Intel64AMD64

Intel64 and AMD64 refer to the 64-bit extensions of the x86 processor architecture developed by Intel and AMD, respectively. The umbrella term for these extensions is x86-64. Intel64 and AMD64 describe the two vendor-specific implementations that are largely binary-compatible at the instruction set level, allowing software written for 32-bit x86 to run on 64-bit processors with minimal changes.

AMD introduced AMD64 in 2003 with the Opteron and Athlon 64 families, creating a seamless 64-bit extension to the x86 architecture while preserving backward compatibility with 32-bit software. Intel later adopted the technology, initially branding it EM64T and later Intel 64; the two implementations are designed to be functionally compatible, enabling shared software ecosystems and operating systems.

Architecturally, the 64-bit extensions introduce long mode, enabling operation in two modes: a 64-bit mode for native 64-bit software and a compatibility mode for running 32-bit code. The architecture expands general-purpose registers to 64 bits (with additional registers such as R8–R15) and extends addressing and memory management, supporting large virtual and physical address spaces. It uses a paging system with four levels and enhances performance through new instruction sets and SIMD extensions (such as SSE2 and AVX). Virtualization features (such as Extended Page Tables) are also supported, improving efficiency for virtualized environments.

Software and ecosystem support is broad, with major operating systems including Windows, Linux, and macOS providing 64-bit kernels and user-space libraries. The two implementations are largely interoperable, enabling a wide range of applications, development tools, and optimizations that leverage the capabilities of modern 64-bit processors from both vendors.