Feature Articles

Changing for the Future - Intel's Core i7

Changing for the Future - Intel's Core i7



Intel's X58 Express Chipset

Intel's X58 Express Chipset

With such a radical change as integrating the memory controller onto the CPU, a completely new chipset and a new socket, LGA1366 is required for the Core i7. The answer from Intel is the X58 Express chipset. The first thing you may notice on any X58 board is the odd number of DIMM slots, reflecting its triple channel memory support. The traditional Northbridge has been removed since there's no need for it anymore with QPI and the integrated memory controller but there is still another hub, the IOH, which primarily provides the 32 PCIe 2.0 lanes for graphics cards. The Southbridge remains and it is the now familiar ICH10R, which will support up to 6 SATA 3.0Gbps ports and 12 USB 2.0 ports as a start.

The chipset supports up to two 16-lane PCIe graphics slots (ver 2.0) and communicates with the processor via the QPI bus (routed through the IOH). Retail versions are likely to come with more than two PCIe 2.0 x 16 slots and besides the native CrossFireX support, third party vendors can also get their boards certified to work with SLI configurations, making the X58 the only widely available chipset to support both competing multi-graphics technology.

While the chipset may not seem unfamiliar to enthusiasts, the front side bus (FSB) as we know it is no more. A base clock of 133MHz is now the underlying clock that is followed by all the other components like memory and CPU, after applying a suitable multiplier to it of course. Generally, there are 4 such multipliers, though you may not get the option to tweak all 4 inside the BIOS.

First, the CPU speed is defined by multiplying the base 133MH to a clock ratio. This can be applied to each of the active CPU cores on the Core i7, e.g. 4 different ratios for a quad-core Core i7. So far, the unlocked Extreme Edition i7-965 that we have has a range of between 20 - 35 for the multiplier, giving it a resultant CPU frequency of 2.66 to 4.66GHz. This is hence the most crucial multiplier for enthusiasts.

The memory speed is also governed by its own memory multiplier, which is similarly derived from the base clock and this multiplier. Next, one can adjust the QPI rate and the uncore, which the latter limited with a distinct relationship of twice the memory multiplier value.

Overclocking the Core i7

So how does one go about changing the CPU frequency now that the familiar FSB is no more? Well it is actually much of the same and the user has a choice of either increasing the CPU multiplier or the base clock frequency (default of 133MHz) or both. Also, remember that the new Turbo Mode option gives users the flexibility of setting upper limits for the CPU multipliers for a 1-core, 2-core, 3-core setup, up to the maximum number of active CPU cores available. So if your applications are mostly dual threaded, you can opt to have a more aggressive 2-core CPU multiplier for a higher clock speed and more modest clocks for the 4-core configuration. Unfortunately the full Turbo mode goodness is restricted to the Extreme Edition while a more restricted version is available on the Core i7-940 and i7-920 models where one can't set values higher than two speed bins (each speed bin just means a 1x increase in CPU multiplier).

After this, it's a matter of trying various clock ratios and testing the system for stability. Getting the right version of CPU-Z is also useful in knowing the success of the overclock. In our example below, we're running it at the stock settings.

Of course, one can also increase the base 133MHz clock. This is done by increasing the 'Host Clock Frequency Override' setting in the reference Intel BIOS, though it could be labeled differently on retail boards. Since this base clock is used for memory clocks too, one should be careful to adjust the memory multiplier to ensure that the memory is not getting overclocked inadvertently.

As for tuning the memory, let us first repeat Intel's warning that memory exceeding 1.6V could damage the Core i7. As for the memory timings, it's quite straightforward and similar to that on the Core 2, with Intel's XMP memory profiles perhaps the easiest way to get the approved 'overclocked' settings for a particular memory kit. Again, the base 133MHz clock is key, so you can increase the multiplier slowly to get a higher resultant memory frequency or just increase the base clock. There may also be a need to increase the QPI voltage here since the UCLK multiplier may be increased (due to the requirement that it be 2x the memory multiplier).

For actual overclocking performance expectations, we'll be showing you that quite soon in a follow-up article.