assignment topic@2017-20 latehar gp

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Compaction in OS

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                    Compaction Compaction is a process in which the free space is collected in a large memory chunk to make some space available for processes. - In memory management, swapping creates multiple fragments in the memory because of the processes moving in and out. - Compaction refers to combining all the empty spaces together and processes. - Compaction helps to solve the problem of fragmentation, but it requires too much of CPU time. - It moves all the occupied areas of store to one end and leaves one large free space for incoming jobs, instead of numerous small ones. - In compaction, the system also maintains relocation information and it must be performed on each new allocation of job to the memory or completion of job from memory. - compaction is used  to minimize the probability of external fragmentation. In compaction, all the free partitions are made contiguous and all the loaded partitions are brought toget...
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Paging in OS

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                      Paging  Paging is a fixed size partitioning scheme. In paging, secondary memory and main memory are divided into equal fixed size partitions. The partitions of secondary memory are called as  pages . The partitions of main memory are called as  frames . Each process is divided into parts where size of each part is same as page size. The size of the last part may be less than the page size. The pages of process are stored in the frames of main memory depending upon their availability. Different operating system defines different frame sizes. The sizes of each frame must be equal. Considering the fact that the pages are mapped to the frames in Paging, page size needs to be as same as frame size. Example- Consider a process is divided into 4 pages P 0 , P 1 , P 2  and P 3 . Depending upon the availability, these pages may be stored in the main memory fra...
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Concept of segmentation in OS

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                 Segmentation :- A process is divided into Segments. The chunks that a program is divided into which are not necessarily all of the same sizes are called segments. Segmentation gives user’s view of the process which paging does not give. Here the user’s view is mapped to physical memory. There are types of segmentation: virtual memory segmentation  process is divided into a number of segments, not all of which are resident at any one point in time. 2 .Simple segmentation  – Each process is divided into a number of segments, all of which are loaded into memory at  run time, though not necessarily contiguously. There is no simple relationship between logical addresses and physical addresses in segmentation. A table stores the information about all such segments and is called Segment Table. Segment Table –  It maps two-dimensional Logical address into one-dimensional Physical address...
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