Intel Dual-Core Mobile Ivy Bridge Launch and i5-3427U Ultrabook Review

Captain's Log, Stardate 20531.0: Dual-Core Ivy Bridge Spotted

After April’s launch of quad-core desktop and mobile Ivy Bridge parts, today Intel is launching the smaller, cheaper, and lower powered dual-core half of the IVB family...but only for mobile users. The i7 and i5 parts will be launching today, while budget-seekers looking for i3 parts will need to wait until Q3 to get their IVB fix. If you're looking for additional information on the desktop parts, we don't have much to discuss right now as those are also slated for Q3'12, but Anand does have a writeup of the i5-3470 with HD 2500 Graphics. As we've noted in the past, Intel continues to focus more and more on their mobile products, and dual-core Ivy Bridge continues that trend. Since Intel is really pushing their Ultrabooks for mobile users, we'll start there.

At the low end of the power scale and primed for use in Ultrabooks we have the Ultra Low Voltage (ULV) IVB family, which is composed of four chips—a pair of i7s and a pair of i5s, with one OEM model in each family. As is customary for the Core i-Series ULV parts, all of these chips have a 17W TDP and run at fairly conservative base clock speeds in order to keep their TDP in check. For the most part Intel is playing it straight here, with the primary differences between the chips being CPU and GPU clock speeds, L3 cache sizes, and of course price.

At the top of the lineup is the i7-3667U, which ships at a base clock speed of 2GHz and can turbo up by at least 50% to 3.0GHz with two cores active or 3.2GHz with one core active. Compared to its SNB predecessor this is 200MHz higher on the base clock and 400MHz/300MHz higher on the turbo clocks in the same 17W envelope, so in CPU-bound scenarios the i7-3667U should pack a noticeably bigger punch. That's in addition to minor performance enhancements with the Ivy Bridge microarchitecture, which should account for another ~5% performance increase at the same clock speed on average.

Of course with Ivy Bridge the biggest performance increases are on the GPU side. All of the ULV IVB CPUs ship with Intel’s HD 4000 iGPU, which brings with it a 33% increase in the number of EUs on top of support for DX11 and OpenCL. Compared to SNB the graphics clocks are largely unchanged—350MHz is still the GPU base clock speed while the turbo clock speed has been dropped from 1200MHz to 1150MHz—so the bulk of the performance improvements will be from the larger number of EUs, IVB’s ability to turbo more often, and of course the architectural improvements Intel has made for this generation.

Intel's prototype Ivy Bridge Ultrabook

Fleshing out the rest of the ULV lineup, we have the i7-3517U that runs at slightly lower clock speeds, and then the i5-3427U and i5-3317U. Along with still lower clock speeds, the i5 ULV CPUs also give up 1MB of L3 cache, leaving them with 3MB of L3. All of the ULV CPUs feature VT-x and AES-NI support, so Intel is leaving the most critical features available on the entire lineup, however business buyers will want to take note that the OEM-only parts—i7-3517U and i5-3317U—do not feature Intel’s Trusted Execution Technology (TXT) or vPro.

The other family of dual-core mobile IVB CPUs being launched today is the Standard Voltage (SV) lineup, which is composed of CPUs that operate at 35W. With the bulk of Intel’s i7 mobile IVB lineup focused on quad-core CPUs, there’s a single i7 here along with three i5s. The i7-3520M has a base clock speed of 2.9GHz and can turbo up to 3.4GHz and 3.6GHz with two and one active cores, respectively. Meanwhile the GPU base clock is 650Mhz and can turbo up to 1250MHz. Compared to the outgoing SNB based i7-2640M, this is only a 100MHz bump, so the CPU performance difference isn’t going to be quite as remarkable as on the ULV lineup, though we still expect these IVB CPUs to be able to turbo higher and more often.

Meanwhile the i5 versions of these CPUs take the requisite clock speed and L3 cache reductions. All three i5 CPUs have 3MB of L3 cache, base clock speeds between 2.5GHz and 2.8GHz, and of course lower prices. The HD 4000 GPU’s base clock speed is 650MHz for the entire lineup, while the maximum turbo clock is between 1100MHz and 1200MHz. The entire SV mobile IVB lineup features AES-NI and VT-x, and with the exception of the OEM-only i5-3210M, all of them feature TXT and vPro as well.

Finally, the chipsets these CPUs will be paired with should be familiar to you; Intel is using the same 7-series mobile chipsets that they first launched last month with quad-core mobile IVB, though we do have a bit more information on them compared to last month, particularly regarding power consumption.

With the increasing number of functions handled by the CPU there are fewer and fewer things left for the supporting chipset, which makes many of the chipsets quite similar. Mostly, it's a question of maximum USB ports, PCIe lanes, SATA ports, and power envelope. UM77 is going to be the best candidate for use in Ultrabooks as it has the lowest TDP and lowest average power consumption thanks to its lack of VGA and LVDS monitor support. At the same time with only 4 PCIe lanes available from the chipset, it's only going to have enough bandwidth for Thunderbolt and little else (and at least one of those lanes will be used by a mini-PCIe slot for WiFi). Otherwise QM77, HM77, and HM76 all share the same 4.1W TDP and 1.22W average power and are more likely to be found alongside 35W CPUs.

With the CPU and chipset overview out of the way, it's time to get to the meat of today's review: the Ivy Bridge Ultrabook. Wait, what about architecture changes, die sizes, transistor counts, and all of those good tidbits? We've covered the architecture side already, and the only real change is in the loss of two cores and some of the L3 cache. Sadly, Intel didn't provide any information on how that affected die size or transistor count.

What we do know is that the quad-core Ivy Bridge die is 160mm² and has 1.4B transistors. We did some quick and dirty estimates based on the removal of half the L3 cache and two CPU cores, and it looks like a dual-core IVB die should be in the neighborhood of 120mm², but that's just an estimate. There are also rumors circulating that Intel might be harvesting quad-core die for dual-core use as well; that's certainly possible, though it seems unlikely the ULV parts would be harvested chips. Unfortunately, we don't have much else to say on the CPU die beyond that. We'll update with any additional details if we receive them, but now let's see what Intel has planned with their Ultrabook update.

Update: We cracked open the Zenbook Prime UX21A and measured its Core i7-3517U dual-core/GT2 Ivy Bridge CPU.