STORAGE MANAGEMENT AND PAGING ALGORITHMS.pptx
- 1. Unit II - Storage management
- 2. Logical Address is generated by CPU while a program is running. The logical address is virtual address as it does not exist physically, therefore, it is also known as Virtual Address. This address is used as a reference to access the physical memory location by CPU. The term Logical Address Space is used for the set of all logical addresses generated by a program’s perspective. The hardware device called Memory-Management Unit is used for mapping logical address to its corresponding physical address.
- 4. Differ in execution time
- 5. It identifies a physical location of required data in a memory. The user never directly deals with the physical address but can access by its corresponding logical address. The program needs physical memory for its execution, therefore, the logical address must be mapped to the physical address by MMU before they are used.
- 8. Parameter LOGICAL ADDRESS PHYSICAL ADDRESS Basic generated by CPU location in a memory unit Visibility User can view the logical address of a program. User can never view physical address of program. Generation generated by the CPU Computed by MMU Access The user can use the logical address to access the physical address. The user can indirectly access physical address but not directly. Editable Logical address can be change. Physical address will not change. Also called virtual address. real address.
- 9. Swapping is a memory management scheme in which any process can be temporarily swapped from main memory to secondary memory so that the main memory can be made available for other processes. It is used to improve main memory utilization. In secondary memory, the place where the swapped-out process is stored is called swap space.
- 10. It is the type of memory allocation method. When a process requests the memory, a single contiguous section of memory blocks is allotted depending on its requirements.
- 11. Fixed-size Partition Scheme In this type of contiguous memory allocation technique, each process is allotted a fixed size continuous block in the main memory. This technique is also called static partitioning.
- 13. Variable-size Partition In this type of contiguous memory allocation technique, no fixed blocks or partitions are made in the memory.
- 15. In Operating Systems, Paging is a storage mechanism used to retrieve processes from the secondary storage into the main memory in the form of pages. The main idea behind the paging is to divide each process in the form of pages. The main memory will also be divided in the form of frames. One page of the process is to be stored in one of the frames of the memory.
- 16. The partitions of secondary memory are called as pages. The partitions of main memory are called as frames.
- 19. Address generated by CPU is divided into: ◦ Page number (p) - used as an index into a page table which contains base address of each page in physical memory. ◦ Page offset (d) - combined with base address to define the physical memory address that is sent to the memory unit. It refers to the number of bits necessary to represent a certain word on a page, For ex: 10 bits
- 21. Segmentation method works almost similarly to paging, only difference between the two is that segments are of variable-length whereas, in the paging method, pages are always of fixed size.
- 22. Segment table contains mainly two information about segment: Base: It is the base address of the segment Limit: It is the length of the segment.
- 23. Example of Segmentation in OS Consider that a user program has been divided into five segments and they are numbered from segment 0 to segment 4, as you can see them in the logical address space. You also have a segment table which has entries for these segment with their base address in physical memory and their limit.
- 25. Virtual memory is a memory management technique where secondary memory can be used as if it were a part of the main memory.
- 27. Demand paging is a memory management scheme employed by modern operating systems to manage physical memory resources.
- 28. Demand paging is a process in which data is moved from secondary memory to RAM on a demand basis, which means all data is not stored in the main memory because the space is limited in RAM.
- 29. Demand Paging is a method in which a page is only brought into main memory when the CPU requests it.
- 32. In an operating system that uses paging for memory management, a page replacement algorithm is needed to decide which page needs to be replaced when a new page comes in. FIFO LRU OPTIMAL
- 33. Page Replacement Algorithms: Page fault/ Miss: If the searching page is not in memory Page Hit: If the searching page that was available in memory.
- 34. This is the simplest page replacement algorithm. Replaced the pages that has been in memory for the longest time
- 35. Example 1: Consider page reference string 1, 3, 0, 3, 5, 6, 3 with 3 page frames. Find the number of page faults.
- 36. Advantages This algorithm is simple and easy to use. FIFO does not cause more overhead. Disadvantages This algorithm does not make the use of the frequency of last used time rather it just replaces the Oldest Page. There is an increase in page faults as page frames increases. The performance of this algorithm is the worst.
- 37. In this algorithm, pages are replaced which would not be used for the longest duration of time in the future Advantages of OPR This algorithm is easy to use. This algorithm provides excellent efficiency and is less complex. For the best result, the implementation of data structures is very easy Disadvantages of OPR Practical Implementation is not possible because the operating system is unable to track the future request
- 38. Example-2: Consider the page references 7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 3 with 4 page frame. Find number of page fault.
- 39. In this algorithm, page will be replaced which is least recently(Long back) used. The page that has not been used for the longest time in the main memory will be selected for replacement. This algorithm is easy to implement.
- 40. Example-3: Consider the page reference string 7, 0, 1, 2, 0, 3, 0, 4, 2, 3, 0, 3, 2, 3 with 4 page frames. Find number of page faults.
- 41. Advantages of LRU It is an efficient technique. With this algorithm, it becomes easy to identify the faulty pages that are not needed for a long time. It helps in Full analysis. Disadvantages of LRU It is expensive and has more complexity. There is a need for an additional data structure.
- 42. In this algorithm, page will be replaced which has been used recently. This is the Last in First Out algorithm and works on LIFO principles. In this algorithm, the newest page is replaced by the requested page.
- 43. Example: Let’s see how the LIFO performs for our example string of 3, 1, 2, 1, 6, 5, 1, 3 with 3-page frames:
- 44. Advantages Simple implementation: Low overhead: Disadvantages Poor performance: May result in page thrashing: LIFO page replacement algorithm can result in a situation known as page thrashing, where the pages are frequently swapped in and out of memory, leading to high page fault rates and poor system performance.
- 48. THANK YOU