In CPU scheduling, what is a ready queue and what kind of processes are stored in it at any given time?

Introduction / Context:
The ready queue is one of the central concepts in CPU scheduling. It represents the set of processes that are prepared to run but are temporarily not using the processor. Understanding what belongs in the ready queue helps you reason about scheduling algorithms and system performance. This question focuses on the definition and role of the ready queue in an operating system.

Given Data / Assumptions:

• Multiple processes reside in main memory at the same time.
• Only one or a few processors are available to execute them.
• The scheduler must choose which process to run next.
• Processes can be in states such as running, ready or blocked.

Concept / Approach:
The ready queue contains processes that are fully loaded into main memory and have all the resources they need to run except the CPU. These processes are not waiting for I O operations or other events; they are simply waiting for their turn to use the processor. The short term scheduler selects a process from the ready queue and dispatches it to the CPU. When a running process is preempted or voluntarily yields the CPU, it often returns to the ready queue to wait again.

Step-by-Step Solution:
Step 1: Distinguish between processes that are ready to run and those that are blocked on I O or events. Step 2: Recognise that only ready processes are eligible candidates for immediate CPU allocation. Step 3: Note that these processes are already in main memory and do not need additional resources besides the CPU. Step 4: Understand that the ready queue is the data structure that stores these candidates for scheduling. Step 5: Select the option that explicitly defines the ready queue as a list of processes in memory waiting only for CPU time.

Verification / Alternative check:
Operating system state transition diagrams show processes moving from the ready queue to the running state and back, or from running to blocked and later back to ready. In these diagrams, the ready queue is always associated with the short term scheduler and CPU dispatch, confirming that it contains processes prepared to execute but not currently running. This matches the correct option and not the options that describe job queues or blocked queues.

Why Other Options Are Wrong:
Option B confuses the ready queue with the job queue, which holds jobs that have not yet been admitted to memory. Option C describes terminated processes, which are no longer scheduled and therefore not part of the ready queue. Option D describes blocked processes that are waiting for I O or other events, which are held in separate wait queues rather than in the ready queue.

Common Pitfalls:
A typical confusion is to assume that any non running process is in the ready queue. In reality, only those that could run immediately if given the CPU belong there. Blocked processes waiting on I O or synchronisation primitives are stored elsewhere. Keeping these distinctions clear is essential for understanding scheduling and performance analysis.

Final Answer:
The ready queue is a list of processes that are in main memory, have all required resources except the CPU and are waiting to be scheduled for execution.