Jawaharlal Nehru Technological University Hyderabad B.Tech III COMPUTER ORGANIZATION Previous Question Paper (March 2021 - R16)

The instruction cycle is the fundamental sequence of operations a CPU performs to execute a single machine language instruction. It consists of the following primary phases:

1. Fetch: The CPU reads the next instruction from memory at the address stored in the Program Counter (PC). The instruction is loaded into the Instruction Register (IR), and the PC is incremented to point to the next instruction.
2. Decode: The control unit interprets the opcode in the IR to determine the required operation and identifies the necessary operands.
3. Execute: The CPU performs the actual operation, such as arithmetic, logic, or data movement, involving the ALU and registers.
4. Store/Write-back: The result of the execution is written back to the destination register or memory location if required.

If the instruction involves memory operands, an additional Indirect cycle may occur between decoding and execution to fetch the effective address of the operand.

A microprocessor is a physical integrated circuit (CPU) that executes instructions, whereas a microprogram is a set of microinstructions stored in a control memory used by the control unit to implement the instruction set architecture. Essentially, a microprocessor is the hardware component, while a microprogram is the software-like control logic within that hardware.

It is possible to design a microprocessor without a microprogram. Such designs use hardwired control, where the control unit is implemented using fixed logic gates, flip-flops, and decoders. Hardwired control is faster but less flexible than microprogrammed control.

Not all microprogrammed computers are microprocessors. A computer can be microprogrammed using discrete components or multiple chips rather than a single integrated circuit. Conversely, not all microprocessors are microprogrammed; many high-performance microprocessors use hardwired control to achieve higher clock speeds.