JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II COMPUTER ORGANIZATION AND ARCHITECTURE Previous Question Paper (August/September - 2022 - R18)

Computer Architecture refers to the conceptual structure and functional behavior of a computer system as perceived by the programmer. It focuses on the logical attributes, such as the instruction set, number of bits used for data representation, addressing modes, and I/O mechanisms. Essentially, it defines what the machine does.

Computer Organization refers to the operational units and their interconnections that realize the architectural specifications. It deals with the hardware details, such as control signals, memory technology, physical interfaces, and clock signals. Essentially, it defines how the machine is implemented.

Key differences include:

• Architecture is concerned with the design of the system from the user's perspective, while Organization is concerned with the hardware implementation.
• Architecture defines the instruction set and data types, whereas Organization defines how these instructions are executed by the hardware.
• Architecture is relatively stable over time, while Organization changes as technology advances (e.g., using faster transistors or different cache structures).

An instruction code is a group of bits that instructs the computer to perform a specific operation. The format of an instruction is typically divided into two main parts: the Opcode (Operation Code) and the Operand.

The Opcode field specifies the operation to be performed, such as ADD, LOAD, or STORE. The number of bits in the opcode depends on the number of instructions in the instruction set; for instance, 4 bits can represent up to 16 distinct operations.

The Operand field specifies the data to be operated on or the address where the data is located. Depending on the architecture, the instruction format may also include:

• Mode bits: These define the addressing mode (e.g., direct, indirect, or indexed addressing).
• Register specifiers: These identify which registers are involved in the operation.

A common instruction format is represented as:

The total length of the instruction code is determined by the word size of the processor, ensuring that the entire instruction can be fetched from memory in a single cycle.