Intel 64

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Intel 64 is the x64 implementation of the IA-32 - x86 architecture from Intel that it claims . a. enables more than 4 GiB of RAM to be addressed directly . The instruction set extension is largely compatible with AMD64 from AMD and is fundamentally based on it.

Earlier terms were " E xtended M emory 64 T echnology", abbreviated EM64T and IA-32e .


Due to the market success of the AMD64 processors and the growing ranks of AMD64 software, Intel decided that for quite some time under the codename Yamhill and Clackamas Technology developed Intel 64 (earlier names were IA32e or EM64T) permanently in the NetBurst architecture to integrate. CPUs with this microarchitecture, Xeon processors “Nocona” from June 2004, were able to execute the extended x86 instructions known as AMD64, which was the original 32-bit architecture “ Intel Architecture 32-Bit ”, or IA for short -32, into a 64-bit x86 architecture (x86-64 or x64 for short ).

Intel had spoken out against AMD64 for a long time because it did not want to endanger the position of its own 64-bit Itanium architecture "IA-64". If Intel had its way, the Itanium architecture, which is incompatible with the x86 architecture, would have been launched on the market as the exclusive 64-bit architecture. The marketing name of the instruction set was appropriately referred to as " Intel Architecture 64-Bit ". Since AMD was able to bring many well-known OEM manufacturers into the AMD64 boot in the meantime and the massive switch to 64-bit in desktop and workstation computers was in full swing at that time, almost all observers assumed that the AMD64 would be the would become the most significant 64-bit architecture. So Intel had to give in to the pressure of the market because Microsoft, among others, did not want to maintain two 64-bit versions of its Windows operating system for client systems. IA-64 versions of Windows client systems that had already been delivered were no longer developed after the switch to Intel 64. Since April 2010, the new development of the server software for the IA-64 architecture has also been stopped, which can be attributed to falling demand.

The line of mobile processors was also expanded to include Intel 64 with the Core 2 processors introduced in 2006 . They represent the departure from the NetBurst architecture and were also used in desktop and server machines.

Differences from AMD64

Some machine commands behave differently with Intel 64 than with AMD64 or do not exist at all. However, the details of the differences from AMD64 are mainly relevant to compiler and operating system developers .

  • The first versions of the EM64T implementation lacked the machine commands LAHFand SAHF. This fact only became relevant with later operating systems such as Windows from version 8.1 , as these now require these 64-bit machine commands. (However, the 32-bit version of Windows will continue to run, with its limitations.)
  • Another difference between AMD64 and Intel 64 CPUs is the IOMMU unit , which is optional with Intel 64 . While the IOMMU unit called AMD-Vi is always present on AMD64 processors , it is absent on some processor models from Intel, where it is called VT-d . This means that no direct memory access ( DMA ) from devices that do not support 64-bit addressing (especially 32-bit PCI devices) to memory areas above 4 GiB are possible. Instead, the kernel has to emulate this capability in software and first write the data to buffers below the 4 GiB limit . Linux , for example, does this with the software bounce buffering function ( SWIOTBLmanually via kernel parameters iommu=soft).

CPUs with Intel 64

Individual evidence

  1. Christof Windeck: EM64T is now called Intel 64. In: Heise online . September 28, 2006 . Retrieved January 6, 2018.
  2. Christof Windeck: Microsoft no longer programs new Itanium software. In: Heise online . April 6, 2010 . Retrieved January 6, 2018.
  3. Bestofmedia Team: Upgrading And Repairing PCs 21st Edition: Processor Specifications. IA-32e 64-Bit Extension Mode (x64, AMD64, x86-64, EM64T). Tom's Hardware, October 14, 2013, p. 5 , accessed on January 6, 2018 (English): "Note: Early versions of EM64T-equipped processors from Intel lacked support for the LAHF and SAHF instructions used in the AMD64 instruction set. However, Pentium 4 and Xeon DP processors using core steppings G1 and higher completely support these instructions; "
  4. IOMMU SWIOTBL. In: Gentoo Linux Wiki. Accessed February 28, 2018 .

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