1. An information processing system, comprising: a program storage unit in which a program that is to be executed is stored; at least two processors each of which executes at least one instruction; an executability information storage unit in which executability information, which includes information specifying each instruction as being executable or not executable by each of the at least two processors, is stored for each of the at least two processors; and a control unit that, at the time of execution of the program, selects at least one processor for execution of at least one instruction necessary to execute the program, from among the at least two processors, with reference to the executability information stored in the executability information storage unit, and causes the selected at least one processor to execute the instruction.