Multiple Instruction and Single Data stream (MISD)

In this association, multiple processing elements are structured under the control of multiple control units. Each control unit is handling single instruction stream and processed through its corresponding processing element. But single processing element is processing only a one data stream at a time. Hence, for handling single data stream and multiple instruction streams, multiple processing elements and multiple control units are organised in this classification. All processing elements are relate with the common shared memory for the organisation of one data stream as given  in Figure 6. The only identified instance of a computer capable of MISD operation is the C.mmp built by Carnegie-Mellon University.

This type of computer organisation is denoted as:

                                                                      I_s > 1

                                                                      D_s = 1

This classification is not popular in commercial machines as the thought of single data streams implementing on multiple processors is rarely functional. But for the particular applications, MISD organisation can be very useful. For example, Real time computers need to be fault tolerant where several processors implement the same data for producing the redundant data. This is also called as N- version programming. All these redundant data are measured to as results which should be similar; otherwise faulty unit is returned. Thus MISD machines can be useful to fault tolerant real time computers.