Wednesday, 23 January 2013
Support your answer with solid reasons for each of the two cases.
A concise, coherent and to the point answer is preferred over lengthy comments having irrelevant details. Comments, posted on regular Lesson's MDB or sent through email will NOT be considered in any case. Any request about such an acceptance will not be catered.
Solution:
When a computer program requests blocks of memory from the computer system, the blocks are allocated in chunks. When the computer program is finished with a chunk, it can free the chunk back to the computer. The size and the amount of time a chunk is held by a program varies. During its lifespan, a computer program can request and free many chunks of memory.
When a program is started, the free memory areas are long and contiguous. Over time and with use, the long contiguous regions become fragmented into smaller and smaller contiguous areas. Eventually, it may become impossible for the program to request large chunks of memory.
[edit]Types of fragmentation
Internal fragmentation
Due to the rules governing memory allocation, more computer memory is sometimes allocated than is needed. For example, memory can only be provided to programs in chunks divisible by 4, 8 or 16, and as a result if a program requests perhaps 23 bytes, it will actually get a chunk of 24. When this happens, the excess memory goes to waste. In this scenario, the unusable memory is contained within an allocated region, and is thus termed internal fragmentation.[1][2] Slack space is a very important source of evidence in computer forensic investigation.[3][4]
Unlike other types of fragmentation, internal fragmentation is difficult to reclaim; usually the best way to remove it is with a design change. For example, in dynamic memory allocation, memory pools drastically cut internal fragmentation by spreading the space overhead over a larger number of objects.
External fragmentation
External fragmentation arises when free memory is separated into small blocks and is interspersed by allocated memory. It is a weakness of certain storage allocation algorithms, when they fail to order memory used by programs efficiently. The result is that, although free storage is available, it is effectively unusable because it is divided into pieces that are too small individually to satisfy the demands of the application. The term "external" refers to the fact that the unusable storage is outside the allocated regions.
For example, consider a situation wherein a program allocates 3 continuous blocks of memory and then frees the middle block. The memory allocator can use this free block of memory for future allocations. However, it cannot use this block if the memory to be allocated is larger in size than this free block.
External fragmentation also occurs in file systems as many files of different sizes are created, change size, and are deleted. The effect is even worse if a file which is divided into many small pieces is deleted, because this leaves similarly small regions of free spaces.
A concise, coherent and to the point answer is preferred over lengthy comments having irrelevant details. Comments, posted on regular Lesson's MDB or sent through email will NOT be considered in any case. Any request about such an acceptance will not be catered.
Solution:
When a computer program requests blocks of memory from the computer system, the blocks are allocated in chunks. When the computer program is finished with a chunk, it can free the chunk back to the computer. The size and the amount of time a chunk is held by a program varies. During its lifespan, a computer program can request and free many chunks of memory.
When a program is started, the free memory areas are long and contiguous. Over time and with use, the long contiguous regions become fragmented into smaller and smaller contiguous areas. Eventually, it may become impossible for the program to request large chunks of memory.
[edit]Types of fragmentation
Internal fragmentation
Due to the rules governing memory allocation, more computer memory is sometimes allocated than is needed. For example, memory can only be provided to programs in chunks divisible by 4, 8 or 16, and as a result if a program requests perhaps 23 bytes, it will actually get a chunk of 24. When this happens, the excess memory goes to waste. In this scenario, the unusable memory is contained within an allocated region, and is thus termed internal fragmentation.[1][2] Slack space is a very important source of evidence in computer forensic investigation.[3][4]
Unlike other types of fragmentation, internal fragmentation is difficult to reclaim; usually the best way to remove it is with a design change. For example, in dynamic memory allocation, memory pools drastically cut internal fragmentation by spreading the space overhead over a larger number of objects.
External fragmentation
External fragmentation arises when free memory is separated into small blocks and is interspersed by allocated memory. It is a weakness of certain storage allocation algorithms, when they fail to order memory used by programs efficiently. The result is that, although free storage is available, it is effectively unusable because it is divided into pieces that are too small individually to satisfy the demands of the application. The term "external" refers to the fact that the unusable storage is outside the allocated regions.
For example, consider a situation wherein a program allocates 3 continuous blocks of memory and then frees the middle block. The memory allocator can use this free block of memory for future allocations. However, it cannot use this block if the memory to be allocated is larger in size than this free block.
External fragmentation also occurs in file systems as many files of different sizes are created, change size, and are deleted. The effect is even worse if a file which is divided into many small pieces is deleted, because this leaves similarly small regions of free spaces.
