Thursday, March 26, 2020

Operating systems TRUE or FALSE Questions set 7

Operating systems TRUE / FALSE questions for competitive exams

Operating Systems Quiz with Answers - 7

1. A system that provides segmentation without paging puts holes in the physical address space, forcing the operating system to waste physical memory.
(a) TRUE                                                   (b) FALSE
Answer: FALSE. Segmentation potentially puts holes in the VIRTUAL space, but doesn’t require holds in the physical address space, since the segmentation mapping is free to use any contiguous blocks of memory. [source: UCB]

2. In a single processor system, the kernel can simply disable interrupts to safely access kernel data structures, and does not need to use any spin locks.
(a) TRUE                                                   (b) FALSE
Answer: TRUE. Spinlock results in an indefinite postponement until the thread holding the lock can finish and release it. Using spinlocks in multi-core processors are OK. [source: IITB]

3. Memory mapped I/O devices cannot be accessed by user-level threads.
(a) TRUE                                                   (b) FALSE
Answer: FALSE. Memory-mapped I/O is accomplished using load/store instructions to a special region of memory; a user-level thread can access this region if the user’s page table has a mapping for it. [source: UCB]

4. Consider N threads in a process that share a global variable in the program. If one thread makes a change to the variable, the change is visible to other threads.
(a) TRUE                                                   (b) FALSE
Answer: TRUE. The change will be visible to other threads. This is logical, since the process is the unit of resource management, not the thread. [source: IITB]

5. The rate of page faults in a virtual memory system can always be reduced by adding more memory.
(a) TRUE                                                   (b) FALSE
Answer: FALSE. There are circumstances in which adding memory can actually increase the number of faults. Specifically: Belady’s anomaly can come into play for a FIFO replacement policy and certain access patterns. [source: UCB]



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