Windows XP Professional x64 Edition Preview: AMD64 and Intel Extended Memory 64 Technology

We would like to offer you a detailed preview of the Release candidate 1 of the new Windows XP Professional x64 Edition operating system. In this article we will compare the performance of the AMD and Intel processors in 32-bit and 64-bit applications.

by Ilya Gavrichenkov
02/08/2005 | 02:16 PM

The operating systems from Microsoft supporting 64bit extensions of the x86 architecture are still one of the most acute topics for discussion out there. The thing is that there are quite a few processors in the market, which support x86-64, although there are still no mass operating systems fort this architecture. At present the owners of 64-bit AMD Athlon 64 FX and AMD Athlon 64 processors have either to out up with the fact that their CPU doesn’t use its given potential power to the full extent when working under 32-bit operating systems, or to got for Linux systems, which are  considerably less popular compared to Windows.


The need for 64-bit Windows-type of systems compatible with the x86-64 bit architecture gets even more and more vital since the Intel’s new processors are also going to acquire 64bit extensions support in the nearest future. The upcoming Intel Pentium 4 XE and Intel Pentium 4 6XX processors due later this month, will also support 64-bit extensions of the x86 architecture, just like their competitors from AMD. Also, they will introduce compatibility with x86-64 architecture in their budget Celeron D processors in the nearest future.

After a few unplanned delays, Microsoft is going to finally launch their Windows operating systems for CPUs with x86-64 architecture in the first half of 2005. The first system from this family, Windows XP Professional x64 Edition, is expected to be officially announced during CeBIT in Germany, which traditionally takes place in early spring. In the meanwhile, in the beginning of this year, Microsoft provided the Release candidate 1 of this operating system, which they allow using for introductory purposes. So, our today’s article is going to be devoted to the features and peculiarities of the upcoming Windows XP Professional x64 Edition version 1289, which is none other but this particular RC1.

Advantages of Windows XP Professional x64 Edition

It is evident that the announcement of Windows XP Professional x64 Edition may turn out a significant stimulus for the software market as well as for the processor market, because the support of x86-64 by the operating systems will certainly offer the users a list of indisputable advantages.

Microsoft Corporation singles out five major reasons why Windows XP Professional x64 Edition will be more preferable than any of the currently widely spread 32-bit Windows-type operating systems.

First of all, Windows XP Professional x64 Edition is a new operating system, which can work with 64-bit application, which improves notably the performance and data processing efficiency. This advanced efficiency is achieved due to the fact that 64-bit applications can work with larger general purpose registers, and the number of these registers has become twice as big, compared with what the classical x86 architecture provides.

Secondly, Windows XP Professional x64 Edition supports much larger memory capacities. Thus, the maximum amount of physical memory supported by this new operating system is 32GB. As far as the virtual memory is concerned, the new operating system can support up to 16 terabytes of virtual memory. This way, the applications for Windows XP Professional x64 Edition are capable of processing much larger packs of data in the RAM. As you probably know, the 32-bit Windows versions cannot address more than 4GB of memory and do not allow allocating more than 2GB of memory for a single process. Windows XP Professional x64 Edition will completely eliminate these limitations.

Thirdly, one of the indisputable advantages of Windows XP Professional x64 Edition is the ability of this system to work not only with the 64-bit applications, but also with the traditional 32-bit applications without any functionality limitations or performance drops. This is possible due to a special x86 Windows on Windows 64 (WOW64) emulator built into the OS.

Also, among the advantages of Windows XP Professional x64 Edition Microsoft mentions the support of up to 2 single- or dual-core x86-64 processors and a corresponding programming model the software developers are already familiar with.

It is important to understand that all major advantages of Windows XP Professional x64 Edition are not that much the achievements of the Microsoft software developers, but are determined by the hardware innovations implemented in the new AMD and Intel CPUs supporting 64-bit extensions. Among these remarkable innovations I should definitely mention the new processor mode (Long 64-bit Mode), providing the support of 16 64-bit registers and linear 64-bit addressing. The backward compatibility with 32-bit applications is ensured by a special Compatibility Mode. These particular processor work modes are exactly the work modes the new Windows XP Professional x64 Edition operating system can use efficiently.

Although 64-bit extensions implemented in AMD processors are called AMD64, and in Intel processors are called EM64T (Extended Memory 64 Technology), they are compatible on the software level. In other words, Windows XP Professional x64 Edition can work on Athlon 64 processors supporting AMD64, as well as on Intel Pentium 4 processors supporting EM64T. Note that all applications developed for this OS should have no trouble working on either platform.

Windows XP Professional x64 Edition v.1289

We have already discussed the beta versions of Windows XP Professional x64 Edition operating system on our site. In particular, we received from Microsoft a number of OS versions for our testing needs. Since the end of 2003 we have got the following beta-versions: 1039, 1069 and 1218. Each newer version improved certain flaws and eliminated certain bugs of the predecessor, and offered better compatibility with the new processors supporting 64-bit extensions. However, all these versions were still very far from the way the end product was supposed to look like. The current revision 1289 has been assigned the status of Release Candidate 1, which indicates that it is close to the final OS version. This appeared exactly the reason why we decided to take another close look at Windows XP Professional x64 Edition and to find out how the owners of CPUs with 64-bit extensions can benefit from the new operating system by Microsoft, once it is released.

Right now RC1 of the new operating system is available for free download on Microsoft’s web-site. If you register here, you can get access to a 360-day trial version of Windows XP Professional x64 Edition RC1. if you decide to install this OS, you have to make sure that your computer complies with the minimum system requirements, such as 256MB of memory, 1.5GB of disk space, a VGA card supporting at least 800x600 resolution, CD or DVD ROM drive, a mouse and keyboard. As far as the CPU is concerned, Windows XP Professional x64 Edition is compatible with AMD Athlon 64, AMD Opteron, Intel Xeon with Intel EM64T support and Intel Pentium 4 with Intel EM64T support. Note that Windows XP Professional x64 Edition will not support 64-bit Intel Itanium processors with IA64 architecture. For these particular CPUs Microsoft offers another 64-bit operating system with a similar sounding name: Windows XP 64-Bit Edition.

The installation of Windows XP Professional x64 Edition goes just like the installation of the regular Windows XP, and shouldn’t cause any problems. Once the OS is installed, the user has to find the 64-bit drivers for all system devices. The 32-bit drivers used in traditional Windows XP versions do not work for the new operating system.

We have already mentioned in our earlier articles that 64-bit drivers for the new OS are currently offered only by a limited number of hardware developers. Luckily the situation got much better since then. You can check out a pretty long list of devices with the available 64-bit driver support here. Well, when you look at this list, you get the impression that almost all the most widely spread devices have already acquired 64-bit drivers. However, I would recommend that you check out this list for your system before you start installing Windows XP Professional x64 Edition.

Windows XP Professional x64 Edition operating system looks very similar to the regular Windows XP Professional with the integrated Service Pack 2. The RC1 we had at our disposal this time already featured Security Center with the enhanced Windows Firewall.

Moreover, Windows XP Professional x64 Edition also supports NX-bit to the full extent. Just like in Windows XP Professional SP2, NX-bit check can be disabled for individual applications.

The situation with available applications is a little bit more curious. As for the native 64-bit programs developed specifically for Windows XP Professional x64 Edition, they are still not that numerous. Besides those few 64-bit applications included into the package, such as 64-bit version of the Internet Explorer, there are really few other programs you can now get for your Windows XP Professional x64 Edition. Among the Windows software developed by other companies, which has already been ported for the x86-64 architecture, I would like to point out Mozilla Firefox, Avast Antivirus 4.5 and McAfee Enterprise 8.0i antivirus software, and a number of small utilities for system and hardware configuring. Moreover, it is great that they also have 64-bit beta version of Microsoft .Net Framework.

Now I would like to say a few words about the work of 64-bit browser versions. The thing is that Internet surfing with the 64-bit browsers appears somewhat complicated because there are no 64-bit versions for many popular plug-ins. Today we don’t know anything about the new 64-bit plug-ins other than Macromedia Flash, Shockwave and Java VM. As a result, you will have to surf around many web-sites using ActiveX components with the 32-bit browser versions only. For this particular purpose they also include a 32-bit Internet Explorer version into the OS package as well. The funny observation of ours: among the sites, which do not work with 64-bit browsers we also discovered Windows Update site :)

However, do not be too frustrated about the absence of native 64-bit applications for Windows XP Professional x64 Edition. The big advantage of this OS is the availability of a special x86 Windows on Windows 64 (WOW64) emulator, which allows using the regular 32-bit software. Almost all 32-bit applications will work in Windows XP Professional x64 Edition without any problems. Although there are a few exceptions here. For instance, Windows XP Professional x64 Edition will not support some 32-bit versions of antivirus software and Starforce copy protection system, which will prevent you from running some games in the new OS too. This is also true for the old 16-bit programs from the times of good old Windows 3.XX: these applications will not work in Windows XP Professional x64 Edition at all.

Testbed and Methods

At this moment we have both in our labs: Athlon 64 processors supporting AMD64 as well as Pentium 4 processors supporting EM64T technology. Therefore, it was really exciting to see how efficient and fast the new Windows XP Professional x64 Edition operating system could be on systems built around different CPUs. First of all we decided to pay attention to the fact if the use of 32-bit applications in the 64-bit OS causes any performance slow-down. Secondly, we tried to estimate how big is the benefit from porting 32-bit applications for the 64-bit architecture. And thirdly, we compared the efficiency of the 64-bit extensions implemented in the CPUs from two eternal rivals: AMD and Intel.

Our test platforms were configured as follows:

The installation of Windows XP Professional x64 Edition was successfully completed on both systems without any problems.

All the drivers needed for our test systems, including those for the NVIDIA nForce4 chipset and the graphics card, are available on the manufacturers’ web-sites. That is why we didn’t have any problems during the system setup. Therefore, let me go directly to the benchmarks results and answers to the questions set above.

32-Bit Applications Performance

In the first part of our test session we decided to test the performance of our systems in 32-bit applications run in the WOW64 emulator of our Windows XP Professional x64 Edition and compare it with the performance we get in the same applications run under Windows XP Professional SP2. For this purpose we ran the same 32-bit applications in the new OS and in the regular Windows XP Professional SP2. We performed this testing experiment for both: AMD Athlon 64 based system and Intel Pentium 4 based system, which allowed us to evaluate the efficiency of the CPUs from different manufacturers for work with WOW64 emulator.

As we see, while we do not get to 3D graphics, i.e. until we involve the graphics drivers, Windows XP Professional x64 Edition performs very impressive. Athlon 64 as well as Pentium 4 work with 32-bit applications almost as fast as in the 32-bit Windows XP Professional SP2. In other words, the use of 64-bit operating system with the CPUs based on x86-64 architecture doesn’t have any negative influence on the performance in old 32-bit applications. Windows XP Professional x64 Edition switches the CPUs correctly into the compatibility mode, so that the 32-bit programs see CPUs with 64-bit extensions as if they had no 64-bit support.

Now let’s see how the situation will look in gaming applications involving 3D power of the graphics subsystem. The earlier beta-versions of Windows XP Professional x64 Edition demonstrated very low performance in this case. At that time we considered raw drivers to be responsible for this low performance level. Now that quite a lot of time has already passed and RC1 operating system appeared, these problems should no longer be there. Let’s find out if this supposition is true:

The performance of 64-bit processors in 32-bit games run from the 64-bit version of the system OS proved to be quite acceptable. No doubt the 64-bit versions of the graphics card drivers have been significantly improved since the last time we worked with them. So, now the performance of our systems in 3D applications in Windows XP Professional x64 Edition is comparable with what we see in the same tasks in a regular 32-bit OS.

However, I would still like to stress that the performance of the tested Athlon 64 and Pentium 4 processors in the 64-bit Windows version is somewhat lower than the results obtained in 32-bit operating system. Although, this performance difference doesn’t exceed 5% that is why I decided to disregard it for now.

Summing up the obtained results let me offer you a final diagram showing the performance changes when we switch from Windows XP Professional SP2 to Windows XP Professional x64 Edition in systems based on Athlon 64 with AMD64 support and Pentium 4 with Intel Extended Memory 64 Technology support.

This graph illustrates very clearly that the performance of 32-bit applications in Windows XP Professional x64 Edition is hardly dependent on the type of 64-bit extensions implemented in the CPU. Both: Intel Pentium 4 with EM64T technology and AMD Athlon 64 with AMD64 technology are almost equally efficient when working with 32-bit applications in Windows XP Professional x64 Edition. Note that this efficiency is relatively high in both cases, which slows down the 32-bit applications run in 64bit operating system by maximum 5% in the worst case compared with the performance of the same applications in a 32-bit OS.

When we tested 32-bit applications in Windows XP Professional x64 Edition we obtained pretty logical results. However, let’s now check the performance of Athlon 64 and Pentium 4 processors in native 64-bit programs.

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.

Now let’s take a look at the performance of our testing participants in other applications. One of the few real-life programs available for 32-bit as well as 64-bit mode is the PovRay 3.6 rendering system. We used the integrated benchmark to test the performance of our Pentium 4 processor supporting EM64T and Athlon 64 processor in Windows XP Professional x64 Edition (the higher score on the diagram indicates better result):

Here we see a completely different situation than the results of SiSoft Sandra 2005 SP1. Athlon 64 processor runs 25% faster with 64-bit AMD64 extensions involved than in 32-bit mode. Intel Pentium 4 with EM64T, on the contrary, loses about 25% of its speed in 64-bit mode.

The next benchmark we used for our performance investigation of Intel and AMD CPUs is a small Pi-Bench program, which calculates the pi-number as a sum of a series. The diagram below shows how long it took to complete this calculation with the given precision value.

In this case we see that 64-bit mode appears favorable for Athlon 64 as well as Pentium 4 with EM64T. However, the performance increase of Athlon 64 processor in 64-bit mode is a bit higher and equals 55%, while Pentium 4 managed to benefit by only 35% of extra performance.

One more task we are going to use today for benchmarking purposes is test file compression according to the zip-algorithm using zlib library. The diagram below shows how much time it took our testing participants to finish the task.

Again we witness a significant performance boost when we use the execution code optimized for 64-bit extensions of AMD64 and EM64T. In this case the performance increase by the CPU with AMD64 technology made 120%, while in case of a CPU with Intel EM64T technology the performance in 64-bit mode grew up by 65%. In other words, we once again see that AMD’s implementation of 64-bit extensions appeared more efficient than 64-bit extensions for x86 architecture from Intel.

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.


Well, CPUs supporting 64-bit extensions of the x86 architecture are currently available from both major CPU manufacturers. And they are going to be shipping in even bigger quantities in the nearest future. In other words, the first step towards mass transition to 64-bit applications has already been made. The second step in that direction will follow shortly. It will be the release of the 64-bit user operating systems, with Windows XP Professional x64 Edition being among the most important ones. After that 64-bit software and applications will start overwhelming the market. So, it looks like we will be witnessing a massive transition from the obsolete 32-bit architecture to the more advanced 64-bit one.

In fact, we haven’t yet fully faced the limitations imposed by the 32-bit mode, and the 4GB of RAM seem quite enough for any type of tasks. However, progress keeps going and very soon we will see that much RAM only by the entry-level systems. This is exactly when we are going to see true advantages of the 64-bit processors and operating systems.

However, we have to state that the entire infrastructure necessary for successful transition to 64-bit era is almost ready. The operating system ready to be released works just fine, even though it is still an RC1 revision. Most drivers have also been almost finalized by now. All we can do now is wait until Windows XP Professional x64 Edition comes out, which should happen in H1 2005.

A really big advantage of the new Windows XP Professional x64 Edition OS is its ability to allow smooth transition from 32-bit applications to 64-bit ones, because it supports both: usual 32-bit software and the new 64-bit programs. Moreover, our today’s test session showed that 32-bit programs are performed in Windows XP Professional x64 Edition without any significant performance losses. This way, if you are a happy owner of a CPU with AMD64 or EM64T support, you have green light to install Windows XP Professional x64 Edition. Just keep in mind that it still might be incompatible with some specific software and hardware, so you’d better double-check first.

As for the performance quality provided by the CPUs from AMD and Intel when processing 64-bit extensions, it is still too early to make any final verdicts about that. According to our preliminary testing in a very limited number of benchmarks, CPUs supporting AMD64 technology provide higher performance gain when working with 64-bit code than the CPUs supporting EM64T. However, the opposite is also true once there is proper optimization for the EM64T technology, and in this case we saw Intel processors show much better potential than the competitor’s solutions.

That is why I would for now refrain from voicing out any final conclusions about the winner on the hardware front. Software developers who continue working on 64-bit applications are now the ones the outcome of this duel depends on in the first place.