Closer Look at Brisbane
The heading of this section may be misguiding because we don’t have anything special to say about the new Brisbane core. With this core AMD solved the problem of transitioning to a more progressive tech process, so it is in fact a redesigned version of the Windsor, which is the core of all dual-core Socket AM2 processors manufactured on 90nm technology. It’s in the die size, thermal and electric characteristics that we should look for any differences. This is illustrated by the following table:
The Brisbane core incorporates as many transistors as the Windsor core with the same amount of L2 cache memory does. This indicates the lack of any changes on the micro-architecture level on the transition to the thinner tech process. However, the new technology has helped reduce the area of the Athlon 64 X2 die by over 30%.
Unlike its predecessor, the Brisbane exists in one version only, namely with 512KB of L2 cache per core. The version with a larger amount of L2 cache hasn’t yet been redesigned. It’s clear that the reduction of the manufacturing cost is one of the main problems AMD solves with its 65nm core.
This is also indicated by the frequencies of the CPU models based on the new core. AMD has introduced it into midrange rather than into top-end products first.
Well, it’s not exactly correct to say that the Brisbane doesn’t bring anything new at all. There are indeed certain changes, however negligible they may seem. Particularly, AMD’s engineers have implemented support for fractional frequency multipliers that now change with a step of 0.5x instead of 1x as before. As a result, Brisbane-core CPUs may vary by only 100MHz in their default clock rates. This innovation gives some flexibility to the Athlon 64 X2 series due to the enlarged product assortment.