In an instruction format, which field explicitly specifies what operation the CPU must perform?

Introduction / Context:
Machine instructions are composed of fields that the CPU decodes to execute operations. Understanding which field directs the CPU's action is foundational to assembly language, microarchitecture, and compiler back ends.

Given Data / Assumptions:

• An instruction format typically includes an opcode plus zero or more operand specifiers.
• The question seeks the field that tells the CPU 'what to do'.
• Standard terminology is assumed.

Concept / Approach:

The operation code (opcode) identifies the operation such as add, load, branch, or compare. Operand address fields then specify sources and destinations. Control logic in the CPU decodes the opcode and generates control signals to route data and invoke the appropriate functional units.

Step-by-Step Solution:

Verification / Alternative check:

Any ISA manual (e.g., ARM, x86) lists opcodes and their meanings; the decoder interprets opcodes to drive execution units.

Why Other Options Are Wrong:

• Address: points to operands; it does not define the operation.
• Locator: nonstandard term here.
• Flip-Flop: a bistable storage element, unrelated to instruction fields.
• None of the above: incorrect since 'Operation code' is correct.

Common Pitfalls:

• Assuming addressing mode bits dictate the operation; they only affect operand interpretation.

Final Answer:

Operation code.