1. In a digital computer system including processor means responsive to instructions received in said processor means, said instructions including an operation code syllable containing an operation code and operand syllables representing items of data processed by said processor means and said processor means including operation code interpretation means responsive to said operation codes for controlling said processor means and operand interpretation means controlled by said operation code interpretation means for interpreting said operand syllables, means for responding to certain said instructions having variable numbers of said operand syllables comprising: (1) a number of operands specifier in said operation code syllable of each of said certain instructions for specifying said number of operand syllables in said certain instruction; and (2) means in said operation code interpretation means responsive to said number of operands specifier in a received said certain instruction for causing said operand interpretation means to interpret said number of operand syllables specified by said number of operands specifier in said received certain instruction.