Multi-threaded microprocessors evolution or revolution

Abstract

Abstract. Threading in microprocessors is not new, the earliest threaded processor design was implemented in the late 1970s and yet only now is it being used in mainstream microprocessor architecture. This paper reviews threaded microprocessors and explains why the more popular option of outof-order execution has a poor future and is not likely to provide a pathway for future microprocessor scalability. The first mainstream threaded architectures are beginning to emerge but unfortunately based on out-of-order execution. This paper will review the relevant trends in multi-threaded microprocessor design and look at one approach in detail, showing how wide instruction issue can be achieved and how it can provide excellent performance, latency tolerance and above all scalability with issue width. This model exploits ILP and loop level parallelism using a vector-like instruction set in a chip multiprocessor. 1 The Forces at Play in ISA Design There are two forces that determine the form and function of microprocessor architectur