538 THE PROCESSOR-MEMORY-SWITCH (PMS) NOTATION

Control, K. A component that evokes the operations of other components in the system. All other components are taken to consist of a set of discrete operations, each of which, when evoked, accomplishes some discrete transformation of state.

With the exception of a processor, P, all other components are essentially passive and require some other active agent (a K) to set them into small episodes of activity.

Switch, S. A component that constructs a link between other components. Each switch has associated with it a set of possible links, and its operations consist of setting some of these links and breaking others.

Transducer, T. A component that changes the i-unit used to encode a given meaning (i.e., a given referent). The change may involve the medium used to encode the basic bits (e.g., voltage levels to magnetic flux, or voltage levels to holes in a paper card), or it may involve the structure of the i-unit (e.g., bit-serial to bit-parallel). Note that T's are meaning-preserving (in number of bits), since the encodings of the (invariant) meaning need not be equally optimal.

Data-operation, D. A component that produces i-units with new meanings. It is this component that accomplishes all the data-operations, e.g., arithmetic, logic, shifting, etc.

Processor, P. A component that is capable of interpreting a program in order to execute a sequence of operations. It consists of a set of operations of the types already mentioned (M, L, K, S, T, and D) with the control necessary to obtain instructions from a memory and interpret them as operations to be carried out.

Each component has a set of attributes and associated values and takes on the form:

There are alternative, shorthand ways of saying the same thing when the attribute names are clear. For example: