10 months after launching on the LGA1366 platform, Intel has decided to roll out its Nehalem architecture on the new LGA1156 platform, supposed taking it mainstream. What changes does it bring and what do they mean in practice?
A new platform
The first difference comes with the socket, down from 1366 to 1156 contact points as a result of various modifications that we’ll go into further down. Whenever a new socket comes out, it seems a new fan is also called for and it doesn’t seem unreasonable to wonder at the rationale for all this. If you measure the difference between the mounting holes in recent Intel sockets, you find:
- LGA775: 72 mm
- LGA1156: 75 mm
- LGA1366: 80 mm
We have to say, we’re somewhat mystified as the fact that the LGA1156 socket is compatible with neither of the others suits nobody except cooler designers – although even some of these, like Noctua, will be offering free adaptors to their users.
The other innovation, harder to spot, is the integration of the Northbridge in the processor, which means the die goes from 263 to 296mm² and the number of transistors from 731 to 774 million. Socket LGA1366 constituted a first step for Intel with the integration of a triple-channel DDR3 memory controller and LGA1156 continues on this route with a double-channel DDR3 memory controller. In practice, the absence of the third channel won’t be missed as it only offered very limited, even inexistant gains because the increased bandwidth wasn’t always big enough to make up for higher latency.
Integration of the PCI-E controller onto the processor itself is a real improvement, especially as it is linked internally to the memory controller by a QPI type bus. It supports 16 PCI-E 2.0 lanes and can supply 1 x16 slot or 2 x8 slots in a multi GPU configuration. On LGA1366 the PCI-Express was supported by the X58 with a total of 36 lanes. When you think that a multi GPU configuration isn’t much affected whether working at 2x8 or 2x16, what some users will regret is the absence of a 3rd or 4th x8 slot.
As with the X58, the P55 allows CrossFire configurations as well as SLI configurations as long as the motherboard is compatible, in other words a card for which the manufacturer has paid NVIDIA for a license…
The complete integration of the northbridge within the processor leads to a greater simplification in the design of motherboards as the P55 Express chipset designed for the LGA1156 is in fact just a “Super ICH10” with a couple of extra PCI-Express lanes to make a total of 8. These still function at 2.5 GT/s (as against 5 GT/s for those in the CPU) or 250 MB/s per lane in each direction.
As the Northbridge is completely integrated on the processor, connection to the chipset via a QPI bus is no longer necessary and this simplifies motherboard design. Instead you’ll find the usual DMI bus linking the MCH and ICH but still limited to 2 GB/s which is a bit low if only because 8x PCI-E total 4 GB/s.
