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Overclocking

We have repeatedly compared the Socket 939 Sempron with the Athlon 64 in this review. Our Socket 939 Sempron 3000+, based on a Palermo core, has much in common with the Athlon 64 3000+ on the E3 stepping Venice core. And we would really want the Socket 939 Sempron 3000+ to have the same consumer qualities as Venice-core Athlon 64 CPUs, particularly in terms of overclockability.

Athlon 64 CPUs with an analogous core of the E3 stepping have a good overclocking potential in general, so overclockers may be interested in appropriate tests of the reviewed Sempron. So, how does it do at overclocking? To answer this question we assembled this testbed:

  • Sempron 3000+ CPU (Socket 939, 1.8GHz, 128KB L2 cache, Palermo revision E3)
  • Zalman CNPS9500 LED cooler
  • DFI NF4 Ultra-D mainboard (Socket 939, NVIDIA nForce4 Ultra)
  • Corsair CMX512-3200XL, 2 x 512MB, DDR400 SDRAM, 2-2-2-5
  • PowerColor RADEON X800 XT (PCI-Express x16)
  • Maxtor MaXLine III 250GB (SATA150)

We mounted a powerful CPU cooler to get better results, but this measure proved to be superfluous. Having low power consumption and heat dissipation, the reviewed Sempron 3000+ for Socket 939 was not too hot even when we increased its voltage and used a standard aluminum cooler. So, you don’t have to spend your money for a top-end cooler if you’ve got a Sempron on an E revision core. This will bring just a minor overclocking gain, if any. The Sempron 3000+ has a default frequency of 1.8GHz; its frequency multiplier is 9x. Since this CPU supports Cool’n’Quiet technology, its multiplier can be decreased, but cannot be increased. So, we will have to raise the clock-gen frequency very high, if our CPU has a good overclocking potential. And it means we have to use a high-quality mainboard.

Frankly speaking, our overclocking experience with Palermo-core Socket 754 Semprons has been rather ambiguous. There are samples that can work at frequencies up to 2.8GHz without any special cooling, but there are also samples that find it difficult to start up even at 2.4GHz. AMD’s policy with respect to Semprons obviously implies using in them cores that do not suit for more expensive CPUs, for example for Athlon 64. But it seems that sometimes these “defective” cores are so few that AMD has to use “normal” cores (i.e. with a high frequency potential) for the Sempron, too. As a consequence, overclocking a Sempron is like a lottery the outcome of which you can hardly predict. That’s why we shouldn’t extrapolate the overclocking performance of one Sempron sample to another. The result may differ dramatically in each particular case.

As for our sample of the Socket 939 Sempron 3000+, we first checked it at its default voltage. Without losing stability we increased the frequency of the clock generator from 200 to 255MHz. The resulting CPU frequency was 2295MHz. This was not a satisfactory result, so we continued our experiments at a higher CPU voltage.

Having set it at 1.55V, we found the system to behave much better. For example, the OS could boot up at clock-gen frequencies up to 283MHz, i.e. up to 2547MHz CPU clock rate. The system was far from stable at that, however, so we began to reduce the clock-gen frequency until the computer could pass some basic tests (S&M, SuperPi and 3DMark 2001SE). Unfortunately, we had to go down for quite long – the system only became absolutely stable at 270MHz clock-gen frequency. So, we managed to overclock the CPU to 2.43GHz at 1.55V voltage.

This is not impressive, either, since the CPU frequency grew up by 35% only. The resulting frequency was just a little higher than the default frequency of the Athlon 64 3800+ processor that is based on an analogous core of the same E3 stepping. We must have been not very lucky with the sample of the processor.

Yet you should not think it was just a rare accident. We took two more Socket 939 Sempron 3000+ samples from the same batch and found their frequency potential to be much alike.

 
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