With a neat diagram explain basic operational concepts of computer?
COMPUTER ORGANIZATIONExplanation
BASIC OPERATIONAL CONCEPTS -
• The processor contains ALU, control-circuitry and many registers.
• The instruction-register(IR) holds the instruction that is currently being executed.
• The instruction is then passed to the control-unit, which generates the timing-signals that determine when a given action is to take place
• The PC(Program Counter) contains the memory-address of the next-instruction to be fetched & executed.
• During the execution of an instruction, the contents of PC are updated to point to next instruction.
• The processor also contains „n‟ general-purpose registers R0 through Rn-1.
• The MAR (Memory Address Register) holds the address of the memory-location to be accessed.
• The MDR (Memory Data Register) contains the data to be written into or read out of the addressed location.
Following are the steps that take place to execute an instruction -
• The address of first instruction(to be executed) gets loaded into PC.
• The contents of PC(i.e. address) are transferred to the MAR & control-unit issues Read signal to memory.
• After certain amount of elapsed time, the first instruction is read out of memory and placed into MDR.
• Next, the contents of MDR are transferred to IR. At this point, the instruction can be decoded & executed.
• To fetch an operand, it's address is placed into MAR & control-unit issues Read signal. As a result, the operand is transferred from memory into MDR, and then it is transferred from MDR to ALU.
• Likewise required number of operands is fetched into processor.
• Finally, ALU performs the desired operation.
• If the result of this operation is to be stored in the memory, then the result is sent to the MDR.
• The address of the location where the result is to be stored is sent to the MAR and a Write cycle is initiated.
• At some point during execution, contents of PC are incremented to point to next instruction in the program. [The instruction is a combination of opcode and operand].
