CPUs

Review: Intel Core i7 3820

OverviewThis is a bit more within the reach of us mere mortals - a Sandy Bridge E CPU that doesn't cost the same amount as some full PCs.Intel, with even less of a fanfare than it made for the muted launch of the Sandy Bridge E platform, has now unleashed the quad-core iteration of its top-end chips, the Intel Core i7 3820, priced at £260 in the UK and $286 in the US. But, to be honest, we're not entirely sure why this CPU even exists.Before this, the cheapest Sandy Bridge E processor was the Intel Core i7 3930K, costing £450-500 in the UK and $650-700 in the US. The crazy expensive £800-900/$1,100-1,200 Intel Core i7 3960X takes its place at the top of the Intel CPU tech tree. Both those CPUs are full-blooded hex-core chips with Hyper-Threading tech enabling twelve threads of processing power.Except that they're not really hex-core chips at all. The Intel Core i7 3930K and i7 3960X are actually octo-core server chips with a couple of cores disabled to fit into the desktop segment.This, coupled with the huge price tag, has been our major bugbear with the latest of Intel's top-end chips. We now have eight-core CPUs potentially running in our home rigs, but unfortunately we're not allowed access to the disabled silicon sitting inside our incredibly expensive chips.A cynic would say Sandy Bridge E represents a great opportunity for Intel to sell broken Xeons to the desktop computing crowd for a tidy profit. Intel obviously refutes this, making the case that it believes the consumer would rather have higher clockspeeds over those extra cores, and it needed to sacrifice two cores to hit the 3.3GHz speed of the top chip.Before with the imminent release of its E5 Xeons, Intel has managed to hit 3.1GHz with a Sandy Bridge E-based server chip designed for the LGA 2011 socket.So what about the Intel Core i7 3820? Is this huge processor the same, is it really carrying around four dead cores in its innards? Little ghoulish really...Chip architectureThankfully, the Intel Core i7 3820 is not just another bust eight-core chip, this time with half its goodness turned off.The processor is actually a different die entirely, compared with bigger brothers the i7 3930K and i7 3960X. And they most definitely are bigger, by around 1 billion of the wee 32nm transistors.That gives the Intel Core i7 3820 1.27 billion in its make up. But that means it's still bigger than the previous generation's Gulftown hex-core CPUs, the entire Sandy Bridge lineup and even AMD's chunky quad-module Bulldozer chips.So the CPU die is rattling around in that massive LGA 2011 package, especially considering it's over 100mm2 smaller than the die size of the other two Sandy Bridge E processors.The Intel Core i7 3820's cache is also inevitably smaller than its Sandy Bridge E compadres, but compared with the Intel Core i7 3930K's 12MB you're only losing 2MB of L3 cache. At 10MB, the Intel Core i7 3820 is a little more cache-heavy than the 8MB-toting Intel Core i7 2600K and Intel Core i7 2700K chips.There is one other key difference between this straight Core i7 3820 and the X and K suffixed CPUs from Intel, and that's the unlocked nature of the other chips. This processor has a partially locked multiplier, which limits it to 43x compared to the 57x multiplier offered by both the other Sandy Bridge E chips and the top-end K-series i7 and i5 CPUs of the plain Sandy Bridge range.That ought to seriously limit its overclocking potential, but that's not necessarily the case.BenchmarksThe Core i7 3820 actually posts some decent scores but it's the Core i7 2700K that makes the best impression thanks to some stellar comparative benchmarks. In single-threaded applications the straight Sandy Bridge architecture has the edge in our test, showing why the gaming performance is higher as well.CPU performanceVideo encoding performanceGaming performancePerformanceThe Intel Core i7 3820 actually posts some decent scores in our benchmark tests, but it's the Intel Core i7 2700K that makes the best impression, thanks to some stellar comparative benchmarks. In single-threaded applications, the straight Sandy Bridge architecture has the edge in our test, showing why the gaming performance is higher as well.So the key battle for the Intel Core i7 3820 is the head-to-head with the Core i7 2700K, the top Sandy Bridge CPU. At £260, they're both priced in the same ballpark (or stadium, if you prefer), and at 3.6GHz vs the 2700K's 3.5GHz they're both around the same sort of clockspeed.Predictably things are pretty close in terms of raw performance. Importantly, though, not identical.The Intel Core i7 2700K still maintains a lead at stock clocks over the Sandy Bridge E Intel Core i7 3820. In single-threaded performance, the 2700K is actually quicker than even the i7 3830K, although despite having a higher clockspeed, the i7 3820 offers the same figures as the 3830K in single-threaded performance.Thanks to the extra couple of cores in the mid-range Sandy Bridge E chip, it takes a lead in the multi-threaded Cinebench rendering and X264 encoding tests. The resolutely quad-core Intel Core i7 3820 lags behind the hex-core chip and, interestingly, the lower-clocked Core i7 2700K, though.The straight Sandy Bridge's gaming pedigree comes to the fore, though, when we start throwing the World in Conflict and Shogun 2 benchmarks at the different chips.When the graphics card is taken out of the equation, in the WiC and Shogun 2 CPU DX9 CPU tests, the straight-line performance of the 2700K puts it ahead of both the Sandy Bridge E chips. And that's even true when we beat the i7 3820 with the overclocking stick, too.But the overclocking performance of the i7 3820 is quite interesting. Despite being only partially unlocked, meaning you hit the 4.3GHz limit straight away, you can push it further given the right motherboard.Thanks to the BCLK strap, the Sandy Bridge E chips are able to withstand a good tweaking of the base clock. That's still limited to being 100MHz, 125MHz, 166MHz and 250MHz, but it does give you some leeway.With a decent motherboard, you should be able to get up to the same sort of overclocking performance - around 4.7GHz - as the i7 2700K.That means that the partially locked multiplier really doesn't impact too much on the overclocking prowess of this new Sandy Bridge E chip.But the reliance on a decent motherboard is one thing that goes against the i7 3820, especially in a straight fight between it and the 2700K. And that's all down to platform costs.VerdictSo the Intel Core i7 3820 performs at around the same sort of levels as the top-end standard Sandy Bridge CPUs. We have to say, that's a bit of a disappointment.This is supposed to be the serious enthusiast processors for Intel's desktop faithful, but the more mainstream, soon-to-be-replaced Sandy Bridge setup is just as good at the quad-core level.On core-for-core performance, you're not getting much extra for your Sandy Bridge E money. Of course there are the extra PCIe lanes, which are useful if you're rocking more than two graphics cards, and the extra bandwidth offered by the new PCIe 3.0 tech, but the real value of that is still rather ephemeral at best.There are also the extra two channels of DDR3 memory in the Sandy Bridge E/X79 combo, but again for most of us the benefits of that extra bandwidth is rather difficult to gauge.In the overclocking stakes, the partially locked multiplier doesn't do the Intel Core i7 3820 a lot of harm, and you ought to be able to hit the same sort of OC numbers as the 2700K. But not best it.You need a decent motherboard to facilitate that, and that means spending nigh-on £200 on your board. Combined with the £260-odd you're paying for the chip, that still makes the Sandy Bridge E platform too expensive compared to the far cheaper base Sandy Bridge.There will be instances where the Intel Core i7 3820 and X79 combo will be beneficial, for the offline 3D rendering workstation or other serious productivity tasks that don't necessarily require heavy multi-threading. But that's a niche of an already minuscule niche.There's only one PCIe 3.0 graphics card out at the moment and the benefits that interface alone gives you are limited. And the extra memory bandwidth is only useful for a tiny minority of the world's populace.The fast majority of us, and all PC gamers, can already get enough all-round performance out of a standard Sandy Bridge setup.The quad-core Intel Core i7 2700K or 2600K are still the CPUs we'd recommend.We had hoped for a more impressive, compelling outing for the quad-core version of Sandy Bridge E. Sadly Intel already has the best-performing quad-core chip on the market, and as a whole platform the i7 2700K and Z68 chipset look like quite the bargain.The low price of the Intel Core i7 3820 is pleasing, though, and does mean that if you want to build the basis for an excellent workstation you can pick up a decently-priced CPU now and then splash the serious cash on a hex-core CPU if you can afford, or need, the extra cores at a later date.The socket will continue with 22nm Ivy Bridge E chips towards the end of the year, so there is at least some onward progression for the X79 chipset. Even if Ivy Bridge on the Z77 platform will put the boot into the i7 3820 in a couple of months time.We likedThe fact that Intel has put the chip out for the same price as the top-end Sandy Bridge i7 2700K is impressive, and thoroughly welcome. We're also pleased that the BCLK strap shenanigans help to render the partially locked multiplier a non-issue for the majority of overclockers.We dislikedSadly there's no real compelling reason to choose this CPU over the existing Sandy Bridge setups. We had hoped for at least a little bit of a performance lead for the extra cash you'd have to stump up for this platform as a whole, but sadly for the Intel Core i7 3820, the i7 2700K has it licked in most benchmarks.Final verdictIt's a decent chip, offering the extra bandwidth of the Sandy Bridge E platform for straight Sandy Bridge prices. But the vast majority of us don't need that bandwidth.

Read more: TechRadar

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