AMD Phenom X4 review

AMD had a hard time of it in 2007, and it was no surprise when the company was forced to announce lay-offs earlier this month. Part of the problem was its Phenom quad-core processors, which were dogged by production delays and architectural bugs, and outgunned by Intel's rival CPUs - as you'll see in the current issue of PC Pro, on sale now.

But now, just too late for inclusion in that Labs, the company has delivered samples of an updated range of Phenoms, renamed Phenom X4 to distinguish them from the forthcoming triple-core versions.

The new designs are still based on the 65nm Agena core, with their B3 revision number indicating only minor changes from the original B2 stepping.

The 9550 and 9650 models run at the same speeds as the 9500 and 9600 parts they replace - 2.2GHz and 2.3GHz respectively, with an effective HyperTransport frequency of 3.6GHz. Cache size remains the same, with each core having its own 512KB L2 cache and access to a shared 2MB L3 buffer. TDP is unchanged too at 95W.

The new crop also introduces two new faster models: the 9750 and 9850, clocked at 2.4GHz and 2.5GHz. The 9750 is effectively just a faster 9650, but the 9850 is a multiplier-unlocked "Black Edition", enabling overclockers to push the chip as far as they like.

It's also AMD's first chip to support an effective 4.0GHz HyperTransport. This raises TDP to 125W, despite using the same core as the lesser models.

These modest increases in clock speed don't promise a great leap in performance, but when we put the new models to the test we found overall benchmark scores had actually risen dramatically.

While the old 9500 scored 1.23, the new 9550 achieved 1.39 - a 13 percent increase; the 9650 scores 1.45, against the older 9600's 1.28 - 13 percent up again. The 9750 clocks in at 1.50, and the top-end 9850 roars up to 1.55.

As the graph below shows (click on the thumbnail to get a better view), scores like this have, until now, only been attainable by Intel's high-end parts - and at higher prices.

But this improvement isn't down to any great engineering breakthrough. It merely reflects that the earlier models were never able to achieve their full potential.

The problem is a bug in the core logic of the older Phenoms - the notorious "TLB erratum". To ensure that these parts run stably, the BIOS has to disable a faulty caching function, slowing down the system. The new B3 silicon fixes this bug, letting the core finally attain peak performance.

So, after a disappointing start, the Phenom has finally found its feet. The old parts were a letdown, but the new revisions make a real splash, delivering a lot of bang for comparatively little buck. They make almost every Core 2 Duo E6000 and E8000 processor look redundant - after all, why buy dual-core when you can get quad-core for the same money?

It's a fair bet that AMD's claim on the high ground won't go unchallenged for long. Intel won't like this encroachment onto what has hitherto been its sole territory, and with its 45nm process and vast resources it's well positioned to respond decisively.

But nothing can change the fact that AMD has finally landed a punch, producing a realistic competitor to Intel's high-end desktop CPUs. That's great news for consumers, and AMD will doubtless be hoping it gives their corporate fortunes a lift as well.

Author: Darien Graham-Smith