Which of the following queues keeps a set of all processes residing in main memory ready and waiting to execute?
Ready queue
Understanding Process Queues in Operating Systems
In an operating system, processes move between different states (like New, Ready, Running, Waiting, Terminated). To manage these processes efficiently, the OS uses various queues. These queues hold processes that are waiting for a specific resource or an event to occur before they can proceed.
Key Process Queues Explained
Let's look at the queues mentioned in the options:
- Job Queue: This queue holds all processes that are in the system. When a new process arrives, it is initially placed in the job queue. These processes might be waiting to be loaded into main memory.
- Ready Queue: This queue holds processes that are residing in main memory and are ready and waiting to be assigned to a CPU for execution. Processes in the ready queue are in the "ready" state.
- Device Queue: Each device has its own device queue. Processes that are waiting for a particular I/O device (like a disk drive or printer) are placed in the device queue for that device.
- Task Queue: This term is sometimes used more generally, often in the context of systems like thread pools or asynchronous processing, where units of work (tasks) are queued for processing. In the traditional context of operating system process management, "Ready queue" is the specific term for processes ready to run on the CPU after being loaded into memory.
Analyzing the Question
The question specifically asks for the queue that keeps a set of all processes "residing in main memory" and "ready and waiting to execute". Let's compare this description with the queues we defined:
- The Job queue holds processes that might not be in main memory yet.
- The Device queue holds processes waiting for I/O devices, not necessarily ready to execute on the CPU.
- The Ready queue holds processes that are in main memory and are ready to execute on the CPU.
The description perfectly matches the definition of the Ready queue.
Summary of Queues
| Queue Name | Description | Process Location/State |
|---|---|---|
| Job Queue | All processes in the system, waiting for admission to memory. | Secondary Storage (usually), New state |
| Ready Queue | Processes in main memory, ready and waiting for CPU. | Main Memory, Ready state |
| Device Queue | Processes waiting for a specific I/O device. | Main Memory, Waiting state |
Based on the analysis, the queue that holds processes residing in main memory, ready and waiting to execute, is the Ready queue.
Revision Table: Operating System Queues
Reviewing the different queues helps solidify understanding of process management in operating systems.
- Job Queue: System's entry queue for new processes.
- Ready Queue: Processes in RAM, prepared for CPU time.
- Device Queue: Processes paused, awaiting I/O completion.
Additional Information: Process States and Scheduling
The concept of queues is closely linked to process states and CPU scheduling. When a process is in the 'Ready' state, it is in the Ready queue. The CPU scheduler selects one process from the Ready queue to move it to the 'Running' state, where it is executed by the CPU. If a running process needs I/O, it moves to a 'Waiting' state and is placed in a Device queue. Once the I/O is complete, it moves back to the 'Ready' state and is placed back in the Ready queue.
Important Questions from Process Scheduling
An OS follows round-robin scheduling with time quantum of 4ms. Assuming that the CPU is free now and there are 20 processes waiting in the ready queue, the maximum amount of time that a process waits before getting into the CPU is _________.
- Match the LIST-I with LIST-IIChoose the correct answer from the options given below:
LIST-I LIST-II A. Short term scheduler I. Determine which process are added to the system for execution level place them in ready queue. B. Medium term scheduler II. Select which process should be executed next and allocate CPU time. C. Long term scheduler III. Manage the degree of multi programming by swapping processes between main memory and disk storage D. I/O Scheduler IV. Order the input/output requests from processes waiting for I/O operations.
