X-bit labs

Windows XP Professional x64 Edition Preview: AMD64 and Intel Extended Memory 64 Technology (page 9)

Category: CPU

by Ilya Gavrichenkov

[ 02/08/2005 | 02:16 PM ]

64-Bit Applications Performance

Despite the software compatibility of 64-bit extensions implemented in CPUs from Intel and AMD, they have completely different implementation in the hardware. This is exactly the reason why applications ported for 64-bit operating systems can demonstrate different performance dynamics on CPUs with AMD64 and EM64T. In order to investigate in detail the performance of Athlon 64 and Pentium 4 processors in the 64-bit mode of Windows XP Professional x64 Edition, we collected a few benchmarks, which already exist in 32-bit and 64-bit versions.

A widely spread test application containing both: 32-bit and 64-bit code is SiSoft Sandra 2005 SP1. Depending on the version of the operating system, this program runs either on the 32-bit or on the 64-bit core. As a result, we can use the small synthetic benchmarks of SiSoft Sandra 2005 SP1 to compare the performance of Athlon 64 and Pentium 4 processors in 64-bit modes against their performance in 32-bit modes.

The obtained results are very curious. While Pentium 4 processor with EM64T support benefits from the shift to 64-bit mode in almost every benchmark, the competitor from AMD is very often getting fewer points in 64-bit OS compared with its results in 32-bit operating system. However, I would like to assure you right away that this result is not indicating any overall performance drop of Athlon 64 based systems in 64-bit work mode. The problem actually lies with the SiSoft Sandra 2005 SP1 benchmark, which is better optimized for Intel EM64T architecture. Our analysis shows that SiSoftware uses an Intel compiler to form the execution code for its benchmarks. Moreover, 32-bit and 64-bit benchmark versions use different algorithms based on unequa instructions sets. Therefore, you shouldn’t base your verdict on the results of only this particular benchmark.