An Instruction Set also known as Instruction set architecture (ISA) is the abstract model present in a computing machine that gives the instruction to the CPU present in a computer machine. The computing machine performs the required operations. The Operating System and Applications communicates to the computing hardware to perform an action through the Instruction Set. The instructions tell the processor what operations to perform, such as arithmetic, data manipulation, and input/output operations.
Complex instruction set computer (CISC) is a large set of complex instructions to perform multiple operations.
Reduced instruction set computer (RISC) is small and highly optimized set of instructions to perform operations within a a clock cycle.