JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II COMPUTER ORGANIZATION Previous Question Paper (December - 2018 - R16)

Instruction types in a computer system are categorized based on the operations they perform. The generic instruction types are:

• Data Transfer Instructions: These instructions move data between memory and processor registers, or between registers. Examples include LOAD, STORE, MOVE, PUSH, and POP.
• Data Manipulation (Arithmetic and Logical) Instructions: These perform computational tasks on data. Arithmetic instructions include ADD, SUBTRACT, MULTIPLY, and DIVIDE, while logical instructions include AND, OR, XOR, NOT, and bitwise shifts or rotations.
• Program Control (Branching) Instructions: These change the sequence of instruction execution by modifying the Program Counter (PC). Examples include JUMP, CALL, RETURN, and conditional branches like JUMP IF ZERO.
• Input/Output (I/O) Instructions: These facilitate the transfer of data between the processor and external peripheral devices.

In computer architecture, the distinction between direct and indirect addressing lies in how the instruction specifies the location of the operand.

• Direct Addressing: The instruction contains the actual effective address of the operand in memory. The CPU uses the address field provided in the instruction directly to access the data. This requires only one memory reference to fetch the operand.
• Indirect Addressing: The address field in the instruction refers to a memory location that contains the effective address of the operand, rather than the operand itself. This requires two memory references: the first to retrieve the address from the specified location, and the second to fetch the actual data.

The difference is summarized by the number of memory accesses required:

While direct addressing is faster due to fewer memory cycles, indirect addressing provides greater flexibility, such as implementing pointers or accessing large memory spaces that exceed the instruction's address field capacity.