Jawaharlal Nehru Technological University Hyderabad B.Tech III COMPUTER ORGANIZATION Previous Question Paper (October - 2020 - R16)

The design of a basic computer involves the integration of a Central Processing Unit (CPU), memory unit, and Input/Output (I/O) subsystem. The CPU consists of registers (PC, AR, IR, AC, DR), an Arithmetic Logic Unit (ALU), and a control unit that orchestrates data flow via a common bus system. Computer operation follows the fetch-decode-execute cycle.

The flow of operation is as follows:

1. Fetch: The instruction is read from memory at the address stored in the Program Counter (PC) and loaded into the Instruction Register (IR). The PC is then incremented.
2. Decode: The control unit decodes the opcode in the IR to determine the required operation.
3. Effective Address Calculation: If the instruction involves memory, the effective address is calculated.
4. Execute: The control unit generates the necessary control signals to perform the operation (e.g., addition, data transfer) using the ALU or data registers.
5. Interrupt Check: The system checks for pending interrupts before returning to the fetch stage.

A microprogram is a set of microinstructions stored in a control memory that defines the control signals for a processor's instruction set, essentially implementing the control unit's logic. A microprocessor is a complete central processing unit fabricated on a single integrated circuit, which includes the control unit, ALU, and registers to execute machine-level instructions.

Yes, it is possible to design a microprocessor without a microprogram using hardwired control. In a hardwired design, the control unit is implemented using fixed logic gates, flip-flops, and decoders. While hardwired control is significantly faster than microprogrammed control, it is less flexible, as changing the instruction set requires a complete redesign of the physical circuit hardware.