Single-cycle CPU refers to a simple computer processor, and its simplicity lies in that all instructions can be completed in only one clock cycle. This kind of processor is often used in academic research or special application fields. Compared with multi-cycle CPU, the design of single-cycle CPU is simpler, which can save hardware cost and execute instructions faster.

The running process of single-cycle CPU can be simply summarized as two steps, namely, fetching instructions and executing instructions. In the instruction fetch stage, the CPU reads instructions from memory into the instruction register. In the instruction execution stage, the CPU will operate the data according to the type of the instruction and store the operation result in a register or a memory. The whole process can be completed in only one clock cycle. Although the design of single-cycle CPU is simple, it can't process complex instruction sequences quickly.

One-cycle CPU can be used in the learning and teaching of assembly language, because its instruction set and running process are relatively simple and easy to understand and realize. In addition, because single-cycle CPU can execute simple instructions quickly, it is also widely used in some specific application fields, such as Internet of Things equipment and control systems. However, it should be noted that single-cycle CPU is not competent for high-performance application scenarios, so it is rarely used in large computers or high-performance computers.