Memory fragmentation by ofor williams daniel
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The document discusses memory fragmentation in computer systems, which occurs when allocated memory is divided into non-contiguous blocks, resulting in unusable free memory. It describes three types of fragmentation: internal, external, and data fragmentation, along with fixed and dynamic memory partitioning methods. Furthermore, it highlights the implications of fragmentation on system performance, including allocation failure and performance degradation, as well as techniques for addressing these issues.
Memory fragmentation by ofor williams daniel
- 1. (BSc. Computer Science) RIVERS STATE UNIVERSITY Port Harcourt
- 2. MEMORY FRAGMENTATION Memory fragmentation is when most of your memory is allocated in a large number of non- contiguous blocks, or chunks - leaving a good percentage of your total memory unallocated, but unusable.
- 3. 3 FORMS OF FRAGMENTATION 1. Internal Fragmentation 2. External Fragmentation 3. Data Fragmentation
- 4. INTERNAL FRAGMENTATION Due to the rules governing memory allocation, more computer memory is sometimes allocated than is needed.
- 5. EXTERNAL FRAGMENTATION External fragmentation arises when free memory is separated into small blocks and is interspersed by allocated memory.
- 6. DATA FRAGMENTATION Data fragmentation occurs when a collection of data in memory is broken up into many pieces that are not close together.
- 7. TWO MEMORY PARTITION TO ILLUSTRATE MEMORY FRAGMENTATION • FIXED PARTITION • DYNAMIC PARTITION
- 8. FIXED PARTITION In fixed partition, any program no matter how small occupies an entire partition. A program whose length is 4MB; yet occupies an 8MB partition when ever it is swapped in.
- 9. The use of unequal size partition to reduce (not eliminate) the amount of wasted space. HOW TO SOLVE THIS KIND OF FRAGMENTATION
- 10. O.S 8MB 8MB 8MB 8MB 8MB 8MB 8MB O.S 8MB 6MB 8MB 4MB 16MB 8MB 14MB Fig. 1.1 An illustration of two types of Fixed Memory Partition (a) Equal size Partition (b) Unequal size Partition
- 11. DYNAMIC FRAGMENTATION In dynamic partition, the partition are of various length and numbers. Processes are allocated exactly as much memory as it require or more. External fragmentation is caused by dynamic partition. The figure below will further explain the dynamic partition. How allocation of memory dynamically fragments the memory living smaller piece of memory that can’t be used or unusable.
- 12. Memory compaction is used to reduce (not eliminate) the amount of wasted space. HOW TO SOLVE THIS KIND OF FRAGMENTATION
- 13. Operating System 8MB Operating System 8MB Process 1 20MB Operating System 8MB Process 1 20MB Process 2 14MB 22MB Operating System 8MB Process 1 20MB Proces s 2 8MB Process 3 18MB Operating System 8MB Process 1 Process 3 Operating System 8MB Process 1 Process 2 Process 3 20MB 18MB 20MB 14MB 18MB Hole 1Hole 1Hole 1 Swapped 14MB 56MB 36MB (a) (b) (c) (f)(e)(d) Process 4 6MBHole 1 4MB4MB 4MB DYNAMIC FRAGMENTATION ILLUSTRATION
- 14. (f)(e) Operating System 8MB 20MB 8MB Process 3 18MB Process 4 6MBHole 2 Hole 1 Swapped Operating System 8MB 14MB 8MB Process 3 18MB Process 4 6MBHole 2 Hole 1 Fig. 1.2: Effect of dynamic partitioning 6MB 4MB 4MB Process 2 Hole 3 DYNAMIC FRAGMENTATION ILLUSTRATION (CONT.)
- 15. Process 2 in the ready suspended state is available. No sufficient memory for process 2 the OS swaps process 1 out (g). Process 2 is swap back in (h). Leaving another hole. The first three processes (b, c, d) are loaded in from the end of the OS leaving a hole at the end. At some point no process is ready. OS swaps out process 2 (e) leaving sufficient room for process 4 (f) Process 4 is smaller than process 2 therefore a hole is created. None of the process is in main memory is ready. THE FIG. 1.2 ABOVE IS AN ILLUSTRATION SHOWING THE EFFECTS OF DYNAMIC PARTITION USING A 64MB OF MAIN MEMORY. INITIALLY, MAIN MEMORY IS EMPTY EXCEPT FOR THE OPERATING SYSTEM THAT IS LOADED IN (A).
- 16. AN ILLUSTRATION OF FRAGMENTATION USING PLACEMENT ALGORITHM FIRST – FIT BEST – FIT NEXT - FIT
- 17. FIRST – FIT This algorithm begins to scan memory from the beginning and choose the first available block that is large enough to fit in a process or program. BEST – FIT This algorithm scans through the memory from the beginning to the end and choose the block that is closest in size to the request. NEXT – FIT This algorithm begins to scan the memory from the location of last placement and choose the next available block that is large enough. In satisfying a 16MB allocation request in fig. 1.3 First – fit scans the memory and fit in a 22MB space leaving a 6MB hole. Best – fit results in a 2MB fragment or hole in main memory. Next – fit result in a 20MB fragment in main memory. Fig. 1.3 (a) shows a number of placement and swapping out that has been done with fragments of different sizes. While fig. 1.3 (b) show first -, best -, and next – fit placements.
- 18. 8MB 12MB 22MB 18MB 8MB 6MB 14MB 36MB 8MB 12MB 6MB 2MB 8MB 6MB 14MB 20MB Fig. 1.3: An example of memory configuration before and after allocation of 16MB block. (a) After a number of placement and swapping out. (b) After a number of placement and swapping out. First - fit Best - fit Next - fit Allocated Block Possible New Allocation Free Block 16MB Block
- 19. MEMORY FRAGMENTATION PROBLEM 1. Allocation failure The most severe problem caused by fragmentation is causing a process or system to fail, due to premature resource exhaustion: if a contiguous allocation is needed and cannot be satisfied, failure occurs. 2. Performance degradation Fragmentation causes performance degradation for a number of reasons. Most basically, fragmentation increases the work required to allocate and access a resource. 3. Prematurely exhaustion of a cache, causing thrashing, due to cache holding block, not individual data. 4. Memory fragmentation may lead to complete loss of (application usable) free memory. 5. Memory fragmentation can lead to system crashes or other instability.
- 20. REFERENCES https://en.wiki/fragmentation_(computing) William Stalling, Operating System: Internal and Design Principle, Sixth Edition Published by Dorling Kinglersly, India 2009.