Intel Core 2 Extreme X6800 review

We've always been a big fan of Intel's mobile processors, particularly the Core Duos.

Well priced, efficient and powerful, they're everything a processor should be. So we were excited to get Intel's new desktop processors, the 2.66GHz Core 2 Duo E6700 and 2.93GHz Core 2 Extreme X6800, as these are based on the same technology used by the Core Duo.

The new processors spell the end of Intel's Netburst architecture, which the Pentium 4 used; although the new processors have their own micro-architecture, they use technology that has evolved from the Pentium III. The Core 2 micro-architecture is designed to offer faster processing speeds by being more efficient. The Pentium 4 tried to improve performance by pushing clock frequencies, which resulted in unacceptable heat, noise from cooling fans and higher power requirements.

With Core 2, Intel has focused on reducing the clock speed in order to reduce heat, power requirements and, ultimately, noise. The Core 2 Duo E6700 has a thermal design power (TDP) of just 65W, while the X6800 has a TDP of 75W; this is a massive decrease from the Pentium 4 960's TDP of 130W. The problem with reducing the clock speed is working out how to make the processor faster than its predecessor. It's here Intel has worked its real magic. First, the processor's execution pipeline has been improved so that on average it can execute more instructions per clock cycle; in short, the Core 2 processors can do more work at lower clock speeds.

Processors try to save time by predicting when a program will jump to a different set of instructions (a branch) and working on those instructions in advance. While a correct prediction speeds things up, an incorrect one means the instruction pipeline has to be cleared and restarted. With the Pentium 4, its deep 31-step pipeline took a long time to clear after an incorrect branch prediction; the Core 2 processors have a 14-step pipeline, which is quicker to clear and refill.

Next, the Core 2 architecture introduces the Smartcache technology. Both the processors reviewed have 4MB Level 2 caches, but some of the lower-speed Core 2 Duos have only 2MB. The cache is intelligently shared between two cores. For example, if you run a single-threaded application that can use only a single core, that core gets the full 4MB. In addition, if both cores need to access to the same data, they can share the cache memory rather than having to load the data into the cache twice.

The cache helps to reduce the main bottleneck in Intel's processor design: memory access. While AMD integrates its memory controller into the processor, providing direct access to memory, Intel uses a separate memory controller on the motherboard's Northbridge. The link to the memory is shared and can be the cause of bottlenecks. With the Core 2, though, Intel's Smart memory access means data from memory can be loaded into the Level 2 cache just before it's needed. It's not quite as efficient as an integrated memory controller, but it goes some way to making up ground. Finally, all but the cheapest Core 2 processors have 1,066MHz front side buses and support for DDR2 800MHz memory, increasing general system performance and speeding memory access.

The new processors are all LGA775, but you'll need a motherboard with a 965 or 975 chipset to use the processor. If you've bought a 975 motherboard recently, you should check the manufacturer's website for compatibility, as not all boards have the correct power requirements for the Core 2 processors. The current range of processors includes the Core 2 Duos, which range from a clock speed of 1.6GHz to the 2.66GHz E6700 reviewed here. There is currently only one model in the Extreme series, the X6800. While Intel's previous generation of Extreme processors had faster front side bus speeds and more cache, the Core 2 version has a faster clock speed. It's also multiplier unlocked, so you'll find that it can be overclocked easily.