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Four Cores for LGA 2011: Highs and Lows

Even if we put aside the outdated desktop platforms that currently already include LGA 1366 and LGA 1156, Intel’s high-end Core i7 processor lineup won’t be monotonous at all. Intel currently offers six- as well as quad-core processors under the Core i7 brand name. Moreover, they may belong to the mainstream LGA 1156 as well as high-end LGA 2011 platform. In fact, there are only two parameters that are the same for all today’s Core i7 processors: all of them are faster than Core i5 and their prices fall into the $250+ range.

The following table lists the specifications of all current desktop Core i7 CPU models:

As we can see, this lineup includes six-core Sandy Bridge-E processors available only in LGA 2011 form-factor, a new quad-core Core i7-3820 for LGA 2011 systems and the well-familiar Sandy Bridge processors for LGA 1155 platforms. It is extremely interesting to see what place the new quad-core LGA 2011 processor will find in the market, while being in this company. It boasts slightly better characteristics than Core i7-2700K: its frequency is 100 MHz higher, its L3 cache is larger, it supports four memory channels, and despite all that Core i7-3820 is even a little cheaper than its LGA 1155 brothers.

However, the catch here is in the price of other LGA 2011 system components, mainboards in the first place. For illustration purposes we compared side by side  the prices on several popular mainboards from Asus and Gigabyte with similar characteristics designed for LGA 2011 and LGA 1155 platforms (the table below shows the Newegg online store prices as of January 28, 2012):

LGA 1155 LGA 2011
ASUS P8Z68-V/GEN3 - $180
Gigabyte Z68XP-UD3P - $175
ASUS P9X79 - $280
Gigabyte X79-UD3 - $270
ASUS P8Z68-V PRO/GEN3 - $205
Gigabyte Z68XP-UD4 - $195
ASUS P9X79 PRO - $330
Gigabyte X79-UD5 - $325
ASUS P8Z68 DELUXE/GEN3 - $255 ASUS P9X79 DELUXE - $380
ASUS Maximus IV Extreme-Z - $340 ASUS Rampage IV Extreme - $450

LGA 2011 mainboards are about $100 more expensive, which brings the price of a complete platform built around Core i7-3820 way beyond the price of a similar system built around LGA 1155 Core i7 processor.

Moreover, when we take a closer look at Core i7-3820, we uncover a few other drawbacks. Since this processor is based on Sandy Bridge-E design, it is based on a more complex semiconductor die. Luckily, Intel designed a separate semiconductor die with four cores for the quad-core LGA 2011 processors. However, the large L3 cache, the QPI controller required for server applications and more complex memory and PCI Express bus controllers made the transistor count of the quad-core Sandy Bridge-E processor about 25% larger. No wonder that the calculated TDP of the quad-core LGA 2011 processor, just like that of its six-core brothers, is set at 130 W and not at 95 W as it is for the LGA 1155 Sandy Bridge processors. In other words, Core i7-3820 is not as energy-efficient as Core i7-2500K or Core i7-2600K.

Just like other LGA 2011 processors, Core i7-3820 doesn’t have an integrated graphics core, and therefore it doesn’t support Quick Sync technology, which comes in very handy during non-professional work with video content.

Another feature inherited from Sandy Bridge-E is a slower L3 cache than the one in regular Sandy Bridge processors. It has higher 20-way associativity, which causes its latency to increase, as we have already seen in our previous article. Although in this case the chances that certain data is in fact available in the cache-memory are certainly higher, and larger memory size also contributes to it.

But what is particularly upsetting is that Core i7-3820 doesn’t belong to the overclocker K-series, which means that it will have limited potential in terms of clock frequency multiplier increase. The highest multiplier this processor supports is 43x. Core i7-2700K and Core i7-2600K processors for LGA 1155 systems, just like the six-core LGA 2011 CPUs, do not have any similar restrictions.

The only thing that Core i7-3820 can set off against all this is the increased number of PCI Express lanes, which now equals 40, and four memory channels. However, taking into account that graphics sub-systems built of multiple graphics accelerators are usually of interest only to a limited number of gaming fans, and quad-channel memory doesn’t deliver any significant advantages, we start having serious doubts about the benefits of the newcomer for the end-users. However, there is one thing that could save the day. It is…

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