AMD Phenom X4 9850 BE review

The launch of the original Phenom X4 quad-core processor was blighted by a hardware bug and disappointing clockspeeds. Can the new Phenom X4 9850 Black Edition and its revised B3 stepping salvage the situation for AMD?

It's hard to know just how much AMD has been hurting following the frankly disastrous introduction of its quad-core CPU architecture. But here's one metric of its current predicament that is rather revealing. Back in 2005 AMD's entry-level dual-core chip, the relatively feeble Athlon 64 X2 3800+, commanded a £275 sticker. Today, the brand new Phenom X4 9850 Black Edition flagship quad-core model is priced to sell at £155.

Phenom's weakness

And lest you have forgotten, Phenom is a big old beast that must surely be costly to manufacture. All four cores, plus a memory controller, HyperTransport I/O and 3MB of cache memory are packed into a single 65nm processor die. Making matters worse, AMD has been having difficulty clocking the chip up to competitive speeds. Despite claims to the contrary, therefore, we suspect the upcoming triple-core Phenom X3 model is an attempt to lift production yields out of the trash can.

Intel's latest quads, by contrast, are composed of a pair of dual-core dies and are built using finer 45nm production technology. Thanks to the great per-cycle performance of the Core 2 architecture, Intel also has the luxury of not needing to push its chips to limit in terms of clockspeeds. All of which takes the pressure off yields as a whole for the stupidly successful Core 2 family.

But back to the matter at hand, namely the new Phenom X4 9850 Black Edition. Arguably the most significant aspect of this new chip, which benefits from the new B3 stepping of AMD's quad-core architecture, is the removal of the nasty little TLB bug.

TLB bug is gone...

As we've reported on numerous occasions, the TLB bug is a hardware erratum effecting the chip's translation lookaside buffer. In certain scenarios, it can cause systems to fully lock up. In reality, that's likely to be an extremely rare occurrence. But the mere possibility forced AMD to create a BIOS-based work around that disabled the faulty circuitry.

You might think that was problem solved. But in testing the BIOS fix compromised performance by around 10 per cent on average and as much as 30 per cent in isolated benchmarks. With Phenom struggling to reach competitive and the chip's rather conservative architecture not delivering competitive clock-for-clock performance, the bug added to a rather inauspicious compendium of shortcomings.

Nevertheless, the TLB bug can now be crossed off that list. With the B3 stepping it has been banished – at least for all Phenom processors with the '50' suffix in the product number. The X3 triple-core chips will keep the '00' suffix and remain TLB bugged.

But what about clockspeeds? Here the news is less gratifying. Though the new 9850 Black Edition model does raise Phenom's game, the move is from a rather pitiful 2.3GHz to merely mediocre 2.5GHz. To put that into perspective, the slowest model in Intel's latest 45nm quad-core range is clocked at the very same speed. The fastest Intel quad-core CPU now weighs in at 3.2GHz.

Excellent multi-core scaling

As for the 9850's actual performance, it's a tale of two halves. In isolation it delivers a pretty solid experience. The 2.5GHz clockspeed is just enough for decent single-threaded performance. Meanwhile, AMD's integrated memory controller ensures low latency and extremely data high bandwidth to all for cores which makes for excellent multi-core scaling.

Unfortunately, however, the 9850 does not exist in isolation. Currently priced around £155 it must compete with the entry level quad-core chip from Intel's 65nm range, the Q6600. It may only run at 2.4GHz, but the Q6600 still has the measure of the fastest Phenom in most benchmarks. Admittedly, the 9850 does match the Intel opposition in our H.264 video encoding test. But it's squarely beaten in the intensive Crysis CPU gaming gauntlet and Cinebench rendering benchmark, for instance.

Of course, all of that applies to operation at stock frequencies. As a “Black Edition” chip, the Phenom X4 9850 has an unlocked multiplier designed for simple overclocking. However, although AMD appears to have released a little more headroom on this latest quad-core model, the 2.8GHz we achieved remains a modest overclock in the context of what Intel's quad's are typically capable of. Any Core 2 Q6600 you buy today will hit speeds well in excess of 3GHz.

So, AMD's revised Phenom CPU in the form of the new 9850 model is certainly a step in the right direction. But it's simply too incremental to significantly close the gap to Intel. For that we'll have to wait until AMD releases its upcoming 45nm shrink of the Phenom later this year. By then, of course, Intel is expected to be shipping its brand new quad-core chips based on the ominous looking Nehalem architecture. It's not going to get any easier for AMD.