Core i7-3930K and Core i7-3820: Cheaper LGA 2011 - BeHardware
>> Processors

Written by Marc Prieur

Published on January 24, 2012


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When the LGA 2011 platform was introduced in November last year, we took the opportunity of testing the Core i7-3960X with its price tag of no less than $999. Thankfully, the i7-3960X isnít the only LGA 2011 processor around as Intel is now also offering the i7-3930K at $583 and an even more affordable model, the Core i7-3820, at $285.

Three CPUs for one platform
As this table shows, the Core i7-3930K has a slightly lower clock than the 3960X and a 12 MB rather than a 15 MB L3 cache. The i7-3820 stands alone with just four cores and a 10 MB L3 cache. Moreover, its multiplier is limited to x43, or 4 notches above Turbo mode, whereas the X and K models can go up to x57.

As we saw in the article on LGA 2011 however, the platform enables overclocking by the bus and this makes clocks upwards of 5 GHz accessible if required.

All the following tests were carried out using the same configuration as the one used in the report on the Core i7-3960X, with the AMD FX processors being tested here with the latest Windows 7 patches available.
Let's start, then, by looking at overclocking for these two processors. Remember on the i7-3960X we managed 4.6 GHz with the bios voltage fixed at 1.45v on the DX79SI motherboard. Now HWiNFO64 can give the vCore reading for the additional CHL8328 chip and we therefore also give this value in the table. We validated each clock for 15 minutes in Prime95 and the energy consumption given is that measured in load in this application.

To start with, the 3930K does better than the 3960X, with a bios voltage of only 1.4v (actually corresponding to 1.27v in load) required to clock it to 4.6 GHz. We managed to stabilise it at 4.7 GHz and we even managed to reach 4.8 GHz at 1.5v (actually 1.35v) though unfortunately at this voltage, energy consumption at the ATX12V exceeds 300 Watts and the Noctua NH-12UP SE2 no longer has sufficient cooling capacity. Note moreover that thereís a decent undervolting margin and that the 3930K can be overclocked quite easily up to 4.4 GHz.

The i7-3820 behaves similarly if we confine ourselves to the bios voltage, though the actual voltage applied to the processor is higher (the drop in voltage in comparison to the voltage requested in the bios being a function of the power requested). We managed to stabilise it at 4.7 GHz but not at 4.8 GHz. Beyond 4.3 GHz, we didnít overclock using the multiplier only, as this is locked at x43, but also the clock multiplier. Thus we managed 4.7 GHz (4697 MHz to be precise) using a x37 multiplier and a bus at 127 MHz (101.6 MHz x 1.25).

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Performance - Applications

Performance - Applications

[ Mental Ray ]  [ V-Ray ]  [ Visual Studio ]  [ MinGW/GCC ]  [ WinRAR ]  [ 7-Zip ]
[ x264 ]  [ MainConcept H.264 ]  [ Lightroom ]  [ Bibble ]  [ Fritz ]  [ Houdini ]

We started by looking at performance with applications. As expected, the gains offered by the 3960X over the 3930K arenít that high, varying between 2 and 4% in most cases. In Lightroom this advantage rises to 5% and then 8% in WinRAR and 7-Zip, benefitting from the additional 3 MB of cache.

The i7-3820 naturally suffers from having Ďjustí 4 cores and only gives slightly better performance than the Core i7-2600K. Note however there are some exceptions, with a 5% advantage in WinRAR and Fritz, a 5.7% advantage in 7-Zip and, most impressively, a 14.7% advantage in Lightroom, which greatly benefits from the memory bandwidth you get with DDR3 on four channels.

[ Standard ]  [ By performance ]

In the end, the i7-3820 is 4.5% faster than the 2600K on average, with the i7-3960X being on average 4.4% up on the i7-3930K.

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Performance Ė 3D games

Performance Ė 3D games

[ Crysis 2 ]  [ Arma II ]  [ Rise Of Flight ]  [ F1 2011 ]
[ TW Shogun 2 ]  [ Starcraft 2 ]  [ Anno 1404 ]

In contrast to applications, games are currently poorly optimised to take advantage of more than three or four cores. This means that the Core i7-2600K gives very similar performance to the Core i7-3820 and is even a little faster in some cases. In Arma II for example, the i7-3820 is 5% slower than the i7-2600K. We might ask if the lower bandwidth per thread on LGA 2011 than on LGA 1155 penalises it here.

The i7-3960X is also very close to the 3930K, with the smallest difference in Crysis 2 that seems to be limited by the GPU in this test (0%) and the biggest in Rise Of Flight (5.3%).

[ Standard ]  [ By performance ]

In the end the Core i7-3820 and Core i7-3930K come between the 2500K and 2600K. With a 3.9% advantage over the 3930K, the 3960X is the fastest processor in this area but the LGA 1155 CPUs carry the day when it comes to the bang you get for your buck.

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Energy consumption and efficiency

Energy consumption and efficiency
In our previous articles on processors, we measured energy consumption in load in Prime95. This stress test has the merit of pushing the various architectures to the limit in a pretty equitable manner, but we werenít able to use it to compare energy consumption and performance as the Prime95 benchmark consumes less and and isnít as balanced between processors.

We therefore decided to look for another application that would give us a level of performance and energy consumption representative of what we obtained on the other applications in our test protocol. In the end we opted for Fritz Chess Benchmark once again. In addition this application has the advantage of allowing us to fix the number of threads to be used easily.

The energy consumption readings therefore shouldn't be taken as absolute maximum values but rather as typical of a heavy load - applications specialised in processor stress such as Prime95 can consume up to 20% more. All energy economy features, including those on motherboards such as the ASUS EPU, were turned on for this test, as long as they didn't have a negative impact on performance:

[ 220V socket ]  [ ATX12V ]

At idle, the LGA 2011 platform is the most economical behind LGA 1155, and the Core i7-3820 and 3930K are no exception to the rule. In load the i7-3930K is fairly comparable to the 3960X, while the i7-3820 is a good deal more economical as of one thread. Note that in load, energy consumption at the socket increases by 5 Watts when you go from 2x4 GB to 4x4 GB, which has an impact on the LGA 1366 and 2011 platforms which are equipped with three or four bars compared to two bars for the others.

The reading at the ATX12V allows us to isolate processor consumption. Unfortunately however, the figures are not entirely comparable as in certain cases some of the CPU consumption is from the standard ATX 24 pin socket. To get a totally accurate comparison however, we can compare processors using the same motherboard.

We then looked at the energy efficiencies of the different processors. To get a representation of this you have to divide the performance levels obtained in Fritz Chess Benchmark by CPU energy consumption. The only problem is however that itís impossible to get an exact reading of CPU consumption: the readings at the ATX12V arenít 100% comparable from one platform to another and the reading at the socket doesnít allow us to isolate CPU consumption entirely.

We therefore decided to use two methods to isolate processor consumption:

- Energy consumption at the ATX12V
- 90% of the difference in energy consumption between load and idle at the socket

We took this at 90% so as to exclude power supply yield. Note that while the first reading favours processors that draw a small proportion of power from the standard ATX socket, the second favours those with high energy consumption at idle. Unfortunately no method is perfect.

[ 220V socket ]  [ ATX12V ]

Whatever the technology used, the Core i7-3960X and 3930X have very similar energy profiles. These processors are not however the most economical, especially on one thread. The Core i7-3820 does a good deal better here but itís still behind the LGA 1155 processors.

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As expected, given its spec, the Core i7-3930K makes the Core i7-3960X entirely dispensable. Why spend an extra Ä350 or Ä400 for such a small gain in performance (between 4 and 5%)?

The Core i7-3930K is therefore a choice cut for anyone looking for a very high end solution but it shouldn't be forgotten that its full potential can only be seen on applications that can exploit all six cores or during intensive multitasking!

Such a processor is for example of no advantage in games given the current state of their graphics engines. On the downside, apart from its price, which is still rather high, it isnít yet widely available.

For its part, the Core i7-3820 has a rather odd positioning. It certainly makes the LGA 2011 platform even more affordable, as it should be available for under Ä300 when it appears on the shelves in a few weeks. It is however only a quad core processor and therefore offers little more than the Core i7-2600K. Of course, it will be a bit cheaper (official prices of $285 and $317 respectively), but this will only partially compensate the user for the higher costs of the platform.

It's therefore only worth going for to gain access to the possibilities that are exclusive to LGA 2011, namely PCI-Express 3.0 (while waiting for Ivy Bridge to come on stream on LGA 1155 in April), effective support for 3 to 4 graphics cards, memory on four channels, support for more than 32 GB of memory.

These options may be of interest for certain specific applications but wonít be of use to the large majority of users, who would be best advised to stay on LGA 1155.

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