Abstract: An information processing system includes a processor responsive to instructions for performing operations. The processor includes instruction queue for fetching and storing instructions in advance of execution and the system is responsive to certain of the instructions for causing execution of a corresponding sequence of instructions. A prefetch monitor includes circuitry for detecting instructions which may result in the execution of a corresponding sequence of instructions. The prefetch monitor further includes an instruction substitution circuit which is responsive to the detecting circuitry for inhibiting the reading of following instructions from a memory to the processor and is responsive to instruction fetching operation of the processor for reading null instructions to the processor.

Abstract: Emulation method and apparatus allowing a first system, which is not designed as a functional duplicate of a second system, to emulate the second system. The input/output structure of the second system is emulated in the first system by means of routines stored therein and which direct the already existing input/output structure to operate in the same manner as the input/output structure of the second system. The emulation routines are in turn invoked through the non-maskable interrupt mechanism of the first system by a modification thereto which detects the occurrence of "foreign" input/output requests; that is, input/output requests occuring in programs originally written for the second system and which are not normally recognized by the first system.