IA-64

IA-64 (Intel Itanium architecture) is the instruction set architecture (ISA) of the discontinued Itanium family of 64-bit Intel microprocessors. The basic ISA specification originated at Hewlett-Packard (HP), and was subsequently implemented by Intel in collaboration with HP. The first Itanium processor, codenamed Merced, was released in 2001. The Itanium architecture is based on explicit instruction-level parallelism, in which the compiler decides which instructions to execute in parallel. This contrasts with superscalar architectures, which depend on the processor to manage instruction dependencies at runtime. In all Itanium models, up to and including Tukwila, cores execute up to six instructions per cycle. In 2008, Itanium was the fourth-most deployed microprocessor architecture for enterprise-class systems, behind x86-64, Power ISA, and SPARC. In 2019, Intel announced the discontinuation of the last supported CPUs for the IA-64 architecture. Microsoft Windows versions from Server 2003 to Server 2008 R2 supported IA-64; later versions did not support it. The Linux kernel supported it for much longer but dropped mainline support by version 6.7 in 2024 (while still supported in Linux 6.6 LTS). Only a few other operating systems, such as HP-UX, OpenVMS, FreeBSD, ever supported IA-64; HP-UX's support ended in December 2025; OpenVMS still supports it, FreeBSD discontinued support in FreeBSD 11. T2 Linux still supports IA-64 via an out-of-tree kernel patch.