MEMORY MANAGEMENT
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Operating System - Memory Management Part 2 - Notes, Study notes of Operating Systems
In this document topics covered which are Fixed and Variable Partition , Fragmentation, Types of Fragmentation, Solution for Fragmentation, Free Frames, Paging Example .
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2010/2011
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MEMORY MANAGEMENT
Fixed and Variable Partition
- (^) Fixed Partition : Memory is divided into chunks. For example, 4K/8K/16K Bytes. All of these are same size.
- (^) Allocation : If a certain chunk can hold the program/data, then the allocation. If a chunk can not hold program/data then multiple chunks are allocated to accommodate the program/data.
Fragmentation
- (^) Fixed Size: Internal Fragmentation
- (^) Variable Size: External Fragmentation
Types of Fragmentation
- (^) External Fragmentation – total memory space exists to satisfy a request, but it is not in sequence.
- (^) Internal Fragmentation – allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being used
Solution for Fragmentation
- (^) Internal Fragmentation may be solved by using fixed size paging approach.
Solution for Fragmentation
- (^) External Fragmentation may be solved by using variable size segmentation approach.
Paging
- (^) Divide logical memory into blocks of same size called pages.
- (^) Keep track of all free frames
- (^) To run a program of size n pages, need to find n free frames and load program
- (^) Set up a page table to translate logical to physical addresses
- (^) Internal fragmentation
Paging Example
Free Frames
Before allocation (^) After allocation
Segmentation
- (^) Memory-management scheme that supports user view of memory
- (^) A program is a collection of segments. A segment is a logical unit such as: main program, procedure, function, method, object, local variables, global variables, common block, stack, symbol table, arrays
Logical View of Segmentation
1 3 2 4 1 4 2 3 user space physical memory space
Segmentation Architecture
(Cont.)
- (^) Relocation.
- (^) dynamic
- (^) by segment table
- (^) Sharing.
- (^) shared segments
- (^) same segment number
- (^) Allocation.
- (^) first fit/best fit
- (^) external fragmentation