In operating systems, what is a deadlock in the context of processes competing for resources?

Introduction / Context:
Deadlock is a classic problem in operating systems where processes compete for exclusive resources. When a deadlock occurs, affected processes stop making progress even though the system is still running. Understanding the formal definition of deadlock is important for learning detection, prevention and avoidance techniques such as resource ordering and the Bankers algorithm.

Given Data / Assumptions:

Processes need resources such as CPU, memory, files and I O devices.
Some resources are non sharable and can be held by only one process at a time.
Processes may request additional resources while already holding some resources.
The question is about the precise meaning of deadlock in this resource allocation setting.

Concept / Approach:
A deadlock is a circular waiting situation. Each process in a group holds one or more resources and waits for other resources that are currently held by other processes in the same group. Because no process is willing to release its resources until it obtains the ones it is waiting for, the system reaches a standstill. Without external intervention, the processes remain blocked forever. This permanent blocking distinguishes deadlock from ordinary temporary delays.

Step-by-Step Solution:
Step 1: Consider two processes, each holding a resource and requesting the other resource. Neither process can proceed, because each is waiting for the other to release its resource. Step 2: Generalize this idea to any number of processes and resources where a circular wait exists. Step 3: Recall the four necessary conditions for deadlock: mutual exclusion, hold and wait, no preemption and circular wait. Step 4: Recognize that in a deadlock, the processes are permanently blocked; they cannot finish their tasks without outside action such as killing a process or preempting resources. Step 5: Match this behaviour with the definition given in the correct option, which describes a set of processes holding and waiting for resources in a circular way.

Verification / Alternative check:
Operating system textbooks define deadlock using almost the same wording as the correct option, emphasizing permanent blocking and circular resource dependency. Simple I O delays, intensive CPU use or normal shared printer usage are not classified as deadlocks because they do not involve a circular hold and wait pattern that persists indefinitely.

Why Other Options Are Wrong:
A temporary delay caused by a slow device eventually clears, so it is not permanent blocking.
High CPU usage by a process that still makes progress is a performance issue, not a deadlock.
Normal queued access to a printer may involve waiting, but the queue advances and each process eventually prints, so there is no circular wait.

Common Pitfalls:
Learners sometimes label any kind of waiting or performance slowdown as deadlock. Another mistake is to forget that deadlock involves a group of processes, not just one. Always check for circular waiting over non sharable resources and for the fact that the processes cannot proceed without external intervention.

Final Answer:
A deadlock is a situation where a group of processes are permanently blocked because each holds some resources and waits for additional resources held by other processes in the same group, creating a circular wait.