Despite its Phenom II branding, this series of processors is AMD's third attempt to get Phenom right. The basic AMD64 architecture remains unchanged, although AMD has made several unspecified improvements to the core execution engine.
The single biggest improvement to Phenom II is the change from 65nm to 45nm transistors. As anybody who has followed semiconductor manufacturing process development can tell you, smaller transistors consume and waste less power than larger transistors. High power consumption was the Achilles heel of the original Phenoms - it limited the frequency at which AMD could clock them, made them run extremely hot and severely limited overclocking. Due to their smaller transistors, Phenom IIs run considerably cooler than the original Phenoms, despite running at higher frequencies.
The smaller manufacturing process also provides more room in the die for additional cache. Each of the four cores has 128KB of Level 1 cache and 512KB of Level 2 cache, but the Level 3 cache shared by all the cores has been at least doubled, and in some models, trebled. AMD estimates the increase in Level 3 cache should yield on average an additional 6 per cent extra performance over a Phenom X4 running at the same frequency.
At the time of writing, AMD had launched three Phenom II X4s. The 940 Black Edition is clocked at 3GHz, and has 6MB of Level 3 cache and the same Socket AM2+ packaging as the Phenom X3 and X4. As a Black Edition chip has an unlocked CPU multiplier, the CPU can be easily overclocked without having to worry about adjusting the frequency of the HTT or RAM, or HTT multiplier. The 920 Black Edition has the same cache configuration and Socket AM2+ packaging, but its CPU multiplier is locked and it's clocked at 2.8GHz. Both of these models support standard DDR2 RAM.
The 920 is priced very similarly to the Core 2 Duo E8500, Core 2 Quad Q6600 and Q8300. Although the 920 is very competitive at heavily multithreaded tasks such as video encoding and 3D rendering, the higher frequency of the E8500 makes it much faster in other applications and games. We managed to overclock the 920 from 2.8GHz to 3.5GHz by raising its vcore to 1.425V, but even then, on average, it was slightly slower than the similarly priced Intel CPUs.
The 940 Black Edition is a close price match to the Core 2 Quad Q9300, and faster in most applications and games. The 940 Black Edition further improved its performance lead when overclocked; thanks to the unlocked CPU multiplier, we could boost its frequency from 3GHz to 3.6GHz with a vcore of 1.45V. Even when overclocked to 3.3GHz, the Q9300 failed to close the performance gap with the overclocked 940 Black Edition. However, the Q9300 isn't a very competitive Core 2 Quad, and when compared to the Core 2 Duo E8500, the 940 Black Edition, even when overclocked, comes off significantly worse.
AMD has recently added a third chip to the Phenom II X4 series. The 810 is clocked at just 2.6GHz and has a smaller 4MB of Level 3 cache, but its integrated memory controller can address both DDR2 and DDR3 memory. For this reason, it uses the new Socket AM3 package, which although officially pin-compatible with Socket AM2+, we couldn't get to work in any of the Socket AM2+ motherboards in our lab. As a result, we had to test the 810 in a Socket AM3 motherboard with DDR3 memory.
Despite the higher bandwidth of DDR3 memory, the lower frequency of the 810 means that it lags behind the 920 with its DDR2 memory. However, the 810 is £11 cheaper than the 920, bringing it more into line with the Core 2 Duo E8400, although the latter is significantly faster.
If motherboard manufacturers enable Socket AM3 CPU support in their Socket AM2+ motherboards the 810 will become a more interesting proposition, but as it stands, it would be daft to partner a cheap mid-priced CPU with an expensive motherboard and RAM.
Ultimately, while the Phenom II X4 series is a massive improvement over Phenom X4 - it provides extra performance, runs cooler, draws less power and overclocks further - it's only worth buying if you already have a Socket AM2+ motherboard. For everyone else, a similarly priced Core 2 Duo or Core 2 Quad is a better option.
Author: James Gorbold & Antony Leather
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