VLIW (Very Long Instruction Word) - processor arcitecture designed to exploit instruction level parallelism (ILP).
Processors based on VLIW architecture can execute many instructions in the same time. Theese instructions are located into long instruction words. In contrast with superscaler architectures, VLIW requires instructions to be staticly put in long words. That makes the CPU more simple, but all the work on determining the instruction parallelism is put on the compiler. That makes a good optimizing compiler nessesary for good performance and the compiler construction becomes very complex.
First implementations of VLIW processors were made in late 1980s by the company Cydrome but it failed. In 1990s HP also researched VLIW-based processors.
In 1989 Intel introduced i860 - the first 64 bit and the first VLIW CPU. This chip did not archive commercial success and the project was closed in 1990. In 2001 Intel and HP intrduced Itanium processor based on IA-64 architecture. It was based on modified VLIW architecture called EPIC.
In 2000 Transmeta introduced the Crusoe CPU based on VLIW. Its notable feature was executing x86 instructions by using some sort ov virtual machine.
In 2007 MCST introdused the processor Elbrus that has its own VLIW based architecture. Working on this model line MCST later developed the processors Elbrus-2S+, Elbrus-4S and announced the 8-core VLIW processor Elbrus-8S. Theese processors also can execute x86 instructions using binary translation.
Beside general-purpose processors VLIW also had some usage in GPU systems. For example the AMD Radeon HD 2900 XT GPU had shader processor based on VLIW.
