x86-64 or AMD64

x86-64 is a 64-bit superset of the x86 instruction set architecture. Because the x86-64 instruction set is a superset of the x86 instruction set, all instructions in the x86 instruction set can be executed by central processing units (CPUs) that implement the x86-64 instruction set; therefore those CPUs can natively run programs that run on x86 processors from Intel, Advanced Micro Devices (AMD), and other vendors.
x86-64 was designed by AMD, who have since renamed it AMD64. It has been cloned by Intel under the name Intel 64 (formerly known as EM64T among other names).^[1] This leads to the common use of the names x86-64 or x64 as more vendor-neutral terms to collectively refer to the two nearly identical implementations.

x86-64 should not be confused with the Intel Itanium architecture, also known as IA-64, which is not compatible on the native instruction set level with the x86 or x86-64 architecture.

Linux x86-64

See also: List of 64-bit Linux distributions

Linux was the first operating system kernel to run the x86-64 architecture in long mode, starting with the 2.4 version prior to the physical hardware's availability.

Linux also provides backward compatibility for running 32-bit executables. This permits programs to be recompiled into long mode while retaining the use of 32-bit programs. Several Linux distributions currently ship with x86-64-native kernels and userlands. Some, such as SUSE, Mandriva and Debian GNU/Linux package both 32-bit and 64-bit systems on a single DVD-ROM image to allow automatic selection of the best software during installation.
Other distributions, such as Ubuntu, are available in a version compiled for 32-bit and one compiled for x86-64 architecture.

64-bit Linux allows up to 2⁴⁷ bytes (128 TiB) of address space for individual processes, and can address approximately 2⁴⁶ (64 TiB) of physical memory, subject to processor and system limitations.

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• 1 AMD64
  • 1.1 History of AMD64
  • 1.2 Architectural features
  • 1.3 Virtual address space details
  • 1.4 Operating modes
    • 1.4.1 Operating mode explanation
  • 1.5 Implementations
• 2 Intel 64
  • 2.1 History of Intel 64
  • 2.2 Implementations
• 3 Differences between AMD64 and Intel 64
  • 3.1 Recent implementations
  • 3.2 Older implementations
• 4 Operating system support
  • 4.1 Windows
  • 4.2 Linux
  • 4.3 Mac OS X
  • 4.4 BSD
    • 4.4.1 FreeBSD
    • 4.4.2 NetBSD
    • 4.4.3 OpenBSD
  • 4.5 MenuetOS
  • 4.6 Solaris
  • 4.7 DOS
• 5 Industry naming conventions