True 64 bit processor (contrary to AMD64 and EM64T, being 64 bit extensions to the IA-32 architecture).
EPIC architecture (Explicitly Parallel Instruction Computing): tight coupling between hardware (processor) and software (compiler).
Performance depending on compilers generating efficient code (Instruction Level Parallellism, ILP), requiring more intelligence in the compiler back-end.
Itanium Instruction Set Architecture (ISA), Itanium System Environment (ISE).
Initiated by HP in 1990 (code name PA-WideWord, PA-WW), jointly developed by Intel and HP from 1993, originally as a follow-up to their respective X86 and PA-RISC processors. Other processors that would be obsoleted by Itanium were DEC/Compaq Alpha and SGI MIPS.
Itanium has problems gaining market share since its introduction in 2001. Back then, the first items were two years delayed. Its performance was poor, in particular of the IA-32 compatibility unit, which was buggy as well. SMP configurations (Symmetric Multi-Processing) were limited to four processors. And not enough native Itanium applications were available.
This forced HP to extend its PA-RISC roadmap with an extra generation (8900 series), and forced SGI to add even another two generations to its MIPS roadmap.
Sun cancelled its Solaris port for Itanium. And with Linux emerging, IBM, SCO, and Sequent cancelled their joint effort to combine their respective AIX, UnixWare, and PTX UNIXes into a single operating system (Monterey-64).
Finally, after AMD introduced 64 bits extensions (AMD64) to its processors, Intel was forced to follow with EM64T, pushing Itanium further up and away from the server market segment dominated by Intel Xeon and AMD Opteron processors.
Nowadays, all HP engineers working on Itanium have been transferred to Intel.
Itanium is only sold in high-end server and High Performance Computing (HPC) markets.
Since IBM and Dell dropped the Itanium servers from their product portfolios in 2005, by far most of the Itanium systems are being sold by HP. That makes Itanium mostly a replacement for HPs Alpha (DEC/Compaq) and PA-RISC processors, competing against IBM Power and Sun/Fujitsu UltraSparc. Other manufacturers selling Itanium systems are Bull, Fujitsu, Hitachi, NEC (together with Unisys), and SGI.
Today, Itanium is supported by Linux (Trillian, Red Hat, and SuSE), Compaq Tru64 Unix (HP), and HP-UX of course. Currently SGI is in a transition from its traditional IRIX on MIPS systems to Linux on Itanium.
Longhorn Server will support Itanium only for specific workloads: databases, custom jobs, and line-of-business applications.
In 2005, the companies currently manufacturing or selling Itanium hardware founded the Itanium Solutions Alliance, to promote the availability and acceptance of Itanium solutions in the market.
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