Lecture 3 RISC-CISC characterstics and difference.pptx
- 1. Lecture 3
- 2. Topics to Be Covered • Characteristics of RISC • Characteristics CISC • Difference Between RISC and CISC • Example of RISC and CISC
- 3. Reduced Instructions Set Computer(RISC) Characteristics of RISC architecture are • There are few instructions in the RISC architecture • One machine cycle is required to fetch the operands from registers, performs the ALU operation and than again stores it to the register. • For all the operations it should be from register to register. Other than LOAD, STORE most of the instructions are register to register. • RISC architecture uses the simple addressing modes. If required complex modes can be first converted into simple addressing modes. • It uses simple instruction format. Length of the instruction is fixed.
- 4. Complex Instruction Set Computer(CISC) Characteristics of CISC : •Large number of instructions •Large variety of addressing modes is used to address the complex instructions. •Instruction format in CISC is of variable length. Length of operation code and addressing field can be changed. •It fetches the information from memory. Registers are used only in limited operations.
- 5. Difference between RISC and CISC RISC CISC Simple instruction Complex instructions Only one cycle per instruction Multiple cycles per instruction Instruction executed by hardware Instruction interpreted by the microprogram Instruction format is simple and of fixed length Complex and variable length instruction format Simple addressing modes Complex addressing modes Complexity in the complier Complexity in the microprogram Multiple register sets Single register set
- 6. Example 1 2 3 4 1 2 X 3 Y 4 Main Memory Location RISC LOAD A, 2:2 LOAD B, 3:3 PROD A:B STORE 2:2, A CISC MUL 2:2, 3:3