Understanding Process States and Queues in Operating Systems

In an operating system, a process goes through various states during its lifetime. These states typically include New, Ready, Running, Waiting (or Blocked), and Terminated. The question asks about a process that is "residing in main memory and ready and waiting for execution". Let's break down what this means and where such a process is held.

What is a Process?

A process is an instance of a program in execution. It requires resources like CPU time, memory, files, and I/O devices to complete its task.

Process States Explained

When a program is loaded into memory to become a process, it enters the Ready state. From the Ready state, it can transition to the Running state when the operating system's scheduler selects it for execution on the CPU. If a Running process needs to wait for an event (like I/O completion), it moves to the Waiting state. Once the event occurs, it moves back to the Ready state. When a process finishes execution, it moves to the Terminated state.

• New: The process is being created.
• Ready: The process is in main memory, waiting to be assigned to a processor.
• Running: Instructions are being executed by the processor.
• Waiting (or Blocked): The process is waiting for some event to occur (like I/O completion or signal).
• Terminated: The process has finished execution.

Understanding Different Queues

Operating systems use various queues to manage processes based on their current state.

• Job Queue: This queue holds all processes in the system. When a process is first submitted, it is placed in the job queue. Processes from the job queue are admitted to the system (usually loaded into main memory) and placed in the ready queue.
• Ready Queue: This queue holds processes that are in main memory and are ready to execute, waiting for their turn on the CPU. The operating system scheduler selects the next process to run from this queue.
• Wait Queue (or Device Queue): This queue holds processes that are waiting for a particular event, such as the completion of an I/O operation or the availability of a resource. There might be separate wait queues for different types of events or devices.

Analyzing the Question and Options

The question specifies a process that is "residing in main memory and ready and waiting for execution". Let's look at the options:

• Job Queue: Processes in the job queue are typically on disk, waiting to be loaded into main memory. This doesn't match the description of "residing in main memory".
• Execution Queue: This is not a standard term in most operating system contexts describing process queues. The term "execution" usually refers to the process being in the Running state on the CPU.
• Wait Queue: Processes in the wait queue are in main memory but are waiting for a specific event (like I/O). The question says "ready and waiting for execution", which implies waiting for the CPU, not an external event.
• Ready Queue: Processes in the ready queue are in main memory and are ready to be executed by the CPU. They are waiting for the scheduler to dispatch them. This perfectly matches the description "residing in main memory and ready and waiting for execution".

Therefore, a process residing in main memory and ready and waiting for execution is kept on the Ready Queue.

Revision Table - Process States and Queues

Additional Information - Scheduling and Dispatching

The operating system component responsible for selecting which process from the ready queue should be executed next is called the scheduler. The dispatcher is the module that gives control of the CPU to the process selected by the scheduler. This involves context switching, which is saving the state of the old process and loading the saved state of the new process. The management of processes through these queues and states is a fundamental part of operating system process management and scheduling.