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Sunday, April 28, 2013

What is fragmentation? What are different types of fragmentation?

In the field of computer science, the fragmentation is an important factor concerning the performance of the system. It has a great role to play in bringing the performance of the computers. 

What is Fragmentation?

- It can be defined as a phenomenon involving the inefficient use of the storage space that in turn reduces the capacity of the system and also brings down its performance.  
- This phenomenon leads to the wastage of the memory and the term itself means the ‘wasted space’.
- Fragmentation is of three different forms as mentioned below:
  1. The external fragmentation
  2. Internal fragmentation and
  3. Data fragmentation
- All these forms of fragmentation might be present in conjunction with each other or in isolation. 
- In some cases, the fragmentation might be accepted in exchange of simplicity and speed of the system. 

Basic principle behind the fragmentation concept. 
- The CPU allocates the memory in form of blocks or chunks whenever requested by some computer program. 
- When this program has finished executing, the allocated chunk can be returned back to the system memory. 
- The size of memory chunk required by every program varies.
- In its lifetime, a program may request any number of memory chunks and free them after use. 
- When a program begins with its execution, the memory areas that are free to allocated, are contiguous and long. 
- After prolonged usage, these contiguous memory locations get fragmented in to smaller parts. 
- Later, a stage comes when it becomes almost impossible to serve the large memory demands of the program. 

Types of Fragmentation

1.External Fragmentation: 
- This type of fragmentation occurs when the available memory is divided in to smaller blocks and then interspersed. 
- Certain memory allocation algorithms have a minus point that they are at times unable to order the memory used by the programs in such a way that its wastage is minimized. 
- This leads to an undesired situation where even though we have free memory, it cannot be used effectively since being divided in to very small parts that alone cannot satisfy the memory demands of the programs.  
- Since here, the unusable storage lies outside the allocated memory regions, this type of fragmentation is called external fragmentation. 
- This type of fragmentation is also very common in file systems since here many files with different sizes are created as well as deleted. 
- This has a worse effect if the file deleted was in many small pieces. 
- This is so because this leaves similar small free memory chunks which might be of no use.

2. Internal Fragmentation: 
- There are certain rules that govern the process of memory allocation. 
- This leads to the allocation of more computer memory what is required. 
- For example, as the rule memory that is allocated to programs should be divisible by 4, 8 or 16. So if some program actually requires 19 bytes, it gets 20 bytes. 
- This leads to the wastage of extra 1 byte of memory. 
- In this case, this memory becomes unusable and is contained in the allocated region itself and therefore this type of fragmentation is called as the internal fragmentation.
- In computer forensic investigation, the slack space is the most useful source for evidence. 
- However, it is often difficult to reclaim the internal fragmentation. 
- Making a change in the design is the most effective way for preventing it. 
Memory pools in dynamic memory allocation are the most effective methods for cutting down the internal fragmentation. 
- In this the space overhead is spread by a large number of objects.

3. Data Fragmentation: 
This occurs because of breaking up of the data in many pieces that lie far enough from each other.

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