New AMD Phenom II CPUs (Socket AM3) review

After launching its first Phenom II processors last month, AMD has kept up the momentum, today adding five new CPUs to the line-up. The new launches won't change the world - in terms of clock speed they merely slot in behind the 2.8GHz and 3.0GHz parts launched last month. But they are the company's first processors to use its new Socket AM3 platform.

That's not as dramatic a departure as it sounds. The AM3 architecture maintains backward compatibility, so the new chips can be used in existing Socket AM2+ motherboards.

It's not forward-compatible, though, so an older AMD processor won't work with a new AM3 motherboard. To prevent accidents, AM3 uses two fewer pins than its predecessor; AM2 chips don't physically fit in the socket.

AM3 offers just one advantage over previous sockets, but it's an important one: at last, DDR3 support has come to AMD. Though the newer RAM technology offers only small performance benefits over DDR2, adoption is accelerating, and it's projected to become the dominant - and hence cheapest - RAM type by early 2010.

The AM3 architecture can support both DDR2 and DDR3 (though not both at once), giving AMD's platform some timely future-proofing.

Beyond that, it's business as usual, with Core i7-type paradigm shifts conspicuous by their absence.

Our Socket AM3 test board - an Asus M4A79T (see picture) - uses the same 790FX chipset and HyperTransport 3.0 bus as many existing AM2+ motherboards. Only the four DDR3 slots - and the so-subtly changed CPU socket - mark it out as anything new.

The new Phenom IIs

The new processors themselves are low-end Phenom IIs. Three new quad-core parts - the X4 805, X4 810 and X4 910 - are accompanied by the first triple-core Phenoms, the X3 710 and X3 720.

These part numbers reflect a new naming strategy for AMD. 900-series Phenom IIs have 6MB of L3 cache, as with the X4 920 and X4 940 that emerged last month, while 800-series models have only 4MB.

Relative clock speed is, confusingly, reflected in the last two digits of the model number, with five units translating to a speed gap of 100MHz.

Thus, the X4 910 is a 2.6GHz part with 6MB of L3, while the X4 810 and 805 have smaller 4MB L3 caches and clock speeds of 2.6GHz and 2.5GHz respectively.

The two X3 processors released today each have the larger 6MB L3 cache - though as with previous triple-core Phenoms, L2 cache is proportionately shrunken compared to the X4s, at 1.5MB rather than 2MB. Clock speeds are, predictably, 2.8GHz for the X3 720 and 2.6GHz for the X3 710.

Benchmark results

Our benchmarks suggest that the new architecture gives the new chips a real, if not earth-shattering, performance boost.

Last month the 2.8GHz X4 920, tested in a Socket AM2+ board with 2GB of DDR2 RAM achieved an overall benchmark of 1.62 - roughly on a par with Intel's Core 2 Duo E8500. This month the X4 810 running with DDR3 on our AM3 board achieved an identical overall score, despite its smaller L3 cache and slightly lower clock-speed.

The 2.8GHz X3 720, tested in the same board, did even better than the X4 920, achieving an overall score of 1.65 despite being a core down.

It's worth remembering that those scores are made up of a range of individual tests, not all of which derive the same benefit from the switch to AM3 and DDR3. The X4 810 lagged a few per cent behind the X4 920 in our Office, Encoding and Multitasking tests, but made it up in our 2D Graphics test, scoring 1.89 against the 920's 1.81.