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RISC (Reduced Instruction Set Computer)
Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.
Microprocessors have instruction sets called microcode that programmers use to create low-level computer programs. The instruction sets perform various tasks, such as moving values into registers or executing instructions to add the values in registers. Microcode can be either simple or complex, depending on the microprocessor manufacturer's preference and the intended use of the chip.
RISC designs, as the name implies, have a reduced set of instructions that improve the efficiency of the processor, but require more complex external programming. RISC designs are based on work performed at IBM by John Cocke. He found that about 20 percent of a computer's instructions did about 80 percent of the work. His 80/20 rule spawned the development of RISC architecture, which reduces the number of instructions to only those that are used most. The other instructions must be implemented in external software.
RISC processors have been used in network switches and routers to handle packet processing. Another processor design is the ASIC (application-specific integrated circuit) architecture. While switches with RISC processors use software-based algorithms, ASICs are hardware-based devices with switching matrixes and processing functions put directly in hardware. This improves performance and lowers cost, but ASICs cannot be upgraded like software-based systems.
Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.