Computer architecture — instruction format basics: In machine language, the first field of an instruction that specifies the operation to be carried out (for example, add, load, jump) is called the __________.

Introduction / Context:
Every processor executes binary instructions that are broken into fields. The field that tells the CPU what action to perform is critical because it determines which hardware pathways (datapath and control) activate. This question checks if you know the name of that instruction field in true machine language terminology.

Given Data / Assumptions:

• The discussion refers to binary machine language, not assembly syntax.
• An instruction typically contains an operation field and one or more operand/addressing fields.
• Examples of operations include arithmetic, logic, data movement, and control flow.

Concept / Approach:
The operation code (abbreviated as opcode) is the part of the instruction that selects which operation the CPU performs. Control logic decodes the opcode into control signals. The remaining bits (operands, immediate data, or addressing mode specifiers) provide the data or references needed to complete the operation.

Step-by-Step Solution:

Verification / Alternative check:
Open any ISA reference (e.g., 8085, x86, ARM). The term “opcode” consistently labels the bits that select an instruction operation. Assemblers translate human mnemonics like MOV or ADD into opcodes.

Why Other Options Are Wrong:

• mnemonic: Assembly-language shorthand for humans; not a machine field.
• interrupt: An external or internal event that diverts execution; not an instruction field.
• instruction cycle: A timing concept for fetch/execute; not a field inside an instruction.
• operation counter: Not a standard term in ISA documentation.

Common Pitfalls:
Confusing assembly mnemonics (text) with opcodes (binary). Assuming “first part” always means a fixed-length field—some ISAs use variable-length opcodes but the role is unchanged.

Final Answer:
opcode