Computer Organization and Architecture

Prepared by : Prof. Khushbu Chauhan Computer Engg. Dept..

Outlines. Basic Instruction Cycle and Instruction set Formats and addressing Processor Organization and Register Organization Instruction Pipelining Co-processors Pipeline processors RISC and CISC computers..

Basic Instruction Cycle. A program consisting of the memory unit of the computer includes a series of instructions. The program is implemented on the computer by going through a cycle for each instruction. In the basic computer, each instruction cycle includes the following procedures − It can fetch instruction from memory. It is used to decode the instruction. It can read the effective address from memory if the instruction has an indirect address. It can execute the instruction. After the four procedures are done, the control switches back to the first step and repeats the similar process for the next instruction. Therefore, the cycle continues until a Halt condition is met. The figure shows the phases contained in the instruction cycle..

Registers Involved In Each Instruction Cycle Following are the different types of registers involved in each instruction cycle: •Memory address registers (MAR):It is connected to the addresslines of the system bus. It specifies the address in memory for a read or write operation. •Memory Buffer Register (MBR): It is connected to the datalines of the system bus.It contains the value to be stored in memory or the last value read from the memory. •Program Counter(PC):Holds the address of the next instruction to be fetched. •Instruction Register(IR):Holds the last instruction fetched..