Operating Systems

The stack of the thread and its register context are deallocated when the thread terminates. Deallocation is the process of freeing the resources that were allocated to the thread during its execution. When a thread completes its execution, its resources, such as memory and registers, are released. Hence, this process takes place at the termination of the thread. Deallocation does not take place at the time of blocking, spawning, or unblocking the thread, because in those situations, the thread is either temporarily halted or waiting to be executed. Thus, the correct answer is: (1) at the termination of thread.

Unsegmented unpaged memory (A): In this type of memory, the virtual address is the same as the physical address, and no paging or segmentation is done. So, the correct match is (A) - (III). Unsegmented paged memory (B): Memory is viewed as a collection of logical address spaces, and paging is used to divide the address space. The correct match is (B) - (II). Segmented unpaged memory (C): Memory is divided into segments, and there is no paging. Virtual memory is viewed as a collection of segments. The correct match is (C) - (IV). Segmented paged memory (D): Memory is divided into both segments and pages. This means that memory is viewed as a paged linear address space. The correct match is (D) - (I). Thus, the correct option is: 1.(A) - (III), (B) - (II), (C) - (IV), (D) - (I).

- (A): True. Segmentation divides memory into variable-sized segments and represents the user view of memory. - (B): True. In paging, physical memory is divided into fixed-sized blocks called pages. - (C): False. In paging, logical memory is divided into pages, while frames refer to blocks in physical memory.

- (A) Disk scheduling → (II) SCAN: Disk scheduling algorithms like SCAN are used for optimizing disk access. - (B) Batch processing → (IV) FIFO: Batch processing processes jobs in First-In-First-Out (FIFO) order. - (C) Time sharing → (I) Round robin: Time sharing systems use round-robin scheduling to allocate CPU time. - (D) Interrupt processing → (III) LIFO: Interrupts are often handled in a Last-In-First-Out (LIFO) manner.

1. Shortest Job First (SJF): Execution order: P2, P4, P3, P5, P1. P4 starts after P2, so its waiting time = 18 ms. 2. Non-preemptive Priority Scheduling: Priority order: P2, P5, P3, P1, P4. P4 starts after all higher-priority processes, so its waiting time = 3 ms. 3. Round Robin (Quantum = 1): Round-robin execution: P1, P2, P3, P4, P5 (time slices). P4’s first time slice occurs after all processes get their first turn, so its waiting time = 1 ms.

- (A): True. Job schedulers (long-term schedulers) manage the process pool by moving processes into memory for execution. - (B): True. Short-term schedulers manage ready-to-execute processes and allocate the CPU. - (C): False. Medium-term schedulers manage memory but do not directly increase the degree of multiprogramming. They suspend and resume processes to manage memory.