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AMD A8-3870K Overclocking

The specifications of the AMD A8-3870K didn’t surprise us in any way. It is a totally common quad-core Llano processor. However, its peculiarity is in a different aspect and is indicated by the “K” suffix in the model name and the fact that A8-3870K belongs to the “Black Edition” series. In other words, this processor is an overclocking-friendly product with unlocked multipliers responsible for all operational frequencies.

This is a serious advantage that A8-3870K has over its predecessors, because overclocking Socket FM1 processors by raising the clock generator frequency is usually very complicated. The problems arise because the same base clock frequency is used for the computational and graphics core frequencies as well as for clocking the controllers integrated into the chipset. As a result, overclocking by raising the base clock often causes failure of SATA devices in AHCI mode, as well as D-Sub and HDMI outs on the mainboards. A8-3870K doesn’t have any of the above described problems, because it can be overclocked without adjusting the base clock frequency.

I would like to remind you that Llano processors have three major frequencies, which directly affect the performance and which make sense to adjust during overclocking:

  • Clock frequency of the computational CPU cores;
  • Graphics core frequency;
  • DDR3 memory frequency.

A8-3870K allows you to easily adjust any two of the three frequencies. The computational core frequency is adjusted with the unlocked processor clock multiplier, which can be changed in 1x increments from 8x to 47x. In other words, keeping in mind that Socket FM1 systems work with 100 MHz BCLK, A8-3870K may theoretically work with any clock frequency with 100 MHz increments.

Our today’s hero allows adjusting the graphics core frequency as well. However, in this case the algorithm is more complex: this frequency is created by dividing the resulting processor clock by its own multiplier, which can be adjusted with 0.25 increments. Therefore, the discontinuity of the GPU frequency is variable and depends directly on the processor overclocking.

The memory frequency in A8-3870K is determined by a special multiplier, which can be adjusted within very limited intervals. Like all other Llano, A8-3870K only supports DDR3-1067, DDR3-1333, DDR3-1600 and DDR3-1867 SDRAM. It means that the memory controller has only four multipliers available for shaping up the memory frequency: 10.66x, 13.33x, 16.0x and 18.67x. In other words, even for the A8-3870K processor, which belongs to the Black Edition series, the highest memory mode attainable without changing the BCLK frequency will be DDR3-1867 SDRAM. For more advanced memory overclocking, you will need to increase the BCLK frequency beyond its nominal value.

Everything I have just said is summed up on the following illustration:

In practical terms, all this means that Llano processors with locked clock frequency multipliers could be successfully overclocked to about 3.5 GHz with symmetrical increase in the integrated graphics core frequency to 870 MHz. However, since this overclocking was performed by raising the clock generator frequency to 140-150 MHz, some sacrifices had to be made, such as switching the SATA drives into a less efficient IDE mode and use DVI monitors.

With A8-3870K Black Edition no one promises any new overclocking records. However, when you overclock this processor with multipliers, all system components continue working in nominal modes, so there is no need to compromise. Even AMD states that A8-3870K processors should easily hit 3.5-3.8 GHz on the computational cores and up to 800-960 MHz on the graphics core with just air-cooling alone. During our experiments, we easily reached the indicated frequency intervals.

Our A8-3870K sample under NZXT Havik 140 cooler remained perfectly stable at 3.6 GHz, and its Radeon HD 6550D graphics core easily overclocked to 960 MHz. We needed to increase three major voltages to achieve this result. The processor Vcore was raised to 1.525 V, the nominal voltage of the chipset North Bridge was increased by 0.175 V and the integrated GPU voltage was set at 1.25 V. Since we didn’t change the BCLK frequency, the memory worked in the maximum available operational mode – as DDR3-1866.

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