Intel Core i7-3960X Review: Sandy Bridge-E And X79 Express

Intel's Sandy Bridge design impressed us nearly a year ago, but it was intended for mainstream customers. The company took its time readying the enthusiast version, Sandy Bridge-E. Now, the LGA 2011-based platform and its accompanying CPUs are ready.

According to Mick Jagger, it’s lonely at the top. Intel might agree. After all, for the past five years, the company has put an increasingly large gap between its fastest desktop processors and AMD’s own best efforts. Enthusiasts tend to lament the fact that a lack of intense competition means they pay more for high-end hardware. But, if you’ve been around long enough, you know that Intel’s Extreme Edition CPUs were always £800 affairs and, once upon a time, AMD’s vaunted FX-series chips used to be worth their £500+ asking prices.

The fact that the £800 price point persists today, eight years later, means Intel recognizes the extremely limited market for these flagship desktop processors and isn’t about to push one of its crown jewels even further out of reach. 

It comes as little surprise, then, to see yet another Extreme Edition processor hovering around this high price point. But this behemoth is very different than what came before.

The prior generation of flagship parts based on Gulftown came armed with six physical cores and up to 12 MB of shared L3 cache. They boasted LGA 1366 compatibility, extending the useful lives of pricey X58 Express motherboards, helping soften the blow of £400+ processor upgrades. No such luck this time; you’re facing a pricier investment.

Sandy Bridge-E, Gulftown’s successor, employs an LGA 2011 interface, requiring new motherboards based on Intel’s X79 Express Platform Controller Hub. It also comes armed with an integrated quad-channel memory controller, necessitating four-module memory kits. Oh, and then there’s the fact that Intel isn’t planning to bundle its new chips with coolers, requiring a separate purchase there, too.

Meet Sandy Bridge-E

Intel is announcing three Sandy Bridge-E-based models today, but only two will be available through the end of 2011: Core i7-3960X and Core i7-3930K. The third, Core i7-3820, is slated for a Q1 2012 introduction.

All three employ the same die, which is composed of 2.27 billion transistors and measures 434 square millimetres (making it a very big chip). In comparison, quad-core Sandy Bridge parts are made up of 995 million transistors and measure 216 square millimetres, while six-core Gulftown CPUs incorporate more than 1.1 billion transistors in a 248 square millimetre die.

Of course, Sandy Bridge-E was never intended to be a desktop processor exclusively. Rather, it’s going to emerge in the first part of next year as Xeon E5 for single- and dual-socket servers/workstations. In that context, the CPU’s size and complexity makes more sense. After all, Westmere-EX (at the heart of Intel’s more enterprise-oriented Xeon E7 family) is a 2.6 billion-transistor die occupying 513 square millimetres of space.

When Sandy Bridge-E surfaces as Xeon, it’ll offer up to eight processing cores and 20 MB of shared L3 cache. As a desktop CPU, however, it’s limited to as many as six cores and up to 15 MB of shared L3. Intel achieves this by disabling two cores and four of the die’s 16 slices of shared L3 cache.

Of course, that configuration only applies to Core i7-3960X. Core i7-3930K, which also features six cores, dips down to 12 MB of cache, revealing Intel’s ability to very granularly disable pieces of the shared L3 to suit its needs. The upcoming Core i7-3820 will employ four cores and 10 MB of shared L3 cache—essentially half of a Sandy Bridge-E die. Each core includes 32 KB of L1 instruction and L1 data cache, plus a dedicated 256 KB L2 cache. 

The clocks on all three SKUs range up and down as well. The -3960X starts at 3.3 GHz and, through the same second-gen Turbo Boost technology introduced with Sandy Bridge, speeds up to 3.9 GHz. The -3930K starts at 3.2 GHz and hits a peak of 3.8 GHz in lightly-threaded workloads. Finally, the -3820 will start at 3.6 GHz and reach frequencies of up to 3.9 GHz with Turbo Boost.

Of course, the X- and K-series chips are also multiplier-unlocked, making those stock clocks pretty much meaningless for most enthusiasts planning to tweak their systems. Intel calls the -3820 “partially unlocked.” In all actuality, it gets six 100 MHz bins above its maximum Turbo Boost setting of 3.9 GHz, translating to a ceiling of 45x.

Intel is using the same cores found in its Sandy Bridge-based CPUs. Turning off Turbo Boost, setting similar base clocks, and running a couple of single-threaded apps demonstrates the efficient execution Sandy Bridge brings to the table compared to Thuban or Zambezi.

Switching Turbo Boost back on and running Core i7-3960X in parallelized and single-threaded titles gives us a better impression of what that technology does for performance.

In an application like iTunes, which is only able to utilize one core, Turbo Boost improves performance by 12.8%. In 7-Zip (well-optimized to use available cores), it increases performance by 10.8%. The second number is surprisingly high because Turbo pushes an additional three 100 MHz bins when five or six cores are active and none of the technology’s triggers are tripped. As a result, it's tackling our compression workload at 3.6 GHz instead of 3.3.