Abstract: Apparatus for improving the efficiency of computer instructions which transfer data from memory to machine registers and from machine registers to memory. The difficulty arises because such instructions may require data transfers of a variable number of bytes, may involve transfer across word boundaries within memory, and may use a number of machine registers. These features are important to programs which process variable amounts of data at different storage locations. Such transfer operations are performed by "mini-instructions", which are a proper subset of instructions that already exist within the current repertoire. However, the "mini-instructions" used are limited in the use of variables to only those which make most effective use of the hardware architecture. One or more "mini-instructions" must be used to execute the actual software instruction. Because the mini-instructions needed are a proper subset of the actual software instruction, little additional hardware is required.

Abstract: Apparatus and method which provides a variable instruction stack. Instructions to be executed are fed into a single input multiple output stack register feeding from the lowest to the highest level. Instructions are provided with a valid bit to distinguish instructions requiring execution from those requiring no execution (NOOP). When an instruction not requiring execution (NOOP) propagates to the highest level, the execution unit receives an instruction in a lower level of the stack avoiding any idle time of the execution unit waiting for an executable instruction to propagate to the highest level.