Operating Systems

Step 1: Analyze the definition of a process.
In computer science, a program is a passive collection of instructions. A process is the active instance of a computer program that is being executed by one or more threads. It contains the program code and its activity.

Step 2: Evaluate the given options.
(A) A reusable resource is hardware (like a printer) or software (like a library) that can be used by multiple processes, but it is not the process itself.

(B) A variable timer is a mechanism used for scheduling or managing time within the OS, but it is not a process.

(C) "Program in execution" is the standard definition of a process. It represents the dynamic execution of a program's code.

(D) Allocation and de-allocation of memory are functions performed by the operating system's memory manager, often on behalf of a process, but this is an action, not the process itself.

Conclusion: The correct definition is a program in execution.

Step 1: Define deadlock.
A deadlock is a state in which each member of a group of processes is waiting for some other member to release a resource. Since all processes are waiting, none of them can proceed, and they are stuck in a permanent state of waiting. This situation is also known as a circular wait.

Step 2: Evaluate the options based on the definition.
(A) This statement perfectly describes the deadlock condition, specifically the circular wait condition where Process 1 waits for a resource held by Process 2, and Process 2 waits for a resource held by Process 1.

(B) A process exceeding its time slice is handled by the scheduler, which will preempt the process. This is related to scheduling, not deadlock.

(C) Running out of memory is a memory management issue that can cause processes to fail or the system to slow down (thrash), but it is not a deadlock.

(D) A process entering the running state is a normal part of the process life cycle.

Conclusion: The defining characteristic of a deadlock is a set of blocked processes each holding a resource and waiting to acquire a resource held by another process in the set.