AMD Phenom II X4 965 Black Edition review

For the most part, we think you'd agree, walls are good things.

They do all kinds of useful little jobs. Like holding up your roof, keeping the wind out and dulling the noise from your bickering neighbours and their ASBO-generating kids. But did you know that CPUs also have walls?

OK, we're only talking metaphorically. But a wall is the best way of thinking about the thermal limits of any given CPU. And like real walls, thermal walls are best avoided at high speeds. At this stage, you might be wondering what all this has to do with AMD's latest speed bump of its 45nm Phenom II X4 processor, the 3.4GHz 965 Black Edition.

Well, there's a bit more to this story yet. So bear with us, it will all make sense in the end.

You see, the lives of most CPU designs tend to follow a similar path. The longer they're on sale, the more mature the underlying architecture becomes. Tweaks are made here and there to improve the likes of efficiency and clockability. Big gains tend to be made at first followed by diminishing returns as room for improvement decreases.

Consequently, the gap between the most expensive examples of a given CPU design and the cheapest ones tends to shrink over time.

By the time a chip family is ready to drop off the price lists, the budget variants are often capable of pretty much the same overclocked frequencies as the most expensive. They all hit that annoying wall at the same speed, in other words.

When it comes to AMD's 45nm Phenom II X4 chips, it seems the big gains have already been made. The new 965 BE runs just 200MHz faster than its predecessor, the 955 Black Edition. If that's sounds pretty undramatic, it delivers even less additional overclocking headroom.

If our test chip is anything to go by, 3.7GHz is the best you can hope for using stock voltages. That's just 100MHz better than the 955.

With that kind of incremental increase, it seems likely that there's not much more to come from AMD's 45nm family of processors in terms of clockability. Of course, speeds well in excess of 3.7GHz are possible with fancy cooling and tweaked voltages.

Problem is, voltage tweakery is a bit of a black art at the best of times. Moreover, Intel's 2.66GHz Core i7 processor will hit a heady 3.9GHz on stock voltages, proving that it's possible to achieve great results with zero overclocking skills.

Having said all that, we still prefer AMD's simpler platform proposition. With the arrival of Intel's Lynnfield CPU (see page xx for our in-depth analysis), Intel has introduced yet another new socket.

Meanwhile, AMD has gone to great lengths to maintain compatibility, both backwards and forwards. We just wish its CPUs were a tiny bit faster.

Follow TechRadar reviews on Twitter: http://twitter.com/techradarreview