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Eight cores. Two billion transistors. A radical modular architecture. 16MD of cache memory. And Turbo clockspeeds north of 4GHz. How could something that sounds so awesome end up so wrong. One day, the full story of AMD's troubled new PC processor architecture will emerge. It should make for a fascinating tale. After all, the Bulldozer architecture that underpins the FX 8150 must have seemed like a great idea. It's all about balancing threads with cores with a view to delivering the most efficient and effective processor architecture possible.

The relevant technology here is simultaneous multi-threading (SMT) or running more than one software thread in parallel on a single CPU core. Intel's take is Hyper-Threading. If you want to be really picky, you'd say Hyper-Threading was really a clever new take on sequential processing, not true SMT. But however you slice it, Hyper-Threading allows Intel to claim two threads per core and a multi-threading performance boost of around 15 to 20 percent-and therefore chip complexity and cost.

The aim with Bulldozer was to take SMT one step further and throw a few more resources at it. AMD came up with a module that contains a pair of integer units that share much of the remainder of what makes up a core. The result should have been a chip that gets near the performance of a true eight-core while being nearer in size and cost to a four-core CPU.

For now lets point in the direction of benchmark results. The 8150 doesn't get near the sort of performance you'd expect from an eight-core version of AMD's old Phenom II processor, much less anything Intel may release with eight cores. More to the point, Intel's six-core processors, old and new, absolutely hammer it while AMD's own six-core Phenom II X6 1100T is too close for comfort in threaded software and has it licked in terms of per-core performance.

Then there are Intel's four-core processor, including the new Core i7-2700K and, the Core i5-2500K. The 2700K has the edge across the board, as you might hope given its $39 price premium. Trickier to explain away is the 2500K, which is much cheaper than the FX 8150.

In highly threaded apps, the 2500K is off the place. But when it comes to games, the 8150's poor per-thread performance really hurts. All of which makes it a very tricky chip for AMD to market and a hard one to recommend. Overall, it's not terrible CPU and if highly threaded apps, such as video encoding are your bag, it's worth a look. However, that two billion transistor count makes it very expensive, while its disappointing performance puts a limit on the price tag AMD can attach. And more than anything else, it's just not a great chip for PC gaming.

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