Phenom II X2 vs. Athlon II X2 - A Question of Cache

A Question of Cache

A Question of Cache

AMD's dual-core Phenom II X2 555 'Black Edition' has kept us occupied for a while, what with its ability to be unlocked by the proper motherboard/BIOS to a full Phenom II X4 processor. Although we did not succeed in our initial attempts, we subsequently managed to do so using an MSI 790FX-GD70 motherboard. It was simply a matter of changing a BIOS setting to get it unlocked, which CPU-Z then identified as a Phenom II X4 B55. This experience was documented in the latest April issue of HWM, but that's not all we had in mind with the Phenom II X2 555 BE. 

AMD also has another dual-core series, the Athlon II X2, which is based on a different core and is a true dual-core. This means that unlike the Phenom II X2 555 BE, which has four cores at its heart, there are no extra cores to enable on the Athlon II X2. AMD has released a newer model in the Athlon II series, the X2 255 along with the Phenom II X2 555 BE, but what intrigued us is the similarity between the two. Both are almost at the same frequency, the Athlon II X2 255 runs at 3.1GHz and the Phenom II X2 555 at 3.2GHz. The main difference lies in the amount and hierarchy of its cache.

As most techies know, CPU cache is basically the amount of on-die memory on the processor. It's the closest and fastest source of memory for the CPU and there's drastically less penalty in accessing the cache than the slower system memory (RAM). On modern x86 processors, there's usually a cache hierarchy, where L1 cache has lower latency than L2 and so on.

The Phenom II X2 has a substantial amount of  L3 cache (a total of 6MB) while the Athlon II X2 has no L3 cache. It does have 2MB of L2 cache to compensate, compared to 1MB on the Phenom II X2. Both have the same amount of L1. This difference is what we're looking at today, since besides the cache, the architecture for both processors is similar. Exacly how beneficial is the extra cache and should you opt for an Athlon II or Phenom II series? Before we proceed to our test performance results to find out, here's how the two AMD dual-core processor series stack up:

Athlon II X2 vs Phenom II X2
Processor Models Clock Speeds
L2 Cache L3 Cache Max TDP (W)
Retail Price (US$)
Athlon II X2 240, 245, 250, 255 2.8 - 3.1GHz 2MB Nil 65 53 - 65
Phenom II X2 545, 550, 555 BE 3.0 - 3.2GHz 1MB 6MB 80 88 - 101


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