AMD FX “Bulldozer” review

Mike Jennings Read more October 18, 2011

Image 1 of 5

£162

Price when reviewed

It took AMD a long time to bring it to market, but Bulldozer is finally here to offer Intel’s all-conquering Sandy Bridge chips some much-needed competition. That’s AMD’s intention, anyway.

Bulldozer is henceforth to be known as AMD FX: the new range consists of four chips, from the £95 FX-4100 to the high-end, £195 FX-8150, and they share a brand new 32nm, socket AM3+ architecture.

AMD FX

AMD’s headline innovation is what it calls “Bulldozer Modules” – processor cores containing two physical execution units, and hence able to service two threads simultaneously. Each module features only a single shared pipeline, and a single floating-point arithmetic unit, so it’s not a fully dual-core design – but it should still deliver greater parallel throughput than one of Intel’s Hyper-Threading cores, which offer only a single execution unit.

In practice, it means AMD’s top-end FX-8150, with four modules, can process eight threads at once, bringing it into line with the best Intel chips. The cheaper FX-6100 has three modules serving six threads, and the FX-4100 has two modules to process four threads.

On the top-end CPUs you get 2MB of L2 cache per module, shared between execution units, and each unit has its own L1 cache, scheduler and memory bandwidth. 8MB of L3 cache is shared across the whole chip.

AMD FX

AMD claims its new architecture allows each core to be more efficient at multitasking, and it’s loaded the FX chips with a host of other improved features too. Turbo Core has been given a shot in the arm: last year’s models could only overclock half of their cores, but now every core in an FX chip is capable of boosting by up to 300MHz.

That’s less additional juice than before, but spread across more cores, which makes sense given AMD’s focus on multi-threaded performance. Turbo Core also now includes a Max Turbo mode which boosts the clock further, but only across half a chip’s cores: the FX-8150, for instance, will now be able to run four of its 3.6GHz cores at a tasty 4.2GHz.

That’s a bigger boost than you’ll see from Intel, which uses Turbo Boost to overclock its Core i5-2500K from 3.3GHz to 3.7GHz, and its i7-2600K from 3.4GHz to 3.8GHz.

Every chip in the new AMD range is unlocked for easy overclocking, and they’re all set up to handle dual-channel DDR3 memory running at up to 1,866MHz – an improvement over the 1,333MHz the old Phenom II could handle. Here, FX outstrips Sandy Bridge again, with the latter only officially handling up to 1,600MHz memory.

Top-end power requirements stay the same, with the most demanding chips possessing a TDP of 125W. AMD has introduced a new socket for its new CPUs, dubbed AM3+, but you might not need to upgrade: AMD’s FX chips are backwards-compatible with older AM3 boards with a BIOS update. Which motherboard manufacturers actually provide these, however, remains to be seen.

On paper, these new cores, running at these high speeds, look like they might just be capable of challenging Intel’s dominance.

To find out, we plugged the top-of-the-range FX-8150 into our test rig – an Asus Crosshair V Formula motherboard, AMD Radeon HD 6870 graphics card, 4GB of RAM and a 500GB Samsung Spinpoint F3 hard disk – and launched our real-world application benchmarks.

The system achieved an overall score of 0.84. That’s the kind of performance we’d expect from a low-end Core i5 chip. A recent PC from Advent with a 2.9GHz Intel Core i5-2310 returned the same 0.84 score in our benchmark, with a stock-speed Core i7-2600 serving as the benchmark at 1.

AMD FX

In our test rig, the idle and maximum power draws hit 91W and 224W, which is nothing out of the ordinary. And the FX chip is certainly cool enough: when idling beneath our Zalman CNPS7X cooler it hit just 22 degrees, rising to 55 degrees when stressed with Prime95.

Theoretically, that suggests AMD’s new chips might have plenty of scope for overclocking, but in our tests we were only able to get the system up to 4.2GHz: not a big enough leap to worry Intel.

That isn’t the end of the bad news. AMD used to be known as the budget choice but the FX-8150 offers poor value compared to Intel. This top-end CPU will sell for £195 inc VAT, £35 more than the faster Core i5-2500K. The situation seemingly improves lower down the range, with the FX-4100 coming in at just £95 inc VAT but, as we haven’t the opportunity to test it yet, we’ll reserve judgement.

AMD made us wait for Bulldozer, but on the evidence of this first outing we can’t say it’s been worth it. It’s not as fast as its direct rivals, yet will cost you more. When it comes to desktop processors, Intel still holds all the cards.