Itanium
The Itanium 64-bit microprocessor is developed jointly by Hewlett-Packard and Intel. It represents the goal of producing a "post-RISC era" high performance microprocessing architechture. It is referred to as a VLIW architechture, standing for Very Long Instruction Word. Its native instruction set is IA-64, but it can slowly run x86 code in a firmware emulation mode, and has hooks for PA-RISC family migration.
One of the biggest breaks that Itanium makes with current RISC design philosophy is that it completely depends on the compiler to optimize code. It has no facilities to execute instructions out of order. The compiler is expected to align instructions into specific "bundles" which are most efficiently executed by the processor. If the compiler cannot do this, performance suffers. Performance also suffers if the user runs the binary code on a processor with a different microarchitecture to the one for which the binary was compiled; this primarily affects proprietary software. The original idea behind this is cutting microprocessor hardware complexity by increasing compiler software complexity. As of 2002, there are two main problems with this idea: one is that Itanium is seemingly as complicated as many more traditional designs. The other, more important, one is that while dynamic scheduling in hardware has been done many times, designing an Itanium friendly compiler is a new art.
Software support for the Itanium is a work in progress, but Linux is a shipping platform, and work on NetBSD will begin when Itanium-based hardware ships. Proprietary operating systems being ported include include Microsoft Windows, HP/UX, Tru64, OpenVMS, and AIX. It remains to be seen how they overcome the limitations of microarchitecture-specific scheduling.
The Compaq / DEC Alpha, the HP PA-RISC family, and the SGI MIPS UNIX lines will eventually be retired in favor of Itanium hardware. With the exception of SGI's IRIX, the OS's running on these machines will remain similar.
As of 2001, Itanium has returned mostly disappointing performance numbers. The second generation Itanium slated for release in 2002 is said to be much more impressive. So far there are no concrete plans to introduce Itanium into the home PC market.
Critics of the Itanium processor have labeled it the "Itanic". Intel will be in a difficult position if the Itanium processor is a disappointment, as the need for 64-bit architecture in commodity servers is now pressing, and the need for a 64-bit architecture in personal computers is only a few years away, and a real archtectural threat now exists in the form of AMD's x86-64 architecture. AMD's x86-64 follows Intel's earlier behavior of extending a single architecture, first from the 8-bit 8088 to the 16-bit 8086, then from 16-bits to the 32-bit 80386 and beyond, without ever removing backwards compatibility. The x86-64 architecture extends the 32-bit x86 architecture by adding 64-bit registers, with a full 32-bit and 16-bit compatibility modes for earlier software. There are now pre-release versions of both Linux and the Microsoft Windows operating systems available for x86-84, together with early test silicon.