Vector processing is intimately associated with the concept of a "supercomputer". As with most architectural techniques for achieving high performance, it exploits regularities in the structure of computation, in this case, the fact that many codes contain loops that range over linear arrays of data performing symmetric operations.
The origins of vector architecure lay in trying to address the problem of instruction bandwidth. By the end of the 1960's, it was possible to build multiple pipelined functional units, but the fetch and decode of instructions from memory was too slow to permit them to be fully exploited. Applying a single instruction to multiple data elements (SIMD) is one simple and logical way to leverage limited instruction bandwidth.
(To Be Continued...)