Related Articles

Overclocking

As you saw from the results presented in the charts, we were quite successful in overclocking the 840 D. Our final stable overclocked speed was 4.04GHz, a massive jump from the stock 3.2GHz.

What did we do?

- used a watercooler to try and keep the processor temperature under control

- raised the processor voltage a bit, to 1.425Vcore from the standard 1.375V

- raised the DDR2 voltage .1V

- left the memory timing at 5-4-4-9

- changed the FSB speed to 1160MHz (4x290MHz, from 800MHz - 4x200MHz)

Without the water cooler, the highest processor speed we could reach with any reliability was approximately 3.8GHz - the water cooling got us up stably to 4.04GHz with both cores being 100% occupied!

Conclusion

Yes, Virginia, dual cores on the Intel does help.

The Intel 840 D fared quite well in dual core tests, especially where the applications did not need to saturate the FSB with memory reads/writes; for compute bound applications you can get nearly twice the processing power that you could get from a single core.

Things don't quite work as well when one or both of the cores has to make a lot of memory requests; then they end up fighting for FSB bandwidth. The problem is clearly not memory bandwidth - with dual DDR2 memory channels we could get theoretically all the way up to 16GB/sec memory bandwidth (ignoring latencies, in the real world 14GB would be a more likely maximum) - however the P4 FSB limits how much of that potential memory can reach the processor to less than 6.4GB/sec at 800MHz FSB, or less than 8.5GB/sec at 1066MHz FSB. Granted, some of the potential memory bandwidth could be used for DMA by IO or graphics devices, but the processor can't get to it.

Intel of course realizes this limitation, and is moving to a 1066MHz FSB allowing for up to 8.5GB/sec bandwidth; in the lab we have already successfully ran some Intel processors with an FSB speed approaching 1GHz - later Intel is likely to move to a 1333MHz FSB. Further in the future, Intel will be moving to a more HyperTransport like interconnect scheme, which was initially going to appear on the Itanium processors as the "CSI" interconnect.

The 840 overclocked VERY well with water cooling, but our lab got appreciably warmer when we were stress testing it by loading both cores to 100% utilization. The jump from the official 3.2GHz to the maximum stable 4.04GHz we achieved is nothing to sneeze at, and proves to us that Intel could release 4GHz processors any time it chose to, assuming it would be willing to accept very high thermal dissapation and power consumption.

If your applications could benefit from a second core - or you run several applications at once - dual cores will help; however if your applications saturate the FSB, you will not realize anywhere near as much benefit as you can when the applications are not processor bound and don't spend a lot of their time fighting for memory bandwidth. The end result is that for those of you who need a dual core, the 840-D, with its good overclocking overhead and very decent results might serve your needs nicely.