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Power saving through marketing: Intel’s “7 watt” Ivy Bridge CPUs

The new CPUs definitely save some power, but not as much as you might think.

Power saving through marketing: Intel's “7 watt” Ivy Bridge CPUs
Andrew Cunningham

Intel spent most of its press conference yesterday talking about future products, but there was one announcement with a more immediate impact: new 7 watt Ivy Bridge processors are shipping to Intel's partners now for inclusion in products this spring and summer.

These new CPUs appear to represent quite a substantial power savings over the processors shipping in most Ultrabooks today, which have a 17 watt TDP, but Intel's marketing slides don't quite tell the whole story. We talked with Intel representatives, went hands-on with Lenovo's IdeaPad Yoga 11S, and did some sleuthing on Intel's CPU product pages to see what kind of power consumption and performance we can actually expect from these processors.

“Scenario Design Power”

The particular Ivy Bridge processor in the IdeaPad 11S we got our hands on was a Core-i5 3339Y, a 1.5GHz dual-core processor with Hyperthreading and Turbo Mode support up to 2.0GHz. There are both cheaper and more expensive CPUs in the lineup, but this one probably represents the best combination of features and price—we expect it will be one of the more popular selections for Ultrabooks and tablets based on these processors, much like the Core i5-3317U is now.

Detailed information on this processor is up on Intel's ARK site for anyone who bothers to look it up, and it immediately reveals a bit of fancy footwork on Intel's part: the actual thermal design power (TDP) of that processor is listed at 13 watts. The 7 watt number advertised during Intel's keynote yesterday is actually from a new metric, "scenario design power" (SDP), which purports to measure how much power the CPU is using during average use.

SDP is a new unit of measurement for Intel, and the company doesn't list an SDP number for its current 17 watt low-voltage processors. These new processors do save power compared to previous models, but in an apples-to-apples comparison it only ends up to be about 4 watts, not the 10 watt savings it appears to be in Intel's marketing slides.

Intel's "7 watt" Y-series CPUs
CPU CPU Clock/Turbo speed CPU cores/threads GPU GPU base/max speed Max TDP SDP
Pentium 2129Y 1.1GHz 2/2 Intel HD Graphics 350/850MHz 10W 7W
Core i3-3229Y 1.4GHz 2/4 Intel HD Graphics 4000 350/850MHz 13W 7W
Core i5-3339Y 1.5GHz/2GHz 2/4 Intel HD Graphics 4000 350/850MHz 13W 7W
Core i5-3439Y 1.5Ghz/2.3GHz 2/4 Intel HD Graphics 4000 350/850MHz 13W 7W
Core i7-3689Y 1.5GHz/2.6GHz 2/4 Intel HD Graphics 4000 350/850MHz 13W 7W

Note that there is one processor which manages a 10 watt TDP, the low-end Pentium 2129Y. That processor's lowly 1.1GHz clock speed, weaker GPU, and lack of features like Hyperthreading and Turbo Mode mean that it's probably destined mostly for budget systems, however.

Performance

Neither Intel nor Lenovo would let us run any of our benchmarks on their pre-release IdeaPad 11S units, but the ARK product pages tell us most of what we need to know about the processors' performance. Let's compare the i5-3339Y to the popular (and roughly analogous) 17 watt processor, the i5-3317U.

CPU face-off: 17 Watt vs. 13 Watt
CPU CPU Clock/Turbo speed CPU cores/threads GPU GPU base/max speed Max TDP SDP
Core i5-3339Y 1.5GHz/2GHz 2/4 Intel HD Graphics 4000 350/850MHz 13W 7W
Core i5-3317U 1.7GHz/2.6GHz 2/4 Intel HD Graphics 4000 350/1050MHz 17W N/A

These CPUs feature the same basic features, graphics processors, and manufacturing processes, so if you're going to save power there's really only one thing to cut: clock speed. The Y-series processor only loses a little in base clock speed—1.5GHz compared to 1.7GHz—but you lose 600MHz in Turbo Boost speed, which could result in as much as a 23 percent reduction in single-threaded performance, assuming that performance scales linearly with clock speed.

These chips will still be plenty fast for the kinds of tasks that Ultrabooks based on U-series CPUs usually perform—word processing, Web browsing, and on-the-go photo and video processing. Whether you notice the speed hit in real-world usage will depend on the kinds of tasks you usually do.

You also lose some graphics speed, though thankfully you retain all of the core features of Intel's HD 4000-series GPU, including QuickSync, Wireless Display, and support for APIs like DirectX 11, OpenGL 4.0, and OpenCL 1.1. The base graphics frequency of 350MHz is the same, but the Y-series chip tops out at 850MHz, down from 1.05GHz in the U-series chip. Again assuming performance that scales fairly linearly with clock speed, you'll lose about 19 percent of your performance compared to the analogous U-series CPU (and slightly more in CPU-bound games that are also adversely affected by the drop in CPU clock speed).

We'll continue trying to get our hands on a system for some actual benchmarking, and we'll update this article if we're granted access to one of the pre-production systems.

Conclusions

In the end, Intel has saved power in its new Y-series CPUs in the least surprising way possible—not through improvements to the 22nm manufacturing process or aggressive processor binning, but through clock speed reductions and some fancy marketing footwork.

The new CPUs are more power efficient, but not massively so. It's also worth noting that the CPU is but one piece of the puzzle in your PC—the RAM, disk, monitor, and other components also need to be accounted for—this, plus the actual 13 watt TDP of these new Ivy Bridge processors, helps to explain why PCs like Microsoft's Surface Pro (which is rumored to be using these newer Y-series CPUs) still have mediocre battery life.

What this all means is that, though these Y-series CPUs will enable slightly thinner and more power efficient designs in the short term, we're still going to be waiting for Haswell to see big reductions in power usage. Though our Intel rep told us that the TDP and SDP numbers for low-voltage Haswell processors are expected to be about the same as these Ivy Bridge models (unsurprising, given that they're both produced on the same 22nm manufacturing process), remember that Haswell is also bringing a few more power-saving technologies to bear. The most notable of these are the new "active idle" power states that allow systems to go to sleep more quickly, more often, and more transparently than today's PCs.

Update: In an earlier version of this article, we gave an Intel's representative's estimate of an SDP number for the U-series Ivy Bridge processors. We have been told that that number is not accurate, and that Intel doesn't have SDP figures for these processors.

Channel Ars Technica