Intel's Core i7 range now resides on two different platforms, not only confusing the Hell out of less-well-informed PC buyers but also making the choice of which platform to opt for much more difficult. On the original 1366-pin home of the Core i7 the entry level chip remains the 920, which boasts a default clock speed of 2.66 GHz. For only a few pounds more, however, you can now get hold of a Core i7 860, which runs at a noticeably faster 2.83 GHz and enjoys considerably cheaper motherboard costs.

As with its Core i5 brethren the new Socket 1156 i7 860 uses a conventional dual-channel memory controller. This is in contrast with the triple-channel 920 and means you'll be back to the traditional 4GB or 8GB configurations rather than the unorthodox 6GB or 12GB choices of socket 1366.

In actual use this difference isn't nearly as pronounced as you might think, as most applications just don't make use of all that spare bandwidth. Both chips support HyperThreading which allows each core to process two threads simultaneously (a feature cut from the i5), and both have comparable transistor counts, despite the 920 featuring an extra memory channel. This is because Intel has moved the PCI Express interface onto the chip itself in all socket 1156 chips, allowing the video card to access the processor directly without the need for a traditional Northbridge.

This decision has a number of knock-on effects. Firstly, the P55 motherboards of socket 1156 solutions require only a single Southbridge chip to handle USB, SATA and PCI Express 1x buses, making them a lot cheaper. Secondly it means the 1156 platform has only a single 16x bus, putting it at a significant disadvantage in setups with multiple graphics cards.

Whilst X58 solutions can provide a full 16x lane to two or even three video cards, on P55 alternatives the single on-chip 16x PCI Express lane must be split into two 8x lanes. This has only a slight effect on cards like the GeForce GTX 260 or Radeon 4870, but move upwards to flagships like the 5870 or GTX 295 and the difference can be as much as 30 percent, a situation that will only become worse as faster cards are introduced. It could also be a major cause for concern when 6Gb/s SATA and USB 3.0 technologies become more important, as both of these demand more bandwidth than the P55 alone can provide.

The final effect of the on-chip PCI Express controller is a reduction in overclocking ability. Although you can still reach the dizzy heights of 3.8GHz to 4.0GHz on a good i7 860, the 1156 platform will make you work much harder for your MHz. The unlocked PCI Express speed will result in certain base clock frequencies being strangely less stable than faster ones, whilst the overall ceiling is a good 2-300MHz lower than that of the i7 920. The 1156 chips also demand a lot more voltage to run at higher speeds, though this is less of an issue as they also run significantly cooler.

So far it sounds like bad news for the 1156 platform, but the 860 has a trick up its sleeve; a greatly improved turbo mode. Turbo mode is a feature introduced in the original Core i7 which allows the chip to jack up the multiplier when running at suitably cool temperatures. When using only one or two cores the multiplier can increase further still, resulting in even higher performance.

This functionality has been ported to the newer chips, but its implementation is now much more aggressive. 1156 chips can completely turn off cores that are lying fallow, greatly reducing power output and therefore temperature. This in turn allows Intel to be much more confident with the Turbo frequencies than it was before, as shown by the table below.

Core i7 920, Core i7 860 Default multiplier (clock speed)20 (2.66 GHz)21 (2.8 GHz)
All Cores Turbo (clock speed)21 (2.8 GHz)23 (3.06 GHz)
1-2 Cores Turbo (clock speed)22 (2.93 GHz)26 (3.46 GHz)

This means that for stock speed users, the i7 860 can provide significantly better performance, particularly when fewer than three cores are being used. This intelligent core handling also provides considerably better power consumption numbers, as the 860 will drop its clock frequency to just 1.2 GHz when idle; providing, of course, you have the relevant features enabled in both the BIOS and Windows.

The final differentiation between the two sockets is that of upgrade potential. By opting for a small 775-sized chip package, Intel has effectively limited the 1156 platform to 4 cores until manufacturing processes shrink significantly. With “merely” dual channel memory, 1156 is also less well-equipped to handle extra cores than 1366.

The latter platform already has 6 and 8 core chips announced and set to arrive in 2010, so if you fancy a broader range of upgrade options you should certainly opt for the 920 processor and a suitable board, even if the initial outlay is a little higher.

Verdict
All in all we'd have to still recommend socket 1366 to buyers with a larger budget. The extra PCI Express lanes will become increasingly important, whilst the superior upgrade path and better overclockability provide tangible benefits right now. 1156 is still highly desirable for the mainstream market, though we think the i5 line of chips is arguably a better fit for this sort of user.

Company: Intel

Contact: 0870 607 2439

Tags: hyperthreading intel core i7 universal serial bus pci express intel core i5 hardware intel corporation hertz