What is the relationship between process states and the machine cycle?

Let us understand what a process state is and how it relates to the machine cycle.

Process States

Process states are the different stages in which a process exists during its lifetime. There are basically five states of processes −

• New − The process is about to be created but not yet created. It is the program present in secondary memory that will be picked up by the OS to create the process.

• Ready − The process enters the ready state after creation, meaning the process is loaded into main memory and waiting for CPU allocation.

• Running − The process is chosen by the CPU for execution and its instructions are being executed by one of the available CPU cores.

• Waiting − When the process requests access to I/O, needs input from the user, or requires access to a critical region, it enters the blocked or wait state.

• Terminated − Process is killed and its PCB (Process Control Block) is deleted.

Machine Cycle

A machine cycle is the basic operation performed by a central processing unit (CPU), which is the main logic unit of a computer. It consists of a sequence of steps performed continuously at a rate of millions per second while a computer is in operation.

The machine cycle has four main phases −

• Fetch − The control unit requests instructions from main memory at the location indicated by the program counter.

• Decode − The received instruction is decoded in the instruction register to determine what operation needs to be performed.

• Execute − The instruction's opcode specifies the CPU operation required. The actual computation or operation is performed.

• Store − The result is stored back to memory or registers, and the program counter is updated to point to the next instruction.

Relationship Between Process States and Machine Cycle

The relationship between process states and the machine cycle is fundamental to understanding how operating systems manage processes −

• Running State & Machine Cycle − When a process is in the running state, the CPU executes the machine cycle (fetch-decode-execute-store) for that process's instructions.

• Context Switching − When a process transitions from running to ready (preemption), the current machine cycle state must be saved in the Process Control Block so execution can resume later.

• I/O Operations − During the execute phase, if an instruction requires I/O operations, the process transitions to the waiting state until the I/O completes.

• Time Quantum − In time-sharing systems, a process may be preempted after completing several machine cycles, causing a state transition from running to ready.

Conclusion

Process states and machine cycles are interconnected concepts in operating systems. The machine cycle represents the CPU's execution mechanism, while process states manage which process gets access to this execution capability. Understanding this relationship is crucial for comprehending how operating systems achieve multitasking and resource management.