what is contiguous storage allocation
Answers
In this scheme, a file is made from the contiguous set of blocks on the disk. Linear ordering on the disk is defined by the disk addresses. In this scheme only one job is accessing the disk block b after that it accesses the block b+1 and there are no head movements. When the movement of the head is needed the head moves only from one track to another track. So the disk number that is required for accessing the contiguous allocation is minimal. Contiguous allocation method provides a good performance that’s why it is used by the IBM VM/CMS operating system. For example, if a file requires n blocks and is given a block b as the starting location, then the blocks assigned to the file will be: b, b+1, b+2,..., b+n-1. This means that given the starting block address and the length of the file (in terms of blocks required), we can determine the blocks occupied by the file. For a contiguous allocation the directory entry the address of the starting block and Length of the allocated portion.
The file 'A' in the following figure starts from block 19 with length = 6 blocks. Therefore, it occupies 19, 20, 21, 22, 23, 24 blocks.
Each file in the disk occupies a contiguous address space on the disk.
In this scheme, the address is assigned in the linear fashion.
The is very easy to implement the contiguous allocation method.
In the contiguous allocation technique, external fragmentation is a major issue.
Advantages:
In the contiguous allocation, sequential and direct access both are supported.
For the direct access, the starting address of the kth block is given and further blocks are obtained by b+K,
This is very fast and the number of seeks is minimal in the contiguous allocation method.
Disadvantages:
Contiguous allocation method suffers internal as well as external fragmentation.
In terms of memory utilization, this method is inefficient.
It is difficult to increase the file size because it depends on the availability of contiguous memory.
Explanation:
Contiguous Memory Allocation : Contiguous memory allocation is basically a method in which a single contiguous section/part of memory is allocated to a process or file needing it. ... The main memory is a combination of two main portions- one for the operating system and other for the user