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3.2 Pipelines     continued...

Pipelines have been widely used in high performance machines for many years. The CDC 6600 is a classic example of a complex instruction pipeline, using a circuit known as a ``scoreboard'' to detect data dependencies between instructions and instruction buffers to implement pipelining in the fetch-decode logic. The Cray-1 was a very successful early supercomputer in which every data processing unit was pipelined. Until the late 1980s pipelining was one of the attributes that separated ``mainframes'' and supercomputers from microprocessors, but with the advance of VLSI technology microprocessors now have room on chip for complex control circuitry. Most now have pipelined data processing units and complex instruction scheduling logic that rivals that of the CDC 6600, an early pipelined processor known for its innovative instruction processing.