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Intel's '7W' Ivy Bridge chips are partly a marketing sleight-of-hand

Column But it might be okay, and might even work
Fri Jan 11 2013, 16:44

CHIP INDUSTRY WATCHERS were somewhat stunned earlier this week when Intel revealed at its CES press conference on Monday that it has begun fabbing Ivy Bridge processors that draw only 7W of power and is shipping them to device makers for use in smartphones and tablets.

However, further investigation has found that Intel's claim to have developed 7W Ivy Bridge chips at least partly rests on some marketing sleight-of-hand, and it remains to be seen how well these processors will actually perform, that is, whether Intel will get away with this clever marketing ploy in the highly competitive mobile device markets.

Technology website Ars Technica looked into Intel's 7W chip announcement and discovered that its Y series CPUs are significantly downclocked versions of its Core i3 and Core i5 processors that have been favoured with a supplementary power rating that Intel calls "Scenario Design Power", or SDP, in addition to its traditional Thermal Design Power, or TDP rating.

There's one Pentium 2129Y chip that's clocked at 1.1GHz, with a TDP rating of 10W and an SDP rating of 7W, and there's also a Core i3 3229Y chip clocked at 1.4GHz with a TDP of 13W and also an SDP of 7W. Neither of these processors has Turbo Mode and only the Core i3 processor has support for Hyperthreading. These are likely destined to be sold as low-end budget processors, but it's interesting that while they have TDP ratings that differ by 3W, they both have the same SDP rating of 7W.

Ars Technica compared two "roughly analogous" Core i5 processors and found that the Core i5 3339Y chip is clocked at 1.5GHz and 2GHz in Turbo Mode with a TDP of 13W and an SDP of again 7W, while the Core i5 3317U chip is clocked at 1.7GHz and 2.6GHz in Turbo Mode with a TDP of 17W.

Note that the Y series chip with 7W SDP is downclocked by 200MHz base frequency and by 600MHz in Turbo Mode, which explains why its TDP is 4W lower than the TDP of the similar U series chip. That's almost 12 percent slower base frequency and 23 percent slower in Turbo Boost.

All of the Y series CPUs have integrated Intel HD 4000 graphics cores like their faster U series siblings, but those are limited to 850MHz maximum speed, whereas the U series graphics cores can run at up to 1,050MHz. That's 19 percent lower maximum graphics processing speed in the Y series chips compared to the U series chips.

Thus, we can expect tablet PCs that feature Intel's '7W' Ivy Bridge processors to be at least 12 percent to 23 percent slower than similar laptops, and to be up to 19 percent slower displaying complex graphics.

Whether these performance differences will show up in commonly used benchmark tests is something that will be discovered as these chips are used in smartphones and, most likely, tablets, and benchmark tests are conducted. I'm willing to bet that these differences will be noticable, but it is possible that device usage patterns are such that they will not be noticable by users in their web surfing, emailing, tweeting and so on, and I suspect that is exactly what Intel's marketing department is counting on.

I'd expect that Intel did some testing of typical smartphone and tablet usage patterns and demands on CPU and graphics processing resources, and discovered that, at most, users of those devices stress the processor and graphics core at about 50 percent utilisation. Thus perhaps, it set its new Scenario Design Power level at 7W/13W, or just shy of 54 percent.

Decades ago, it was found that computer users were not so bothered by mediocre response times as they were by response times that varied widely. Then, users of mainframe based computer systems, such as bank tellers for example, wouldn't complain if response time was typically two seconds versus one second, but they would protest if an average two second response time was punctuated by occasional four second or longer response times.

With its Scenario Design Power rating marketing ploy, Intel might be relying on a similar set of psychological expectations to develop among mobile device users, and that they will be happy if their shiny smartphones and tablets are consistent, as opposed to really fast.

Since most PC processors are vastly underutilised almost all the time, Intel might just be right. It won't surprise me in the least. µ


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