Computer Architecture : CISC Processors

A computer processing a large number of instruction is known as a Complex Instruction Set Computer termed as CISC. The CISC approach attempts to minimize the number of instructions per program, sacrificing the number of cycles per instruction. Computers based on the CISC architecture are designed to decrease the memory cost. Because, the large programs need more storage, thus increasing the memory cost and large memory becomes more expensive. To solve these problems, the number of instructions per program can be reduced by embedding the number of operations in a single instruction, thereby making the instructions more complex.

Ths instructions in a normal CISC processor give direct manipulation of operands present in memory. The main goal of a SISC architecture is to give us a single machine instruction for each statement that is written in a high-level language. Some Examples of CISC architecture are the Digital Equipment Corporation VAX computer, IBM 370 computer, intel 80486 etc.

The major characteristics of CISC architecture are as given below :
  1. Contains a large number of instruction.
  2. Instruction-decoding logic will be Complex.
  3. One instruction is required to support multiple addressing modes.
  4. Few instructions that does the particular tasks and are used often.
  5. It contains instructions that manipulate operands in memory.
  6. Various CISC designs are set up two special registers for the stack pointer, handling interrupts,  etc.
  7. Micro programmed control unit is found in CISC.

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