next up previous

3.1.3 MISD Computers

There are few machines in this category, none that have been commercially successful or had any impact on computational science. One type of system that fits the description of an MISD computer is a systolic array, which is a network of small computing elements connected in a regular grid. All the elements are controlled by a global clock. On each cycle, an element will read a piece of data from one of its neighbors, perform a simple operation (e.g. add the incoming element to a stored value), and prepare a value to be written to a neighbor on the next step.

One could make a case for pipelined vector processors fitting in this category, as well, since each step of the pipeline corresponds to a different operation being performed to the data as it flows past that stage in the pipe. There have been pipelined processors with programmable stages, i.e. the function that is applied at each location in the pipeline could vary, although the pipeline stage did not fetch its operation from a local control memory so it would be difficult to classify it as a ``processor.''