The U is for Ultrabook: Intel’s low-power, dual-core Haswell CPUs unveiled As it turns out, the CPU may be the least interesting thing about Haswell.

The U is actually for "Ultra-low voltage," but either way we're looking at laptop CPUs.

On Saturday, Intel officially took the wraps off its first next-generation desktop and laptop CPUs based on the "Haswell" architecture. Absent from that reveal, however, was any mention of the low-power laptop CPUs that will carry Intel's Ultrabook initiative into 2014. Turns out Intel was just saving those particular announcements for Computex proper. Now, we can finally talk about the dual-core parts in the Haswell rollout.

A single low-power Core i5 chip is the only desktop part being announced today. The other 16 CPUs that are being unveiled are all U, Y, and M-series chips aimed straight at the mainstream, thin-and-light laptops and tablets (as well as the convertible PCs that Windows 8 has made so common).

We gave a high-level recap of Haswell's features in the original announcement piece, and we won't go back over that ground here: the basic CPU architecture, the changes to the GPUs, and the new 8-series chipsets are the same whether we're talking about dual-core or quad-core Haswell chips. What we'll cover now are changes to the U- and Y-series' power consumption, the kinds of machines that Haswell can fit into that Ivy Bridge had trouble with, and the specific CPUs that are being announced today.

As we said in our last write-up, keep in mind that all of the numbers below come directly from Intel, who will be working hard to present their processors in the best possible light. We'll be examining these performance and power consumption claims more fully when we have production Haswell systems to test with.

Evolving the Ultrabook

With Haswell, Intel is expanding the list of requirements needed for OEMs to be able to use the "Ultra book" moniker. Note that Intel Wireless Display and touchscreens are now required, and that Intel "recommends" convertible designs in the fine print at the bottom of the slide.

Intel's Ultrabook strategy with Haswell is roughly the same as it was with Ivy Bridge: the majority of the low-power processors will be part of the ultra-low-voltage U-series intended for most laptops and laptop-like convertibles (think the Dell XPS 12 or the Lenovo IdeaPad Yoga). These CPUs will have 15 watt TDPs, down from 17 watts in Sandy and Ivy Bridge.

With Haswell, Intel will also be pushing "behind the glass" convertible PCs more emphatically than they could with Ivy Bridge. If you can't guess, these are convertible laptops that store their hardware behind the screen rather than in the base of the laptop, enabling you to take all of your processing power with you if you remove the screen from the keyboard. Designs like this exist today, but many of them are based on slower ARM and Intel Atom processors. Trying to put Ivy Bridge chips "behind the glass" can result in bulky tablets like Acer's Iconia W700 and the hot-running Microsoft Surface Pro.

 U- and Y-series Haswell chips have their chipsets integrated on to the same package as the CPU itself, making the advertised TDP reductions even more significant.

The Haswell Y-series CPUs are much like the Ivy Bridge-based ones we saw at CES, complete with slightly confusing power envelopes. These CPUs have an 11.5 watt TDP, down from 13 watts in the Ivy Bridge versions. The sticking point is what Intel calls "scenario design power," or SDP. We explore just what SDP means more fully in this article, but the short version is that OEMs can configure the U- and Y-series chips to hit a lower TDP than the 15 and 11.5 watt maximums. This is something OEMs could always do if they really wanted, but beginning with the Y-series chips Intel now validates the CPUs for operation at these lower power levels.

This adjustment comes at the cost of some performance, but it can allow the chips to consume less power and fit into smaller enclosures without requiring Intel to further complicate its already overcomplicated product matrix. The Y-series CPUs have a six watt SDP, down from seven watts in Ivy Bridge, and they also have a 9.5 watt "CTDP" between the max TDP value and the SDP value. U-series CPUs also have a CTDP of 11.5 watts, but don't have a validated SDP value.

The advertised power consumption figures for the ultra-low-voltage Haswell chips are a bit more impressive once you consider that the chipset is actually integrated into the same package for these CPUs rather than being a separate chip (as in Ivy Bridge and its predecessors). For instance, the Ivy Bridge U-series chips had a 17 watt TDP, and the chipset itself had a separate TDP of three watts (adding up to a total of 20 watts). The 15 watt TDP figure for the U-series Haswell chips includes the chipset, making for a 25 percent combined reduction in TDP.

"SDP," the sort-of-nebulous power measurement introduced by Intel at CES this year, returns for Haswell.

Combined with the "active idle" power state, which allows Haswell laptops do more when idle and transition between active and idle states more quickly, Haswell has the potential to enable significantly better battery life for general-usage workloads. We'll need to see some production Haswell laptops before we can put these claims to the test, but on paper they're very promising.

Integrating the chipset into the CPU package also slightly reduces the amount of space on the PCB that the chips take up, leaving more room for batteries, RAM, or other components. Soldered-on memory has become an unfortunate fact of life for many Ultrabooks these days, but at the very least I'd like to see laptops with 4GB of it go by the wayside.

All of this adds up to a set of improvements that don't radically change the Ultrabook form factor, but they may solve some of the problems keeping certain Ivy Bridge Ultrabooks and tablets from being great. Ivy Bridge tablets like the Surface Pro are the strongest case in favor of this argument, but the poor battery life of Acer's original Aspire S7 or Asus' twin-screened Taichi are also good examples. Haswell might not enable radical form-factor changes, but we suspect that several almost-great Ivy Bridge devices will be able to use Haswell to get the boost they need.

The products

The lone dual-core desktop CPU being unveiled today.

We'll hit the lone desktop CPU in the lineup first: the Core i5-4570T has a 35 watt TDP, but it gives up two of its cores to do so. It attempts to make up for these missing cores by including Hyperthreading (the only desktop i5 to do so) and much higher clock speeds than the quad-core 35 watt i7 (2.9GHz base and 3.6GHz Turbo, compared to the i7's 2.0GHz base and 3.0GHz Turbo). It also gives up 2MB of L3 cache, dropping to 4MB where the other desktop i5s include 6MB.

More dual-core desktop CPUs will undoubtedly follow the Core i5s and i7s in the coming months—Intel tells me that Haswell Pentiums and Celerons will be here eventually, and Core i3s are a sure bet. These lower-margin parts typically trail the high-end CPUs by a few months, though, so until then the 35 watt i5s and i7s are your best bets for low-power desktop CPUs.

Mainstream, M-series laptop CPUs. In total, there are 11 announced CPUs in the M, MQ, and MX families, and two more will be announced by the end of the year. Whether these will be dual- or quad-core parts hasn't been announced.

Moving on to laptops: the "M" in these processors' names could stand for "mainstream" just as easily as "mobile." They're the meat-and-potatoes 37 watt processors that you're going to find in mainstream laptops, rather than eye-catching Ultrabooks or powerful workstations. Interestingly, this 37 watt TDP is slightly higher than the 35 watt TDP of the equivalent Ivy Bridge parts, and unlike the U- and Y- series chips the M-series parts don't have an integrated chipset on which to blame this increase. Remember, though, that TDP is more a measurement of worst-case-scenario power usage rather than actual power usage for real workloads. The improvements to Haswell's power consumption when idle means that, in general, power usage should still be lower than in Ivy Bridge.

All six of these chips have two CPU cores plus Hyperthreading, and all six use the HD Graphics 4600 part—this should give better graphics performance than Ivy Bridge's HD 4000 but not quite as much as in the HD 5000 GPU available in some of the U-series CPUs. The maximum GPU clock speeds differ slightly depending on what CPU you've got, topping out at 1.3GHz in the i7, 1.25GHz in the i5s, and 1.1GHz in the i3s. The Core i3 CPUs also give up the Turbo Boost feature available in the i5s and i7s, as well as features like vPro, TXT, and VT-d.

The U-series Ultrabook CPUs, an increasingly important category for Intel. Eight are being announced today, with ten more to follow by the end of 2013.

As in Ivy Bridge, the U-series chips are going to be the ones we see the most often in Intel's Ultrabooks. All of the parts feature a 15 watt TDP, two CPU cores with Hyperthreading enabled, and either 4MB (Core i7) or 3MB (Core i5 and i3) of L3 cache. As in the M-series, the i3 CPUs give up Turbo Boost and a couple of other features.

Where things get interesting is in the GPUs: four of these chips, two i7s and two i5s, come with Intel's amped-up Intel HD 5000 GPU, which is said to bring roughly 1.5 times the performance of the HD 4000 GPU used in the Ivy Bridge Ultrabook parts. The other CPUs—the weakest i7 and i5 and both the i3s—come with the HD 4400, which I suspect differs from the HD 4600 primarily in clock speed. The minimum GPU speed is now 200MHz, down from 400MHz in the 4600, and the maximum speed is 1.1GHz in the i7 and 1.0GHz in the i5 and the i3s.

Those more powerful HD 5000 GPUs come with a cost, however, namely in lower base CPU clock speeds for the CPUs that include them. The architectural improvements Haswell brings to the table should close that gap most of the time (as should the higher Turbo speeds, at least for short bursts of activity), but the maximum CPU performance of the Haswell-based Ultrabook CPUs with the HD 5000 may actually be level with or perhaps a bit lower than the peak performance of the analogous Ivy Bridge parts.

The even-lower-power Y series CPUs offer better performance than Atom or any ARM SoCs, but they aren't as powerful as the U- or M-series chips.

The ultra-ultra-low-voltage Y-series of processors, intended for smaller Ultrabooks and tablets, were introduced relatively late in Ivy Bridge's run. The Haswell versions of those parts will end up in the smallest and thinnest of the Haswell Ultrabook designs, especially the tablets and "behind-the-glass" convertible PCs that Intel is chasing with the chips.

There are only two chips in the Y-series that are being announced today, out of ten Y-series SKUs supposedly coming out this year: one Core i5 chip and one Core i3. Both have 11.5 watt TDPs, both have 3MB of L3 cache, and both are dual-core chips with Hyperthreading enabled. The chief difference is that the i5 supports Turbo Boost and the i3 does not. The GPUs also differ (the i5 uses an HD 4400 while the i3 has an HD 4200), but since both of the GPUs use the same clock speed as the differences between the two may be related to features rather than 3D performance. We won't know for sure until Intel gives us more information.

Will Haswell go places where Ivy Bridge can't?

Like the quad-core chips, the dual-core versions of Haswell are noteworthy for their GPUs and power usage, both of which will enable them to power different types of computers than existing Ivy Bridge chips. The Haswell chips' CPU performance will, at best, be a modest improvement over Ivy Bridge, and in the case of the U-series chips with the amped-up HD 5000 GPUs general CPU performance may hold even or regress slightly compared to similar Ivy Bridge parts.

The HD 5000 GPU is particularly interesting. In current Ultrabooks, that large a boost to graphics performance could make these thin-and-light laptops quite a bit more credible as light gaming machines or CAD workstations. It could also open the door to more laptops with high-density displays—the HD 4000 is capable of driving them, but not without occasional stuttering.

Likewise, the power consumption improvements could help some of Core-based tablets and convertibles become a bit less unwieldy than some of the Ivy Bridge ones we've seen. They'll still likely need fans to stay cool, but Haswell will allow them to reduce the size of their batteries and motherboards. This means reductions in size and weight while keeping battery life and performance roughly level.

There will probably be quite a few Haswell systems that are just slightly-improved versions of the Ivy Bridge Ultrabooks we've been seeing for the last year. Between the power savings and the reduced PCB space necessary to use these CPUs, I suspect that many a tablet or convertible that was just a bit too hot or heavy with Ivy Bridge will be able to find a better balance between size, battery life, and performance with Haswell. However, we'll actually need to see more Haswell-based systems before we can make that call for sure. We'll be watching the news out of Computex this week and rounding up the most interesting Ultrabooks for you in the coming days.