What is spinlock, Peterson’s algorithm,Semaphore (programming),Dining philosophers problem, paging, etc





http://enos.itcollege.ee/~jpoial/docs/tutorial/essential/threads/deadlock.html starvation and deadlock




What is fragmentation? Different types of fragmentation? – Fragmentation occurs in a dynamic memory allocation system when many of the free blocks are too small to satisfy any request. External Fragmentation: External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous.Internal Fragmentation: Internal fragmentation is the space wasted inside of allocated memory blocks because of restriction on the allowed sizes of allocated blocks. Allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being used

What is a Safe State and what is its use in deadlock avoidance? – When a process requests an available resource, system must decide if immediate allocation leaves the system in a safe state. System is in safe state if there exists a safe sequence of all processes. Deadlock Avoidance: ensure that a system will never enter an unsafe state.

What is CPU Scheduler? – Selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them. CPU scheduling decisions may take place when a process: 1.Switches from running to waiting state. 2.Switches from running to ready state. 3.Switches from waiting to ready. 4.Terminates. Scheduling under 1 and 4 is non-preemptive. All other scheduling is preemptive.


When paging is used, a problem called “thrashing” can occur, in which the computer spends an unsuitable amount of time swapping pages to and from a backing store, hence slowing down useful work. Adding real memory is the simplest response, but improving application design, scheduling, and memory usage can help.

Journaling file system



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