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Paging and Segmentation
The document discusses memory segmentation and paging techniques used in operating systems. Segmentation divides memory into variable-length segments, while paging divides memory into fixed-size pages. Paging maps logical pages to physical frame addresses using a page table for efficient memory access. It allows programs to access more memory than is physically available by swapping pages between memory and disk. The combination of segmentation and paging provides memory protection and reduces internal and external fragmentation.
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Paging and Segmentation
- 1.Segmentation And PagingForHCTM Kaithal Presented By :Madhur Gupta1712159CSE A 5th Sem ( 2012-2016)
- 2.Contents InThe Presentation•Memory Segmentation• Segmentation Hardware• Advantages• Disadvantages• Paging• Frames• Mapping• Combining Segmentation with Paging
- 3.1. Physical Memory-Totalmemory of the computer. EX: RAM2. Logical Memory- CPU memory3. Virtual memory- An imaginary memory area supported by someoperating systems (for example, Windows). It is an extension of logicalmemory
- 4. If thesize of the program isgreater than the availablememory size, then the conceptof virtual memory is used Ever wondered how a 10GBGame like God OfWar fits intoyour 2GB RAM computer?
- 5. Paging isa memory management technique in which the memoryis divided into fixed size pages. Paging is used for faster access to data. It is a logical concept
- 6.STATEMENT 1STATEMENT 2STATEMENT3STATEMENT 4STATEMENT 5STATEMENT 6STATEMENT 7Suppose a program X consists of 7statements. But the memory can hold only4 statements, then Paging concept is used.PROGRAM XSTATEMENT 1STATEMENT 2STATEMENT 3STATEMENT 4STATEMENT 5STATEMENT 6STATEMENT 7
- 7. Frames arephysical concept It is present in the RAM We cannot see Pages, but we can see Frames
- 8. Converting pages(virtualaddress) into frames (physical address) Enables program to be executed It is performed by the Memory Management Unit (M.M.U.)CPU(WHEREPAGESAREDIVIDED)MMUMemory 1 Memory 2Virtual address ofeach pageConverts virtualaddress tophysical address If any error error occurs at anyphysical address, it is quicklyretrieved from memory andsent to the CPU
- 9.0 0 00 0 1 0 1 1 1 0 1 1 1 06-bit page # 10-bit offset #16-bit logical address0 0 0 0 1 0 11 0 0 0 1 1 00 0 0 1 1 0 0 1 1 1 0 1 1 1 1 0PageTable16-bit Physical address
- 10. LOGICAL ADDRESSPAGENUMBER(WHICH PAGE ISTO BESEARCHED INTHEMEMORY)PAGE OFFSET(WHICH BYTE OF DATA ISTOBE READ FROMTHAT PAGE)MAXIMUM OF 6 BYTES MAXIMUM OF 10 BYTES PHYSICAL ADDRESSFRAME NUMBER FRAME OFFSETMAXIMUM OF 6 BYTES MAXIMUM OF 10 BYTES
- 11.
- 12.pageframe 0pageframe 1pageframe2pageframe 3physical memoryoffsetphysical addressF3’s ValueF3F2F0page table(MMU)offsetlogical addressP=3CPUP0P1P2P3P4P5P6P7F1
- 13.The paging processis protected by the concept ofinsertion of an additional bit calledVALID/INVALID BITConsider a 14 bit address space= 2^14=16383 bytesLet us set an address limit of 10468If five process are defined within this address space(P0-P4), it is considered as aValid bitProcess P5 has started before 10468, so that alone isconsideredThe remaining processes are considered as InvalidIn this way the pages are internally fragmentedThis is how Paging is protected
- 14.• No externalFragmentation•Simple memorymanagementalgorithm• Swapping is easy(Equal sized Pagesand Page Frames)• Internalfragmentation• Page tables mayconsume morememory.
- 15. Segmentation isone of the most common ways to achieve memory protection. Because internal fragmentation of pages takes place, the user’s view ofmemory is lost The user will view the memory as a combination of segments In this type, memory addresses used are not contiguous Each memory segment is associated with a specific length and a set ofpermissions. When a process tries to access the memory it is first checked to see whether ithas the required permission to access the particular memory segment andwhether it is within the length specified by that particular memory segment.
- 16.13241423user space physicalmemory spaceFreeFree
- 17. Segment table- maps two-dimensional user defined address into one-dimensional physical address base - starting physical address of the segment limit - length of segmentLogical Address spaceSegment numberOffsetThe maximum length of the offset value is 12 bits
- 18.
- 19. No internalfragmentation Segment tables consume lessmemory than page Lends itself to sharing dataamong processes. Lends itself to protection.Costly memory managementalgorithmAs processes are loaded andremoved from memory , thefree memory space is brokeninto little pieces ,causingexternal fragmentation
- 21.In a combinedpaging/segmentationsystema user’s addressspace is broken up into anumber of segments.Each segment is brokenup into a number of fixed-sized pages which areequal in length to a mainmemory frameSegmentation is visible tothe programmerPaging is transparent tothe programmer
- 22.• www.cs.mun.ca/~paul/cs3725/material/web/notes/node12.html• http://en.wikipedia.org/wiki/Memory_segmentation•http://www.gitam.edu/eresource/comp/gvr(os)/8.5.htm• http://www.cs.columbia.edu/~junfeng/13fa-w4118/lectures/l05-mem.pdf• http://www.openclarity.com/node/22• http://www.cs.columbia.edu/~junfeng/12sp-w4118/lectures/l05-mem.pdf