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Intel Core-i7 3960X, X79 Express and LGA 2011
by Marc Prieur
Published on December 26, 2011

The first Nehalem architecture Intel Core i7s were introduced on a high-end platform, LGA 1366, in November 2008, before being rolled out for the mid-range in 2009 on LGA 1156.

With Sandy Bridge, Intel has done things the other way around and LGA 1155 became available ten months ago with the higher-end roll out only coming on LGA 2011 now. Better late than never?
Core i7 LGA 2011: A cut down Sandy Bridge-E
The Core i7 LGA 2011s use a new chip, codename Sandy Bridge-E. Designed for the Xeons, this chip has no fewer than eight cores and 20 MB of L3 cache on a 2.27 billion transistor die. The die has a large surface area of 435mm², which is a little more than double that of a Sandy Bridge with its IGP (not included here).

In comparison to the Sandy Bridge LGA 1155, the Sandy Bridge-E LGA 2011 spec is as follows:

- 8 cores instead of 4
- 20 MB of L3 cache instead of 8 MB
- 40 PCI-Express lanes instead of 16
- 4 DDR3 channels instead of 2

While the prospect of 8 cores and 20 MB of L3 may be mouthwatering, you can wipe away your saliva as no Core i7 will actually be sold with this configuration. At best, we’ll have 6 cores and 15 MB of L3, with the 8 core / 20 MB versions reserved for the forthcoming Xeon E5s, which will be more expensive (up to $2000). Intel is, then, recycling the partially defective SNB-E dies, which will be numerous given its size, as Core i7 LGA 2011s.

The other major difference is of course the more extensive PCI-Express support. Here 40 lanes are available to the processors themselves and they can be used as follows:

- 2x16 and 1x8
- 1x16 and 3x8
- 1x16, 2x8 and 2x4

With two graphics cards there isn’t that much of a gap with the LGA 1155 platform, with the difference between 2x16 and 2x8 being quite low in practice. For 3-way and 4-way multi-GPU systems however, LGA 2011, as LGA 1366 and AM3+ with the 990FX chipset, has an advantage even if the existence of LGA 1155 motherboards with an NVIDIA or LucidLogix PCI-Express switch means that most of the platform's inherent limitations can be compensated.

Note that although the LGA 2011 processors and motherboards have been designed for PCI Express 3.0, for the time being, while awaiting the necessary certification, Intel is only indicating PCI Express 2.0 compatibility.

Finally, there’s now quad-channel DDR3 support, which doubles the theoretical bandwidth available on LGA 1155 and increases it 33% in comparison to LGA 1366. Officially this memory is DDR3-1600 / PC3-12800 type, but ratios allowing for DDR3-1866, 2133 and 2400 are available.

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