Multiprogramming makes efficient use of the CPU by overlapping the demands for t
ID: 3861446 • Letter: M
Question
Multiprogramming makes efficient use of the CPU by overlapping the demands for the CPU and I/O devices from various users. Privileged instructions cannot be executed in monitor mode. An interrupt vector contains the saved program counter values of interrupted user programs. Direct memory access (DMA) requires a special controller that facilitates the transfer of blocks between the I/O device and main memory. If a kernel is single-threaded, system calls from any thread can block the entire task. We can prevent users from accessing other user's programs and data by introducing base and limit registers that hold the smallest physical memory address and the size of range of the user program respectively. An operating system can have both microkernel and virtual machine structures. There are solutions to synchronization problems that can be implemented using monitors, but cannot be implemented using semaphores. Long-term scheduler (or job scheduler) selects which processes should be brought into the ready queue and balances load for better throughput. When designing a multithreaded application, you must use synchronization primitives to make sure that the threads do not overwrite each other's registers. Small time slices always improve the average turnaround time of all the processes in a system. An OS uses multilevel feedback queues for process scheduling and a process in this OS needs 40ms for execution. If the first queue uses 2ms time quantum and for each level time quantum of the level is time quantum of previous level plus 5ms. a process will finish processing in fifth (5^th) level. (Suppose that the level with 2ms quantum time is the first queue).Explanation / Answer
1. True. In mutliprogramming multiple programs (and/or), multiple users share the CPU, so by overlapping the demands of I/O devices and CPU, the efficiency of CPU is increased.
2. False. Privileged instructions are always executed in the Monitor mode. It ensures proper operation and Protection for any shared resource.
3. True. An interrupt vector is the memory locationof an interrupt handler,which prioritizes interrupts and saves them in a queue if more than one interrupt is waiting to be handled.
4. True. DMA is a method that allows an I/O device to send or receive data directly to or fron the main memory,bypassing the CPU to speed up memory operations. The process is managed by a chip known as DMAC(DMA Controller).
5. True.The entire task can be blocked if a thread makes a blockng call. can be blocked if a thread makes a blocking system call.
6. True. Every memory access made by a user process is checked against these two registers, and if a memory access is attempted outside the valid range, then a fatal error is generated.
7. True. It uses layered approach.
8. True. Semaphores can lead to race conditions and do not protect against deadlocks. A monitor is a self-contained data structure wich contains atomic operations,condition variables and shared data. Can be used to solve a synchronizatio problem, because the shared data can only be accessed by the procedurs in the monitor ans the process can control the sequence in which the procedure access the shared data, therby enfrcing synchronization.
9. True. The long term scheduler selects which process has to be brought into ready queue, thus controls the degree of multi programming .
10. False. The thread scheduler is responsible for making sure that each thread has its own set f register vaues(stored in the TLB). A TLB is not shared between threads
11. False. Small time slice will sometimes improve the average response time of the system.
12. False.
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