AMD Athlon X2 7850 review

High-end Phenom II CPUs have been grabbing the headlines lately, but AMD isn’t neglecting the middle ground either. Over the past few months it’s been quietly moving its AM2-based dual-core Athlon range over to a new core – and a new naming convention. We saw the Athlon X2 7750 in our CPU megatest earlier this year; now we welcome the 7850.

The new model numbers may seem arbitrary, but they fit in with the last generation of Agena-based Phenom processors, such as the Phenom X4 9850. And that makes perfect sense because the new Athlons are based on the same die – but with only two of the four cores active. AMD calls it the Kuma core.

The new Athlons thus emerge with the same basic specifications as the old Phenoms, including 512KB of L2 cache per core, totalling 1MB, and a 2MB L3 cache. The HyperTransport still runs at 1.8GHz, and the chips are still manufactured with a 65nm process.

Reusing the old design may be a canny economic move on AMD’s part, but it means the new Athlons inherit the clock rate limitations of their quad-core progenitors. This top-of-the-range model ships with a comparatively low stock speed of 2.8GHz.

And though it’s a multiplier-unlocked “Black Edition” there’s nowhere near the overclocking headroom offered by AMD’s newer 45nm chips. With stock cooling we managed to up the frequency by just 300MHz before the system became unstable.

Of course, clock speeds can be misleading: it’s real-world performance that matters. In our standard 2D benchmarks, with 2GB of DDR2-522 RAM, the Athlon X2 7850 achieved an overall score of 1.30. Upping the clock speed to 3.1GHz boosted this to 1.41.

Comparing these scores to those achieved by Phenom II systems makes clear that multiple cores do bring a tangible benefit. While the X2 7850 took 8mins 44secs to complete our multi-apps test, a Phenom II X3 720 running at the same frequency cut that time to 6mins 24secs.

But even in our office applications test – not an exercise that relies heavily on multi-threading – the X3 720 shaved 48 seconds off the 7850’s execution time of 6mins 45secs. As we’ve noted before, the advantage of the AM3 microarchitecture over AM2 appears greater than the switch to DDR3 alone would suggest.

But the Athlon X2 7850 isn’t intended for a high-performance role: it’s an unapologetically mid-range processor, with enough power to waltz through everyday tasks. And at fifty quid it’s half the price of the Phenom X3. That makes it a worthy adversary to Intel’s Pentium Dual-Core E5200, which gives similar performance at a similar price but lacks the 7850’s virtualisation support.

Ultimately, though, the X2 7850 is squeezed out by its own little brother, the Athlon X2 7750. That model sells for just £43 exc VAT, and with a stock speed just 100MHz lower the performance gap is negligible – especially since, as with the 7850, it’s multiplier-unlocked.

Prices change, of course, and this latest Athlon could yet carve out a niche for itself. But positioned as it currently is, the X2 7850 fails to excite.