Single instruction, multiple data: Difference between revisions

Revision as of 12:51, 25 July 2025

Revision as of 13:09, 25 July 2025

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The first use of SIMD instructions was in the [[ILLIAC IV]], which was completed in 1972. This included 64 (of an original design of 256) processors that had local memory to hold different values while performing the same instruction. Separate hardware quickly sent out the values to be processed and gathered up the results.

SIMD was the basis for [[vector processor|vectorVector supercomputers]] of the early 1970s such as the [[CDC STAR-100|CDC Star-100]] and the [[TI Advanced Scientific Computer|Texas Instruments ASC]], which could operate on a "vector" of data with a single instruction. Vector processing was especially popularized by [[Cray]] in the 1970s and 1980s. Vector processing architectures are now considered separate from SIMD computers: [[Duncan's Taxonomy]] includes them whereas [[Flynn's Taxonomy]] does not, due to Flynn's work (1966, 1972) pre-dating the [[Cray-1]] (1977). The complexity of Vector processors however inspired a simpler arrangement known as [[SIMD within a register]].

The first era of modern SIMD computers was characterized by [[massively parallel processing]]-style [[supercomputer]]s such as the [[Thinking Machines Corporation|Thinking Machines]] [[Connection Machine]] CM-1 and CM-2. These computers had many limited-functionality processors that would work in parallel. For example, each of 65,536 single-bit processors in a Thinking Machines CM-2 would execute the same instruction at the same time, allowing, for instance, to logically combine 65,536 pairs of bits at a time, using a hypercube-connected network or processor-dedicated RAM to find its operands. Supercomputing moved away from the SIMD approach when inexpensive scalar [[multiple instruction, multiple data]] (MIMD) approaches based on commodity processors such as the [[Intel i860|Intel i860 XP]] became more powerful, and interest in SIMD waned.<ref>{{cite web|url=http://www.cs.kent.edu/~walker/classes/pdc.f01/lectures/MIMD-1.pdf|title=MIMD1 - XP/S, CM-5}}</ref>