X-bit labs

Meeting First Socket 939 Processors: AMD Athlon 64 3800+ and Athlon 64 3500+ (page 12)

Category: CPU

by Ilya Gavrichenkov

[ 06/01/2004 | 07:59 AM ]

Overclocking and Temperature

We didn’t have high hopes about the overclockability of the new Socket 939 processors. As I mentioned above, they are all based on the same CG core revision as the Socket 940 Athlon 64 FX-53 we had tested earlier. Without extreme cooling methods, we had only reached a little over 2.6GHz clock rate for that processor. Considering also that the Athlon 64 3800+ is the last CPU model on the 130nm core, I may venture a supposition that Socket 939 Athlon 64 models should speed up to 2.5-2.6GHz and no more, without any special cooling.

Moreover, we should keep in mind the fact that the memory controller of the Athlon 64 is situated in the same chip as the CPU itself, and making a more sophisticated controller inevitably leads to a higher heat dissipation of the processor at large. This means that Socket 939 Athlon 64 processors with a dual-channel memory controller will overclock no better than their Socket 754 counterparts based on the CG core stepping.

Before proceeding to the results we achieved at overclocking our Athlon 64 3800+ and 3500+, we should note the fact that these processors, like the Athlon 64 in the Socket 754 form-factor, have their frequency multiplier locked from above. The new Athlon 64 FX-53 in the Socket 939 form-factor, however, doesn’t have any multiplier lock, as this processor is targeted at computer enthusiasts. Thus, we had to speed up our Athlon 64 3800+ and 3500+ samples by increasing the frequency of the clock generator. Fortunately, the modern chipsets from VIA and NVIDIA (K8T800 Pro and nForce3 250, respectively) employed in mainboards for Socket 939 processors can clock the AGP/PCI busses asynchronously. That is, you may leave these busses at their normal frequencies during overclocking. This way, even if you overclock a CPU with a locked multiplier, you won’t render your peripheral devices non-operational.

We tried to overclock our processors, an Athlon 64 3500+ and 3800+, on an ASUS A8V Deluxe mainboard, using a Thermaltake Silent Boost K8 (A1838) cooler. For better overclocking, we also increased the Vcore by 10%, from the nominal 1.5v to 1.65v.

The maximum frequencies at which the processors kept stable were rather low, as we had expected. Particularly, the Athlon 64 3500+ with 2.2GHz frequency overclocked to 2.55GHz, where we arrived by increasing the FSB frequency to 232MHz. The other processor we tested today, the Athlon 64 3800+, sped up from 2.4GHz to 2.58GHz, the FSB clock rate being 215MHz. Thus, the frequency reserve of Socket 939 processors turned to be somewhat poorer than that of Socket 940 Athlon 64 FX-53 processors. That’s natural, though.

The temperature is an important factor with regard to the reviewed processors, because their integrated memory controller contributes to their heat generation. Of course, the Athlon 64 3500+ and 3800+ models are based on the NewCastle core with only 512KB of L2 cache. Anyway, this fact shouldn’t compensate for the memory controller’s heat, because the transistors of the cache memory don’t add much to the die’s heat dissipation.

To clear up this situation, we measured the temperatures of the reviewed processors under a load and when they were idle. We made our measurements using the thermo diode integrated into the CPU core and reading its data with the hardware monitoring tools of the mainboards.

The Socket 939 Athlon 64 3500+ turns to be colder than its Socket 754 counterpart, the Athlon 64 3400+. It seems strange at first sight, but there’s no mystery after all. The Athlon 64 3400+ we used in our tests was based on the earlier C0 core stepping, which had a lower frequency potential and higher heat dissipation. If we compare the Athlon 64 FX-53 and the Athlon 64 3800+, we may come to the conclusion that the dual-channel memory controller in the Socket 939 CPU generates a lot of heat.

By the way, all Socket 939 processors, including Athlon 64 3800+ and 3500+, and also the Athlon 64 FX-53, feature Cool’n’Quiet technology for reducing the temperature and heat dissipation under small workloads.