might imagine, this efficiency helps improve battery life drastically. We rarely see quad-core laptops last more than a couple of hours even while sitting idle, but this one defied our expectations by lasting for over three and half hours with a bog-standard 4,800mAh battery. Push it to its limits, however, and our heavy usage test drained the battery in a mere 46 minutes.

Don't forget, though, if you have to work on battery you can always engage Vista's Power Saver mode - a measure which disables Turbo Boost and drops the CPU down to just 1.2GHz. In this scenario, with all four cores at full load, power consumption drops from 72W to a much more battery-friendly 52W - if you need all the benefits of multi-core computing, but longevity is important, too, then it's a measure that can raise heavy usage battery life to a far lengthier 1 hour and 15 minutes.

Conclusion

Think it through briefly, and Core i7's move to the mobile market might not make too much sense - indeed, combine huge power draw with massive heat output and you've pretty much nailed the absolute worst combination for the slimline confines of a laptop chassis.

However, Core i7 is a better match than anyone might have imagined. Several of its key features even seem to make more sense in a laptop than they do in a desktop PC, with Turbo Boost in particular making the perfect mobile match.

Price may yet prove to be a stumbling block, especially for the quad-core models, but going by the reasonable cost of Intel's desktop-based Lynnfield platform upon which the mobile i7 platform is based, we can keep our fingers crossed that the forthcoming dual-core CPUs will bring all the i7's benefits - Turbo Boost and Hyper-Threading included - to laptops of all prices, shapes and sizes.

Core i7 for laptops - 2D benchmarks
Core i7 for laptops - battery life tests

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