How RISC instruction sets are defined

RISC is the abbreviation of "Reduced instruction set Computing" in English, meaning "simplified instruction set" in Chinese.

It is developed on the basis of the CISC instruction system, and some people test the CISC machine to show that the use frequency of various instructions is quite disparity, the most commonly used is some simple instructions, they only accounted for 20% of the total number of instructions, but the frequency of the program appears to account for 80%. Complicated instruction system will inevitably increase the complexity of the microprocessor, so that the development of the processor time is long and the cost is high. and complex instructions require complex operations that will inevitably degrade the speed of the computer. For the above reasons, the the 1980s RISC CPU was born, as opposed to the CISC-type CPU, RISC-type CPU not only streamlined the instruction system, but also adopted a so-called "superscalar and super Pipeline structure", greatly increasing the parallel processing capacity.

RISC instruction set is the development direction of high performance CPU. It is relative to the traditional CISC (complex instruction set). In comparison, RISC's instruction format is unified, the type is less, and the addressing method is less than the complex instruction set. Of course the processing speed is much improved. At present in the high-end server commonly used in this instruction system CPU, especially high-end servers are all using RISC instruction system CPU. RISC instruction system is more suitable for high-end server operating system UNIX, now Linux also belongs to the Unix-like operating system. RISC CPUs are incompatible with the software and hardware of Intel and AMD CPUs.

At present, in the high-end server using RISC instruction CPU mainly has the following categories: PowerPC processor, SPARC processor, PA-RISC processor, MIPS processor, Alpha processor.