Intel Core i7 3960X £750

14th Nov 2011 | 09:01

Intel Core i7 3960X

The ultimate desktop processor could actually be even more ultimate

TechRadar rating:

4 stars

Could have been a fantastic chip. But they turned two cores off. So it isn't.


The fastest processor you can buy; Hefty overclocking headroom;


Very expensive; They turned the bloody cores off!;


A new high-end processor from Intel is normally a cue for much rejoicing. After all, who doesn't like exciting technology and the promise of epic new levels of performance? In that context, the all-new Intel Core i7-3960X is as snazzy as they come.

It's a properly new chip, not an upclocked respin of an existing design. It even comes with a new socket and chipset, known respectively as LGA 2,011 and Intel X79.

But there's another side to the story of this chip, otherwise known as Sandy Bridge E. And it's symptomatic of a broader problem with the PC platform.

The story starts with a history lesson - the origins of multi-core PC processing.

It all began when Intel realised its fascination with frequency was on the verge of failure. The chip in question was the infamous Pentium 4 processor.

In its first and second generation iterations, Pentium 4 looked pretty clever. It rapidly scaled from a little over 1GHz all the way to 3GHz.

Then the die shrink to 90nm arrived and the wheels fell off.

That was June 2004 and the first significant date on our journey from a frantic fight for frequency to what increasingly looks like multi-core malaise.

Intel's response was to cobble a pair of Pentium 4 processors together and create the Pentium D dual-core processor of 2005. The Pentium D was then superceded in summer 2006 by the much revised dual-core Core 2 family, which in turn begat the quad-core Core 2 in early 2007.

Just like Intel promised, we were on a fast track to multi-core computing.

In hindsight, that's when the problems began. It took a further three years for Intel to release the six-core Gulftown desktop processor, sold initially as the Intel Core i7-980X. And here we are today with the launch of Intel's latest and greatest, a chip that defenestrates Gulftown's Westmere architecture in favour of Intel's fancier Sandy Bridge design.

But it's still only got six cores.

What, exactly, is going on? Things become even more intriguing when you discover Intel already sells server processors with up to 10 cores.

That's right, 10 cores.

Then you look at the die shot that Intel has released for the new Core i7-3960X and realise this new six core isn't quite what is seems. In fact, it's a little bit fishy.

Time to find out more.


Intel core i7 3960x

First, let's address the elephant in the room.

There's no mention of it in Intel's official documentation, but the image Intel has provided of the new Intel Core i7-3960X's die makes one thing perfectly clear: this is an eight-core PC processor with two cores disabled.

For now, we can only speculate on Intel's strategy, even if we do have a pretty solid hunch. But more on that in a moment.

Architecturally, the Intel Core i7-3960X is part of the the Sandy Bridge family. That makes it a 32nm processor with thoroughly revised internals compared with the previous six-core Gulftown processor. That, too, is a 32nm chip, but its Westmere-vintage architecture is merely a die shrink of the earlier Nehalem family.

Not that Nehalem, Westmere and Gulftown are stinkers. Quite the contrary.

The point is that the Core i7-3960X and its sister Sandy Bridge E chips bring Intel's high-end processor offering up to date.

Predictably, therefore, many of the best bits of Sandy Bridge already seen in processors for the LGA 1,155 socket make an appearence.

That means everything from Intel's latest iteration of Smart Cache, Hyper-Threading and Turbo Boost are all in the mix. Likewise, you get support for the latest SSE4.2 instructions, along with AVX and AES extensions.

There are also a number Sandy Bridge E-specific extras that don't apply to previous Sandy Bridge chips and are largely related to the chipset and peripherals.

Socket lga 2,011

Most obvious is the new LGA 2,011 socket, which has a big increase in pins over the Intel's existing LGA 1,366 high-end desktop socket. The explanation is an upgrade from a triple to a quad-channel memory interface.

Now, Intel's LGA1,366 platform was hardly memory starved in the desktop environment. What's more, since Intel is sticking with six cores on the new i7, increased demand for bandwidth is likely to be marginal.

But here's the thing. Just like the LGA 1,366 platform, LGA 2,011 is really a server and workstation solution that Intel has given a quick buff, changed a few names on and chucked onto the desktop.

Four channels of memory is handy when you're talking about multi-socket systems with as many as 10 cores per socket. For a single-socket desktop platfrom that maxes out at six cores, it's overkill.

Anywho, other changes in the shift from LGA 1,366 on the old X58 chipset to LGA 2,011 on X79 include a single-chip chipset, PCI Express moving onto the processor die and an extra four PCI Express lanes for a grand total of 40.

Plenty, in other words, for multi-GPU action in just about any flavour you fancy.

The SATA ports also get an upgrade to 6Gbps. But there's no native USB 3.0, which is a bit of a bummer.

However, the really critical areas where the Core i7-3960X deviates from previous Sandy Bridge processors are twofold and not entirely unrelated. Again, we're talking about the uncore stuff.

Most notably, Sandy Bridge E is a pure CPU, there's no integrated graphics and that means no Quick Sync video encode acceleration. That's not an absolutely critical omission, but it is a little hard to swallow in the context of the 3960X's premium pricing.

Quick Sync is a nice feature and something you get even on the lowliest of LGA1,155 Sandy Bridge chips.

Sandy Bridge E's final change up involves overclocking.

Intel has introduced a new divider between the baseclock and the cores, known as the CPU strap. The net result of it is that baseclocks of 100MHz, 125MHz, 166MHz and 250MHz are available. Now, for an unlocked chip such as the 3960X, that's not a terribly big deal. You have full access to the standard CPU ratios on a per-core basis.

But for the more affordable partially locked members of the Sandy Bridge range, specifically the upcoming quad-core Core i7-3830, it makes all the difference and ensures the LGA2,011 platform offers something extra for enthusiasts.


Unfortunately, AMD's new Bulldozer-based FX processors aren't even in the same ballpark as the new Intel Core i7-3960X for performance. So it's Intel's own Core i7-980X that provides the competition. With similar clock speeds and the same core count, it a battle of architectures.

As our results show, the Sandy Bridge architecture is better across the board than the 980X's Westmere-vintage transistors.

Question is, is the gap big enough to justify an upgrade? When you factor in the Intel Core i7-3960X's impressive overclcoking headroom, it might just be.

CPU multi-threaded rendering performance

Intel core i7 3960x

CPU single-threaded rendering performance

Intel core i7 3960x

CPU video encoding performance

Intel core i7 3960x

Memory bandwidth

Intel core i7 3960x

CPU gaming performance

Intel core i7 3960x

Platform power consumption

Intel core i7 3960x

Intel core i7 3960x

Overclocking performance

Intel core i7 3960x


Intel core i7 3960x

Out of the box, one thing is clear. The new Intel Core i7-3960X is in a class of its own.

That, of course, isn't terribly surprising. AMD's new pseudo eight-core FX processors are well behind the old Gulftown Core i7 processors on performance. So, they were hardly likely to give this new Core i7 anything to worry about.

The contest, therefore, is Intel versus Intel.

Does the new Core i7 represent a significant step forward over the old king? The answer, inevitably, is yes and no. More specifically, it's a question of whether you're talking about stock frequencies or running overclocked.

The official numbers give the Core i7-3960X a nominal frequency of 3.33GHz, with a top Turbo speed of 3.9GHz. In our testing, it typically ran at 3.6GHz regardless of how many cores were heavily loaded.

Now, the fastest Gulftown processor is the 3.46GHz Core i7-990X.

In other words, the new i7 doesn't bring a major frequency boost. Nor does it add extra cores. So any performance advantage is going to be largely architectural.

For our yardstick, we've commandeered a Core i7-980X. It's slightly slower than the 990X at 3.33GHz, but the difference is pretty marginal. Kicking off with the x264 HD video encode test, it turns out that the new Core i7-3960X tears through at 49 frames per second while the old timer manages 43fps.

Elsewhere, it's a similar story. In Cinebenches R10 and 11.5, the Core i7-3960X achieves 27 seconds in the former and cranks out 10.54 points in the latter. The 980X's numbers are 32 seconds and 8.64 points.

In World in Conflict, which remains one of the most demanding games in terms of CPU load, it's 93fps for the Core i7-3960X and 88fps for the 980X.

All of this means the new chip is appreciably but not dramatically faster.

If you already had a 980X, you'd hardly feel compelled to upgrade.

Unless, that is, you compared the available overclocking headroom. Our 980X sample chip is capable of clocking up to just 3.9GHz. But in our testing, the new beast is good for 4.8GHz. And that's on plain old air cooling.

At that frequency, the Core i7-3960X is spewing out 63fps in the x264 HD video encode benchmark. At 3.9GHz, the 980X is good for 51fps.

Factor in overclocking, therefore, and the 3960X's performance advantage roughly doubles.


Intel core i7 3960x

What to make of Intel's new flagship processor and platform, the Intel Core i7-3960X?

On the one hand, it's clearly the fastest PC processing solution money can buy. By some metrics, such as memory bandwidth, it absolutely blows away even Intel's own six-core Gulftown processors such as the Core i7-980X.

It also brings a healthy improvement in overclocking headroom. We've little doubt that stable systems running at 5GHz or more will be possible with water cooling. Platform upgrades that include more PCI Express lanes and a faster SATA interface are also welcome.

However, in more realistic tests of application performance, the gap to Intel's outgoing flagship processor and platform is rather more prosaic.

What makes this frustrating is that the Core i7-3960X is very probably capable of the kind of massive performance boost we expect from a new high-end Intel processor.

Deep down, the specs don't lie.

Intel quotes the transistor count at 2.27 billion. That's nearly double the number of transistors in a Gulftown processor, despite the same nominal core count. Admittedly, the Core i7-3960X has 3MB of additional cache and a few more on-die features. But that's not enough to explain away all of the additional one-billion-plus transistors.

The explanation, of course, is that the Core i7-3960X is actually an eight-core processor with a pair of cores disabled.

When you're paying the thick end of £750, it's very hard to accept the idea that Intel is holding something back.

The question that immediately follows is whether there will be any scope for core unlocking, as with processors made by AMD. In our view, it's extremely unlikely. For that to be the case, Intel would have to be under extreme pressure from AMD.

In reality, the opposite is true.

The lack of Quick Sync is another downer. There are good architectural reasons why Quick Sync doesn't appear. But that's Intel's problem, not the customer's.

And customers of the Core i7-3960X have every right to expect full access to the product they've paid handsomely for.

We liked

If you want the fastest processor on the planet, look no further.

Most impressive is the additional overclocking headroom Intel has delivered over the old six-core chip. Platform upgrades including more PCI-E lanes and SATA 6Gbps are welcome, too.

We disliked

Simple, it's those hidden cores.

We want them switched on and we want them switched on now. Until that happens, the Core i7-3960X will remain a deeply, deeply unsatisfying chip, especially in the context of its sky-high pricing.

Final verdict

Ultimately, the reason why the Core i7-3960X looks like it does comes down as much to the performance of Intel's main competitor, AMD, as it does anything else.

Had AMD's new Bulldozer architecture been the game changer we had been hoping for, it's hard to imagine Intel would have released the Core i7-3960X with a pair of hidden cores. It would have run the full eight cores.

We feared AMD's ongoing inability to challenge at the top of the performance tables would eventually lead to Intel sand bagging. With the Core i7-3960X, it's finally happened. And that's a shame.

Intel Sandy Bridge E
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