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AMD Athlon 64-Bit CPUs Explained


Ever since Advanced Micro Devices (AMD) launched the Athlon 64 processors late last year, there has been a bit of confusion about them all. With the two different chips being so similarly named, Athlon 64 and Athlon 64 FX, it's easy to understand the confusion. The purpose of this article is not to review the two chipsets, but is merely intended to help clear up some of the confusion around the Athlon 64 and Athlon 64 FX chips.

Some Basic Info
For those of you who keep up with technical code names, the "Hammer" chips are now known as the "AMD64 Platform" and "x86-64" is now known as "AMD64 ISA".

The "Athlon FX" is actually an abbreviated name for the chip, much in the same way that "Athlon XP" is. Currently, there is only one Athlon FX chip out, the FX-51, and because of this, most people (users and resellers alike) tend to leave off the -51 from the chip name. Hopefully once additional "FX" chips come out such as the FX-53 it'll help ease the confusion between the Athlon 64 chips and the Athlon 64 FX chips.

The Athlon 64 chips will continue to be named in the same way that the Athlon XP and MP processors were (e.g. Athlon 64 3000+, Athlon 64 3200+, Athlon 64 3400+, and so on). On more than one occasion, we've seen people refer to the processor's model number thinking that the number is an indication of the processor speed (e.g. Athlon 1800+ being 1.8Ghz) this of course is not true.

AMD uses the four-digit Model number as a "simple, accurate representation of relative AMD processor performance based on industry-standard software benchmarks. The higher the model number, the better the overall software performance running on the processor. The "+" at the end of each model number indicates the added performance benefits delivered by AMD's innovative processor designs, such as an integrated memory controller and HyperTransport technology."

Rather than using model numbers for the Athlon 64 FX processors, the 64 FX line will be using a "series numbers" (FX-51, FX-53, and so on)... In other words, a model number. The "FX" is the class designator for the processor, but also "alludes to the film industry's terminology for effects." "The number "51" is arbitrary. It is odd numbered on purpose. The odd numbers are different. They stand out from the norm, much like the processor."

The "64" in both processor names come from the processors ability to run the AMD64 instruction set that will be supported in Microsoft's future operating systems.

Since it has "64-bit" in the name, you would probably think that Microsoft Windows XP 64-Bit Edition Version 2003 would support the AMD64 instruction set, however Microsoft Windows XP 64-Bit Edition Version 2003 only officially supports Intel's Itanium 2 chip. "Windows XP 64–Bit Edition has been optimized specifically for the Intel Itanium processor and benefits from its key features." Not really a big deal since Windows XP 64-Bit Edition Version 2003 is currently available via MSDN (Microsoft Developer's Network) subscriber download, or if you buy an Itanium 2 system from HP with the OS pre-installed.

** Editor's Note (01/31/2004): It was previously reported in this article that Windows XP 64-Bit Edition officially supported the AMD64 instruction set, this information however is incorrect. Currently Microsoft does not support the AMD64 instruction set. Also the information about HP selling Windows XP 64-Bit has been corrected.

Windows XP Home, Windows XP Professional, and Windows Server 2003 do not support the AMD64 instruction set, but can still be used on AMD64 systems do to the 32-bit compatibility included with the processors. As of 01/23/2003 Microsoft has a Beta version of Microsoft Windows Server 2003 Enterprise Edition for 64-bit Extended Systems which supports the AMD64 instruction set. You can download a copy of it 100% free from Microsoft by going here.

For those of you who love Windows XP and don't want to bother with a server OS to use an AMD64 processor, there is good news, Microsoft has just released a trial version of Windows XP 64-Bit Edition for 64-Bit Extended Systems, which in short is Windows XP 64-Bit for AMD64 processors. You can download it 100% free from Microsoft by going here.

** Editor's Note (02/04/2004): Added information about Microsoft's Windows XP 64-Bit Edition for 64-Bit Extended Systems trial offer. I'd also like to note that the OS is currently not commercially available, and the trial version is good for 360 days. My guess is the OS will officially be released in the next 6-12 months, but there has been no word on that from Microsoft.

Microsoft Windows "Longhorn" (should it ever come out) and future Microsoft operating systems should support the AMD64 instruction set.

In addition to costly operating systems from Microsoft, several Linux distributions support the AMD64 instruction set. At the time this article was written SuSE Linux, Mandrake Linux, and Gentoo Linux have full support for the AMD64 and the Fedora (RedHat) Project has a Beta for Core 1 available.

** Editor's Note (01/31/2004): Added Gentoo Linux to the list of Linux distributions, as it was mistakenly left off. No, this wasn't a "pay back" for the problems I've had with Gentoo. :p

Not that anyone around here uses it, but Sun Microsystems plans on supporting AMD64 on its Solaris operating system sometime in the first quarter of this year. For those of you who don't know what Solaris is, Sun's version of Unix.

In addition to Sun Solaris, several variations of BSD Unix are in the process of supporting or being ported over to the AMD 64. These include FreeBSD, NetBSD, and OpenBSD.

In short, AMD64 based processors will "run all x86-based operating systems, including 32-bit versions of Microsoft Windows, Linux, and Solaris."

AMD has replaced the front-side bus in the Athlon 64 and Athlon 64 FX processors with a dedicated memory bus and a HyperTransport link. The HyperTransport link operates at 1600MHz.

So, what is HyperTransport technology? It's a new technology, that'll probably use the abbreviation HT and be confused with Intel's HyperThreading Technology. Technically speaking HyperTransport technology is "a new high speed, high performance link for integrated circuits (ICs) on a motherboard. It can be significantly faster than a PCI bus for an equivalent number of pins. HyperTransport was previously codenamed Lightning Data Transport, or LDT. HyperTransport technology was invented by AMD and perfected with the help of several partners throughout the industry. It is primarily targeted for the IT and Telecomm industries, but any application where high speed, low latency and scalability is necessary can potentially take advantage of HyperTransport technology. HyperTransport technology was invented in order to unleash the tremendous power of the AMD microprocessors. HyperTransport is planned to bring the computation experience to a new level."

Now that we've taken a look at all the basic information about the AMD64 processors, let's get into the technical detail, which I know is what many people are really after. ;)

** Editor's Note (01/31/2004): Information about the AMD Opteron may be added at a later date, but it should be noted that the AMD Opteron and AMD 64 FX-xx are basically the same chips. This will be explained in greater detail later.

  1. Introduction & Chip Information
  2. Athlon 64 FX-xx
  3. Athlon 64 xxxx+
  4. Side-by-side Comparison & Conclusion
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