AMD Athlon II X4 635
The second AMD processor participating in our today’s study, Athlon II X4 635, belongs to the same Athlon II family, but in reality is dramatically different from the X2 models. This CPU is based on a different semiconductor die aka Propus that is a monolithic quad-core die manufactured with 45 nm process. From the user prospective Athlon II X4 635 processor is especially interesting because it is one of the least expensive quad-core CPUs available in the today’s market. As for the specs, Athlon II X4 635 is designed for Socket AM3 platform and works at 2.9 GHz clock frequency. I have to point out that unlike Phenom II processors, Athlon II X4 has no L3 cache, and provides 512 KB of L2 cache per core.
The nominal Vcore of our Athlon II X4 635 was 1.4 V, and the voltage of the North Bridge integrated into the processor was set at 1.175 V. In other words, Athlon II X4 635 works with the same voltages as its dual-core brother. Nevertheless, twice the number of computational cores did affect the calculated TDP of this processor. For Athlon II X4 635 it is 95 W. As far as the practical values are concerned, our system equipped with this processor working at 2.9 GHz clock frequency consumed 146 W under heavy load, which is 35 W more than the same platform equipped with a dual-core Athlon II X2 255 would consume. The practical power consumption along the processor power line was 96 W.
I have to say that Propus processor family should be considered the least overclocking-friendly contemporary CPUs. While most widely available processors can hit frequencies up to 4 GHz, the tested Athlon II X4 635 could only go as high as 3.5 GHz. Moreover, to ensure that it remained stable at this frequency we had to increase its core voltage by 0.1 V. The maximum frequency we could get this CPU to work at without adjusting the core voltage was 3.4 GHz. Just like in the previous case, we overclocked by changing the clock generator frequency, because Athlon II X4 635 has a locked clock frequency multiplier.
Like in the previous case, we took a number of readings to check out the type of dependence between the power consumption and frequency. The table below described the key knots and major settings for our testbed:
All other voltages, not mentioned in the table above remained at their defaults.
The graph below shows total power consumption under maximum workload depending on the processor frequency.
This is not a new picture for us. While the CPU Vcore remains unchanged, power consumption increases strictly linearly and with a pretty low coefficient. However, once we slightly increase the CPU core voltage, we immediately see a dramatic increase in power consumption on the graph. For example, in our case the increase in CPU Vcore from 1.4 V to 1.5 V produces 25 W higher power consumption reading, although all other system voltages do not change and the CPU clock speed gets only 100 MHz higher.
The second graph here shows the changes in currents feeding the CPU and the mainboard during overclocking:
I would like to draw your attention primarily to the curve showing increase in the CPU current. At least, the change in processor frequency barely affects the currents fed to the mainboard through a 24-pin power connector, just like in the previous case. As for the processor power consumption, when we overclocked our Athlon II X4 635 from 2.9 to 3.5 GHz, it changed from 96 W to 137 W, and the lion’s share of this increase occurred in the interval between 3.4 and 3.5 GHz, when we had to increase the core voltage.