Articles: CPU

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Also we will run one more computational benchmark measuring how fast the Mandelbrot set can be built. You can read more about this benchmark here.

We see the same situation as the one we have just discussed about PovRay 3.6. The 64-bit version of this benchmark works slower on Pentium 4 processor with EM64T support than the 32-bit version. In case of Athlon 64 processor, the situation changes to the opposite: the use 64-bit extensions improves the computational performance by the good 29%.

This behavior of the Pentium 4 processor with EM64T technology is pretty understandable. The thing is that Athlon 64 processors were initially developed as 64-bit solutions. It means that Athlon 64 simply doesn’t use some of its potential power when working with 32-bit code. As a result, Athlon 64 processor processes instructions almost equally fast for 32-bit and 64-bit code. However, since there are additional registers and also wider registers, which can be used, the performance can be significantly improved in some cases.

It is a different story with Pentium 4 processors supporting EM64T technology. When Intel engineers developed NetBurst architecture, they didn’t think about the potential advancement of this architecture for 64-bit modes. That is why they had to slightly revise the NetBurst architecture for Prescott core when they decided to introduce EM64T support. By the way, this is exactly why Prescott based Pentium 4 processors sometimes turn out slower than their Northwood based counterparts in 32-bit applications. But this is not all yet. Some instructions, such as integer multiplication or shift are performed much slower in 64-bit mode than their 32-bit analogs because of the NetBurst architectural peculiarities. Therefore, porting programs with integer arithmetic for EM64T may sometimes cause their slowing down, even though there are more general-purpose registers involved and the register width is higher.

Mandelbrot benchmark and PovRay 3.6 are exactly the tasks of the kind: both these applications work actively with integers and use multiplication a lot. That is why the results you saw above are absolutely natural.

Unfortunately, there are no gaming applications yet which could take advantage of 64-bit extensions. The first game to use the 64-bit code will most likely be the ported FarCry, although it is still unavailable. Despite this fact we managed to find some 64-bit 3D applications for our test session this time. Take for instance BobbyDancer from NVIDIA. With this 3D demo we could also test the performance of 64-bit AMD64 and EM64T extensions from AMD and Intel.

According to the obtained results, 3D applications can also benefit quite noticeably from 64-bit extensions. And in this particular case the performance gain is equal for Pentium 4 with EM64T and Athlon 64. It allows us to hope that real 64-bit gaming applications will also run faster in Windows XP Professional x64 Edition.

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