Intel Sandy Bridge Extreme

The need for speed

It's now three years since Intel released the Core i7 processor and associated X58 chipset, making up the LGA1366 platform. Then ushering in a new era for high-performance PCs and with numbers still to be bettered by AMD's rival Bulldozer chip, Intel's has the high-end desktop market sewn up for a while.

Enthusiasts flocked to the now-defunct Core i7 920 - a quad-core, eight-threaded chip available, at the time, for sub-£200 - and Intel extended the LGA1366 platform's usefulness by wielding an improved range of chips hewn from a 32nm process that sport six cores and 12 threads, though stratospheric pricing keeps them out of the reach of most.

Scribble down a PC wishlist and Intel's Core i7 990X is the bee's knees. Saliently putting the £770 asking price aside for a moment, the 3.46GHz chip is the fastest consumer CPU available - no ifs, buts or maybes, and Intel can readily release a '995X' that's nothing more than a minor clock bump - the architecture still has frequency legs to spare.

But the chip giant is committed to investing in new architectures and releasing chips on what it terms a tick-tock strategy. Unfortunately for Core i7 (LGA1366) and X58, powerful as they doubtless are, they're considered yesterday's news. Today's hottie is the excellent mainstream Sandy Bridge range, better known to you as the second-generation desktop Core i3/i5/i7. These chips excel in many areas, not least with respect to the diametrically-opposed attributes of low power consumption and tip-top performance.

Intel, then, has taken all this Sandy Bridge know-how and brought it to bear on a trio of high-end processors that are the natural successor to LGA1366/X58. Say hello to the Sandy Bridge Extreme.

First off, here's a very high-level overview of how the new chips compare with existing premium Intel models. This'll provide a solid footing for analysing architecture changes during this discourse.

More of the same?

There are to be three new chips based on the Sandy Bridge Extreme architecture: the Core i7 3960X, 3930K and 3820. The trio share a number of similarities with the incumbent LGA1366 high-end chips, as both sets of CPUs are based on Intel's established 32nm technology, run without any form of pre-plumbed integrated graphics, have a 130W TDP, and, tellingly, share the six-core, 12-thread setup (Core i7 3820 excepted).

If it's more of the same but with a tweak here or there, what gives, because it's been a while since the Core i7 980X/990X's inception, right? Well, let's do the sensible thing and compare top-line part vs. previous top-line part.

Core i7 3960X vs. Core i7 990X

A spare $999 will buy you either a new-generation Core i7 3960X or last-gen Core i7 990X. The newer chip's actually clocked in a little lower, at 3.3GHz - matching Core i7 980X EE - but that figure isn't important. What's more interesting is the Turbo Boost frequency which is the speed the chip's cores can run at under certain constraints. One benefit of the Sandy Bridge architecture presents itself here, as the Core i7 3960X uses v2.0 of Turbo Boost. What this really means is the processor can boost speed better than the 990X in all circumstances, and here's how:

You see, the native speed is practically irrelevant if Turbo Boost is switched on in the BIOS, and there is no reason why it shouldn't be.

The Core i7 3960X matches the Core i7 990X's speed when five or six cores are used and beats it if fewer cores are active. Not escaping the eye of the eagled-eyed SCAN reader, Core i7 3960X continues with Sandy Bridge's 100MHz base clock, meaning multiplier jumps are 100MHz, not 133MHz, per the older Core i7 990X. The takeaway here is that Intel is making better use of the chip's TDP, maximising performance through a more-granular Turbo Boost implementation.

More bandwidth

The next meaningful boost comes way of more available memory bandwidth. Core i7 3960X uses an extra memory channel - one DIMM per channel - that's also officially rated at a higher speed than Core i7 990X's three-channel, DDR3-1,066, though this is pragmatically misleading as practically every X58 board allows one to increase memory speed to 1,600MHz. But comparing like for like, Core i7 3960X can tap into 51.2GB/s compared to Core i7 990X's 25.6GB/s - or exactly double. Be aware that the cache design and consumer desktop applications' usage has historically meant that a super-abundance of memory bandwidth isn't necessarily realised.

Different socket - more cost?

This one's rather obvious in the move between architectures. Intel's decision to include a fourth memory channel and a plethora of behind-the-scenes tweaks is manifested by a chip that's well, just plain larger. Core i7 3960X uses an LGA2011 socket and, therefore, requires a new supporting chipset called X79.

Counting the cache

Here's 3960X in another high-level overview. Per-core L1 and L2 cache remains the same. However, L3 is boosted from 12MB to 15MB, and in many ways this counteracts the benefits of quad-channel memory-controller. Whatever the design implications, more cache is almost certainly always better. Though Intel hasn't spilled any further details on the matter, it would be reasonable to assume that 32nm Sandy Bridge has a myriad of cache tweaks aimed at streamlining throughput.

ISAs and interface

Rolling in with Sandy Bridge is AVX extensions, making these new chips more efficient at processing floating-point-intensive instructions used in applications such as image- and video-editing software, which rely heavily on SIMD optimisations. But we'd challenge you to find more than a handful of AVX-optimised apps for the consumer market, making this more of a specification tick than real-world benefit right now.

And further underscoring the Sandy Bridge heritage is Intel's decision to run with DMI 2.0 as the chip-to-system interconnect, supplanting the QPI found on Core i7 990X. DMI 2.0 has a peak transfer rate of 20Gb/s through a x4 link.

3960X summary

A brief examination of the new Core i7 3960X's architecture suggests it should be a little faster than 990X when evaluated over a wide range of benchmarks. The main instigators of this performance increase are: greater memory bandwidth, AVX extensions, better Turbo Boost implementation and general behind-the-scenes tweaks that inevitably occur when moving from one microarchitecture to another.

The Core i7 3960X pulls a 5-15 per cent lead over 990X in a straight CPU-to-CPU fight - more so if the application is tailored for Sandy Bridge's improved ISA. One has to remember that the new chip isn't all that different to the Westmere/Gulftown 990X in the vast majority of ways, and it will take Intel transitioning to an eight-core, 16-thread design before genuinely big-dollop performance improvements are seen.

Who has a thousand bucks?

Intel, though, is introducing more than one Sandy Bridge Extreme chip at this juncture. The better bet, financially speaking, is the $564 (£450) Core i7 3930K. Look back at the first table and it's apparent that this second-rung chip is no poor cousin. Running at almost the same frequency and unlocked so that you can push it as high as you like, it'll just lose a touch of performance by having 20 per cent less L3 cache - 12MB vs. 15MB.

Core i7 3930K makes far more implicit sense than Core i7 3960X, too, because it's logical to assume that initial runs of both chips are harvested from the same wafers, intimating comparable overclocking potential. Why not get a Core i7 3930K and jack it all the way up to, say, 4,700MHz (47 x 100MHz BCLK) and beat the pants off a stock-clocked Core i7 3960X? Scan's customers are likely to do just this.

But perhaps the most interesting of the trio is the four-core, eight-threaded Core i7 3820. Its pricing is below the just-launched Core i7 2700K, but limited overclocking control - usually the benefit of having a K-series chip - lack of integrated video outputs and expensive motherboard support count against it.

Anyway, three new performance chips cement Intel's position as the provider of the fastest consumer CPUs for high-performance desktop systems. Scan has a full range of chips that can be seen here.