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The Pentium 4 adds 64-bit Extensions

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Understanding the new Pentium 4 with support for 64-bit extension technology.
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The Pentium 4 adds 64-bit Extensions

Understanding the new Pentium 4 with support for 64-bit extension technology.


Intel has released new versions of the Pentium 4 with EM64T (Extended Memory 64 Technology) support, which use the same Socket 775 as other recent versions. These processors are designed for use in desktop PCs as well as single-processor workstations and servers, however the only systems which will really need this support are workstations and servers. This article discusses the 64-bit extensions as well as the chipsets designed to support the new processors.

Desktop PC vs. Workstation vs. Server

The differences between a workstation and a desktop PC are not always easy to describe since the boundaries can be vague. A workstation is basically an extremely high powered PC, however the line between them is somewhat fuzzy. For example, what were considered workstations a few years ago are in many ways less powerful than consumer level PCs today. Both desktop PCs and workstations are operated by a user with a keyboard and pointing device, and both use a monitor as their primary output device. However, workstations, particularly those used for tasks such as computer-aided-drafting, differ from PCs in the amount of RAM (typically 1GB or more), the type of graphics card used (higher-precision 3D card optimized for CAD), the processor speed (faster), and possibly the operating system. Workstations running Unix pioneered such innovations as very large displays and multiple display support that are now standard on recent PCs. 64-bit versions of Unix and its open-source clone, Linux, have been used by recent workstations, and with the development of 64-bit versions of Windows, Windows-based workstations can also use the larger memory address space and faster processing of large data sets which are characteristic of 64-bit operating systems.

Servers, which provide processing and storage services to multiple computers, benefit even more from 64-bit support, because the large memory and database sizes they support can be shared among many users. Large L2 cache sizes are also useful, as a large L2 cache minimizes the need to access the disk for new code or data segments.

64-bit Processors

Although there has been a lot of news about "new" 64-bit processors, they have actually been around for longer than most people realize. Intel and HP began development of the 64-bit Itanium processor in 1994 under the codename Merced.

After a long gestation period, the Itanium was finally introduced in May 2001. Still, this isn't really that significant for PCs because the Itanium is strictly considered a server/workstation processor and not a processor for use in desktop PCs.

Additionally, the IA-64 (Intel Architecture 64-bit) instruction set used by the Itanium is completely different from the IA-32 (Intel Architecture 32-bit) instruction set used by standard Intel and AMD PC processors, not to mention the cost of the Itanium kept it strictly in the server and workstation market.

The start of real 64-bit computing for standard PCs began on April 22, 2003 when the AMD Opteron processor was introduced. The Opteron did not use the IA-64 instruction set from the Itanium, but instead included 64-bit extensions that worked on top of the existing IA-32 instructions developed by Intel. This would allow for greater compatibility with existing software, and make it easier for 32-bit and 64-bit computing to coexist on the same platform. Unfortunately like Itanium, Opteron is also a server/workstation processor, considered far too costly for standard desktop or mobile PCs.

Up until this point all 64-bit processors were high end chips designed for servers and workstations, not your normal desktop PCs. What the industry really needed was a standard desktop PC processor that supported 64-bit extensions. This finally happened on September 23, 2003 when AMD released the Athlon 64, truly the first desktop PC processor supporting 64-bit extensions. This would be the breakthrough needed for any significant 64-bit software development to occur.

Although both the Opteron and Athlon 64 supported 64-bit extensions to the standard Intel 32-bit instructions, perhaps the most interesting feature was that AMD released these extensions before Intel. Collectively the computing world held its breath, waiting for the other shoe to drop. Would Intel release a different set of 64-bit extensions, essentially invalidating what AMD had done, or would they actually adopt the same extensions that AMD released first. On February 17, 2004 the answer came when Intel introduced the first Pentium 4 processors with 64-bit extensions, the very same extensions as first introduced by AMD. I for one am glad that Intel adopted the same extensions as AMD, as this would allow the same software to work on both AMD and Intel processors.

It is interesting to note that AMD calls these extensions AMD64 technology, while Intel calls them EM64T (Extended Memory 64 Technology). Microsoft and others also refer to these same extensions as x64, mainly to differentiate between them and the completely different IA-64 instructions used by the Itanium.

EM64T and AMD64 have a few minor technical differences which should prove to be inconsequential. As a consequence, when the first 64-bit commercial versions of Windows XP and desktop applications are introduced in 2006, they should support both processors equally well.

Evolution of the Pentium 4

The most significant difference between the new Pentium 4s and previous Pentium 4 models is their support for Intel's Extended Memory 64 Technology (EM64T). EM64T, which was first introduced by Intel's 3.6GHz Xeon processor with 800MHz front-side bus, is an extension of Intel's classic IA-32 32-bit architecture. EM64T enables processors to run 64-bit operating systems and access much larger amounts of memory and bigger databases while retaining full backwards compatibility with existing 32-bit and 16-bit operating systems and applications. 32-bit processors can work with a maximum of 4GB of RAM, while EM64T can work with as much as 256TB (terabytes; a terabyte is over 1 trillion bytes) of addressable memory. In practice, while actual 64-bit systems include much lower amounts of memory, many 64-bit workstations include 16GB of RAM. Unlike Intel's initial 64-bit processors, the Itanium and Itanium 2, which use a processor architecture known as IA-64, EM64T-compatible processors can run existing 32-bit and 16-bit code at full processor speed.

EM64T is similar to AMD's AMD64 64-bit processor technology. AMD64, introduced by AMD's Athlon 64 and Opteron processor families, is the first 64-bit architecture based on 32-bit Intel-compatible (x86) processor architecture. Although EM64T and AMD64 have a few differences, EM64T was based on AMD64 commands and adds some Intel-specific commands such as SSE3. As a consequence, when the first 64-bit commercial versions of Windows XP and desktop applications are introduced in 2005, they'll support both processors equally well.

Processor Details

Initially, Pentium 4 processors supporting EM64T are available at clock speeds ranging from 3.2GHz (3.20F) to 3.8GHz (3.80F).

All are based on the latest 90-nanometer process, support hyperthreading (HT Technology), feature 800MHz FSB and 1MB of L2 cache and use Intel's latest processor socket, Socket 775. Note the "F" designation in the frequency, which indicates EM64T support. This can be used especially on boxed processors to distinguish those with EM64T vs. those without.

Another way to determine that you are getting a processor with EM64T is to check the sSpec number on the chip. Because Intel makes several different processors in these speed ranges, it's useful to know the processor model number and sSpec number for these processors (see Table 1).

Table 1 – Intel Pentium 4 Processors Supporting EM64T

Clock Speed


Model Number


















*Other Pentium 4 Model processors with the same model number do not support EM64T.

Be sure to use either the "F" designation in the frequency or the sSpec of the processor to determine if it supports EM64T. If you don't know the processor's sSpec number but you have the OEM or retail order codes, you can use the Intel Processor Spec Finder http://processorfinder.intel.com to display only Pentium 4 processors of a particular clock speed. Click on each sSpec number to display OEM or retail order codes and other information.

It is important to note that native EM64T operation requires not only a processor with EM64T support, but also a chipset, ROM BIOS, 64-bit operating system, and 64-bit device drivers as well. Even more important than that is the fact that a processor supporting EM64T will not work at all (even in 32-bit mode) unless the BIOS and chipset also support EM64T. This means that for example if you purchase a "3.80F" processor, you need to insure that the motherboard (chipset and BIOS) supports EM64T. If you have a processor and motherboard which support EM64T, you can still run existing 32-bit OS, drivers and applications if desired, in that case the chip will remain in 32-bit mode.

Workstation and Server Chipsets for the Pentium 4

As the world's leading provider of chipsets for its processors, Intel has rolled out new desktop/workstation and server chipsets for Socket 775. The desktop/workstation chipset is the 925X Express, which is also the top-of-the-line item in Intel's new line of PCI-Express desktop chipsets. The 925X Express supports PCI-Express x16 (video) and x1 (general-purpose) slots, high-definition audio (7.1 speaker support), dual-channel DDR2 memory, USB 2.0 ports, Serial ATA and matrix storage.

The server chipset is the E7221, originally known as Copper River), which also supports PCI-Express, but uses PCI-Express much differently than the 925X Express chipset. The E7221 uses PCI-Express to provide support for PCI-Express x8, which in turn supports a 64-bit PCI hub with built-in support for PCI-X slots at speeds up to 133MHz. PCI-X support is essential for high-performance SCSI arrays and very fast server-optimized network adapters. Instead of using PCI-Express x16 for video, the E7221's MCH integrates SVGA video (which is all that a server requires). As befits a server, the E7221 also supports ECC RAS advanced memory error correction, PCI-X and PCI hot-plug replacement, and can switch automatically from dual-channel to single-channel memory support if one memory channel (device) fails.

Figure 1 shows the major features of the 925X chipset, while Figure 2 shows the major features of the E7221 chipset.

Figure 1Figure 1

Figure 2Figure 2


By adding 64-bit support to the Pentium 4 family, Intel has finally created a rival to the popular AMD Athlon 64. This new group of Pentium 4 processors will enable desktops as well as workstations and entry-level servers to enjoy 64-bit "Intel Inside" processing when 64-bit versions of Windows XP Professional and applications become available at retail (mostly likely in 2006).

For Further Research

Intel Resources

Intel's official Extended Memory 64 Technology website provides links to EM64T technical documentation and FAQs


The official website for the Intel 925X Express chipset (workstation) http://developer.intel.com/design/chipsets/925X/workstn.htm

The official website for the Intel E7221 Server chipset http://developer.intel.com/design/chipsets/e7221/index.htm

Third-Party Resources

This MaximumPC article reprint discusses how Intel used 'clean-room' engineering to support the AMD64 instruction set with its own EM64T technology http://www.maximumpc.com/reprints/reprint_2004-06-01b.html

You can learn more about AMD64 by reading my article on the AMD Opteron: http://www.quepublishing.com/articles/article.asp?p=339076

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