RISC [Reduced Instruction Set Computer]

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  • RISC processors only use simple instructions that can be executed within one clock cycle.
  • Thus, the "MULT" command described above could be divided into three separate commands: 
    • "LOAD," which moves data from the memory bank to a register,
    • "PROD," which finds the product of two operands located within the registers
    • "STORE," which moves data from a register to the memory banks. 
                        LOAD A, 2:3
                      LOAD B, 5:2
                      PROD A, B
                      STORE 2:3, A
  • More RAM is needed to store the assembly level instructions.
  • The compiler must also perform more work to convert a high-level language statement into machine code. 
  • To execute each instruction, if there is separate electronic circuitry in the control unit, which produces all the necessary signals.
  • It is also called hard-wired approach. 
  • pipelining: a techique that allows for simultaneous execution of parts, or stages, of instructions to more efficiently process instructions; 
  • large number of registers:
  • Examples of RISC processors: 
    • IBM RS6000, MC88100 
    • DEC’s Alpha 21064, 21164 and 21264 processors 

Features of RISC Processors: 

  • RISC processors use a small and limited number of instructions.
  • RISC machines mostly uses hardwired control unit. 
  • RISC processors consume less power and are having high performance. 
  • Each instruction is very simple and consistent. 
  • RISC processors uses simple addressing modes. 
  • RISC instruction is of uniform fixed length. 

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