The Growth of Interest in Microprogramming: A Literature Survey
ACM Computing Surveys (CSUR)
Measures of Op-Code Utilization
IEEE Transactions on Computers
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A method, called conditional interpretation, is proposed which will allow small computers to have as large a set of instructions as may be desired without using a large number of bits to hold the operation code. The method is based on the redundancy of machine language instruction sequences. Most machine language instructions have a limited number of "reasonable" successors. For example "load accumulator" hardly ever follows "enter accumulator." It turns out that if each instruction is allowed seven successors plus an "escape instruction," only about one out of every five instructions needs to be an "escape" to get to one of the less usual successors. Seventy-five percent of the time the desired "next instruction" is among the seven permitted successors. Since each instruction has its own, possibly unique, set of successors, the interpretation of the stored op-code is conditional upon the state of the machine.