Question

In order to allow fast accessing to the stored files on the disk, the space allocation these files is the crucial context.

Discuss the methods with diagram and descriptions as follows

c) Indexed allocation

Answer 1

Dear student, File allocation is good to know that how to store the files so that it is easy to retrieve fast and also utilize the memory. so that is all about your file allocation are given below-

File Allocation Methods-:

The methods which are used to allocate the file into disk to allow fast access on the disk. it is manner when we are storing the files on the disk.It is used to utilization of disk space and fast access of file blocks. There are Three types of File allocations on the disk-

FILE ALLOCATION METHOD INDEX ALLOCATION CONTIGUOUS ALLOCATION LINKED ALLOCATION

1. Contiguous Allocation
2. Linked Allocation
3. Indexed Allocation

• ​​​​​​​Contiguous Allocation-: in contiguous allocation Each file contains or allocate contiguous block which simply means that we have given a continue block of address. for example if we have a file name hello , length of the file is 4 block and starting address of the file if ADD so that their blocks will be as follows ADD,ADD+1,ADD+2,ADD+3. this is called contiguous allocation.

​​​​​​​Advantages-:

• It will be valid for Direct access and Sequncial access.
• It is faster access due to Contiguous block in disk.

Disadvantages-:

• sometimes for large files it is more problem with availability of contiguous space on the disk.
• In term of memory utilization it is not efficient so that it goes to internal and external fragmentation.

My book Hello -Mail lab length File My book hello mail lab

Contiguous Allocation

• Linked Allocation-: In linked file allocation, blocks are allocated in the disk at random not contiguous so that it is easy to store a large file into disk. As we know that linked list each block node contains the next block address of the block so that it is called indexed block.

Advantages and Disadvantages-:

• For large files it is easy to store in the block because it stores in random disk blocks.
• It is the good way to utilize memory in the disk.
• For random disk blocks, large file contains more blocks on the disk space so that it will slows down because of accessing every blocks at individual.
• Pointer is required to access the blocks of data so that they can access randomly.

​​​​​​​

end File name My book Start 15 15 Linked Allocation

• Indexed Allocation-: In this allocation, a block is used for storing all the pointer address of other block of the file known as Indexed Block. Inthis file access Each file has a single indexed block and store all the pointer of the block.

​​​​​​​Advantages -:

• It will give fast access for direct store blocks allocation.
• It removes the external fragmentation.
• It is more efficient to store the file blocks.

​​​​​​​Disadvantages-:

• For very large file it is very dificult to store indexed block for all the pointers of the file block.
• Wastage of memory in storing the pointer of blocks.
• It is not efficient for very small size files in term of memory utilization.

​​​​​​​

10 File name My Indexed block 14 Indexed Allocation

​​​​​​​For very large allocation of file it is not easy to store all the pointer address of all block to indexed block so for remove this problem we have to use these scheme for storing the pointer-:

1. Linked Scheme-: In this scheme, two or more indexed blocks are used to store the pointer and the these blocks are linked together to remove the problem.
2. Multilevel index-: In this, first level of indexed block is used to point to the second level of indexed block which is intend to the disk block of the file this may be differ according to  size of the file.
3. Combined Scheme-: In this scheme there is a special block which is called information block which contains the namre, length , authorith, direct blocks and indirect blocks. this is used to store the address of all disk block of the file so that it points to access the file.

So that we can store our files and retrieve with fast manner in the disk space. that's all about this.

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