Conclusion

As we have expected, nothing serious has happened. CPUs with Intel Core microarchitecture and EM64T technology work normally in 64-bit modes. No dramatic performance drop has been detected in most benchmarks.

Of course, there are a few applications, when Core 2 Duo work slower in their 64-bit versions than it would in their 32-bit ones. Among them are Windows Media Encoder 9 or 7-zip archiving tool, for instance. However, since the other testing participants have also lost some of their performance in these tasks, the problem is most likely to be not in the microarchitecture. EM64T technology of Core 2 Duo processors has a positive effect on the performance in the majority of applications.

The diagram shows the performance increase (in percents)
for CPUs with Intel Core and AMD K8 microarchitecture
when we switch from 32-bit to 64-bit applications.

At the same time I would like to point out that it looks like Athlon 64 processors ensure higher performance increase when switching to 64-bit work mode. The average performance improvement we have seen from Athlon 64 FX-62 equaled 16%, while Core 2 Extreme X6800 demonstrated only 10% average performance boost. This way, there is a certain difference: AMD K8 turns out 6% mode efficient in 64-bit mode than Intel Core. However, this difference cannot compensate for the 20% performance advantage of the Intel Core 2 Duo over the Athlon 64 X2 working at the same clock speed, which we have pointed out in our previous articles. Therefore, we will not change our conclusions about the performance of the new Intel processors even keeping in mind the upcoming launch of 64-bit Windows Vista OS family.