When a process needs to use the CPU, what state must it be in?

For a process to utilize the CPU, it must be in the "Ready" state. The Ready state indicates that the process is prepared to execute and is waiting for CPU time. These processes have all necessary resources allocated and are simply awaiting their turn to be assigned to the CPU by the operating system's scheduler.

When a process is in the Blocked state, it cannot execute until some event occurs, such as the completion of I/O operations, meaning it is not ready to use the CPU at that moment. The Running state, on the other hand, indicates that the process is currently executing instructions on the CPU, so it doesn’t need to request CPU time. The Terminated state signifies that the process has completed its execution and is no longer eligible for CPU use. Thus, the only state in which a process can readily use the CPU when it is scheduled is the Ready state.