  The appearance and disappearance of coprocessors by integration into the CPU,
the success or failure of coprocessors are examined by summarizing their
characteristics from the mainframes of the 1960s. The coprocessors most
particularly reviewed are the IBM 360 and CDC-6600 I/O processors, the Intel
8087 math coprocessor, the Cell processor, the Intel Xeon Phi coprocessors, the
GPUs, the FPGAs, and the coprocessors of manycores SW26010 and Pezy SC-2 used
in high-ranked supercomputers in the TOP500 or Green500. The conditions for a
coprocessor to be viable in the medium or long-term are defined.
