Intel Itanium

Intel Itanium (also called IA64, IA-64, I64, PA-WW and IPF) is a 64-bit processor architecture and corresponding processor family created by HP and Intel during the 90s and first released in 2001. Shipping with a significant delay, Itanium achieved moderate success between years 2002 and 2006, then slowly faded into obscurity, only kept alive for HP's Integrity platform running HP-UX, before it was finally discontinued in 2021. Its most prominent feature is the use of VLIW-like explicit parallelism (EPIC), where the compiler selects which instructions should be run in parallel (instead of the CPU itself, as is common in RISC).

In the late 90s, Itanium was believed to be a revolutionary concept that will take over most areas on computing; because of that, many hardware and software vendors planned to support it, often abandoning their original architecture and porting their operating system to Itanium. These include IBM, SGI, DEC/Compaq, Bull, HP, SuperMicro, Sun, Dell, Tandem and Secure64. This led to Itanium being viewed by some as an unfortunate mistake that killed most RISC platforms or even a conspiracy by Intel.

Itanium CPUs can be generally divided into three generations: Itanium 1, Itanium 2 and Itanium 9xxx. The 2001 Itanium 1, codenamed Merced, didn't deliver the expected performance - not many machines were made before it being replaced with Itanium 2 a year later. Itanium 2, codenamed McKinley, caught up and was adopted by many vendors including IBM, Dell and SGI, but that didn't last very long. By the release of the first 9xxx CPU, codenamed Montecito, Itanium became an HP-only architecture.