Definition
Single-cycle Instruction
A single-cycle instruction is an instruction whose execute stage completes in one clock cycle.
Typical examples are integer addition, subtraction, bitwise operations, and address computation for loads and stores. The operation fits within a single cycle at the target clock frequency.
Compared to multi-cycle
A single-cycle instruction never causes the execute-busy stall that a multi-cycle instruction triggers. It is the common case in a RISC pipeline: most instructions pass through execute in one cycle, and only a few operations require multiple cycles.