Brisbane-core processors haven’t surprised us with their performance in most applications, even though their L2 cache is slower than that of the Windsor-core models. But besides the default performance, PC enthusiasts may be interested in an overclockability check because a transition to a thinner tech process usually pushes the CPU frequency bar higher. This rule may not apply to the Brisbane, though, as the default clock rate of the new CPUs, declared by AMD, is lower than the frequency of the CPUs on the older 90nm core.
We tried to check this out by overclocking our CPU. We cooled it with an air cooler Zalman CNPS9500 LED. The frequency multiplier of the Brisbane-core Athlon 64 X2 4800+ being limited by the default 12.5x from above, this CPU has to be overclocked in the usual way, by increasing the clock generator frequency. To avoid problems with the other subsystems of the testbed, we reduced the multipliers for the memory and HyperTransport buses (the latter connects the CPU with the mainboard’s SPP).
First, we tried to overclock the CPU at its default voltage of 1.35V. We managed to increase the clock-gen frequency by 15%, to 230MHz.
The system with the Brisbane-core CPU overclocked to 2.87GHz was perfectly stable. This was a good result, but no record in comparison with what you could achieve with Windsor-core CPUs. Then we increased the voltage of our Athlon 64 X2 4800+ to 1.6V. This 18% increase in voltage produced a rather small effect: the maximum stable CPU frequency grew only 4% higher.
Thus, the maximum of frequency we reached without any special cooling methods was 3.0GHz.
In other words, the Brisbane core didn’t provide any advantages over the Windsor in terms of overclockability, either (AMD currently offers 90nm processors for which 3.0GHz is the default frequency). So, you shouldn’t as yet expect any overclocking breakthroughs from AMD’s transition to 65nm tech process.