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AMD64 is the original x64 implementation of the IA-32 - x86 architecture, which runs on x86 processors from AMD et al. a. enables more than 4 GiB of RAM to be addressed directly . The instruction set extension has been developed for the K8 generation by AMD since 1999 and was available in 2003 with the Opteron server processors.

Intel 64 is the expansion for x86 processors from Intel that is largely compatible with AMD64.


There were already numerous 64-bit processors around by the 1990s. The x86 processor, which is mainly used in PCs , was expanded in 1985 with the Intel 80386 from a 16-bit to a 32-bit architecture . Due to a license exchange agreement between Intel and AMD, both companies were able to use each other's extensions in their own x86 processors.

At the end of the 1990s, Intel also wanted to enter the business with 64-bit processors, but developed a new processor architecture that had nothing to do with x86. On October 4, 1999, Intel introduced the first "Itanium" processor, the result of this joint work with HP.

To underline that the Itanium architecture was to succeed the IA-32 -x86 architecture, Intel called it "IA-64" - "Intel Architecture 64-Bit." IA-32 referred to as "Intel Architecture 32-Bit." “Already the x86 architecture of the i386, ie 32-bit x86.

AMD countered with a counter-draft that was based on the existing 32-bit x86 architecture IA-32 and was supposed to expand it with a 64-bit mode: On October 5, 1999, one day after the Itanium presentation, AMD announced that to work on an instruction set extension under the title x86-64 . In contrast to Intel's 64-bit Itanium / IA-64 architecture , AMD's design was based on conventional 32-bit processors with an IA-32 instruction set, whose registers were widened in 64-bit mode. This means that x86-64 is fully downwardly compatible with the previous 32-bit and even the 16-bit architecture . However, the greatest advantage in 64-bit mode turned out to be the doubling of the available registers, so that with x86-64 not only can a larger memory area be addressed, but in some cases performance improvements can be achieved solely through the wider registers.

In August 2000, AMD delivered an initial specification, showing that a smooth transition from 32 to 64 bit environments was possible while modernizing the x86 architecture.

Intel initially did not participate in the x86-compatible 64-bit expansion and concentrated fully on Itanium (IA-64), of which the first processors were already available in 2001. However, Itanium didn't really get going - since the IA-64 architecture was not compatible with x86 (IA-32), the software had to be written for it first, which cost valuable time.

At AMD, it took until April 2003 until the first Opteron processors with the 64-bit extension, renamed AMD64, were available, but these were very well received by the market. Existing 32-bit x86 software also ran in 64-bit mode without having to be changed, and with the Opteron processors, AMD achieved significant participation in the x86 server market.


From the mid-2000s, AMD64 (formerly x86-64) and Intel 64 (formerly EM64T) were also increasingly integrated into desktop processors. Just like all processors after the AMD-K8 - from AMD as well as the Intel Core microarchitecture from Intel offer the 64-bit instruction set extension. Since AMD64 and Intel 64 are almost identical, the designation “x64” for 64-bit x86 or 64-bit “IA-32” has established itself alongside “amd64” - also in contrast to the incompatible “Intel Architecture 64” -Bit “IA-64 of the Itanium from Intel and HP, which has not been further developed since 2016.

Due to the many very similar names, the development name x86-64 has also been retained, especially for architecture names. For example, kernels of Unix operating systems ( e.g. Linux or XNU ) displayuname -m this name when entering , but with an underscore instead of a hyphen. Without a precise context, x86_64or "x86-64" denotes both the implementation of AMD - "AMD64" - and that of Intel - "Intel 64."

In summary, it can be said that the terms x64 and x86-64 basically stand for both AMD64 and Intel 64. In the context of software, however, amd64 (mostly in lower case) also stands for both implementations.


The following models have an implementation of the AMD64 architecture:

Web links

Individual evidence

  1. Michael Kanellos: Intel Names Merced Chip Itanium. In: CNET October 4, 1999, accessed August 7, 2013 .
  2. AMD Discloses New Technologies at Microprocessor Forum. In: press release. AMD, October 5, 1999, accessed November 9, 2010 .
  3. AMD Releases x86-64 Architectural Specification; Enables Market Driven Migration to 64-Bit Computing. In: press release. AMD, August 10, 2000, accessed November 9, 2010 .