What are the Allocation Methods of a Disk Space?

Disk space allocation methods are techniques used by operating systems to manage and allocate disk space to files and directories. There are three main methods:

1. Contiguous Allocation: In this method, each file occupies a contiguous address space on disk. The directory contains the address of the block and the number of blocks needed by a file. This method is simple and provides good performance for sequential access. However, it suffers from external fragmentation and it's difficult to estimate the file size at the time of creation.

2. Linked Allocation: In this method, each file is a linked list of disk blocks. The directory contains a pointer to the first and last blocks of the file. To access a file, we start at the beginning and follow the pointers until we reach the desired block. This method eliminates external fragmentation and allows files to expand easily. However, it's inefficient for sequential access because disk blocks may be scattered all over the disk.

3. Indexed Allocation: In this method, each file has its own index block which stores the addresses of the file's blocks. The directory contains the address of the index block. This method eliminates external fragmentation and supports direct access. However, the index block can become a bottleneck if it's too small to hold all the pointers.

Each of these methods has its own advantages and disadvantages, and the choice of method depends on the specific requirements of the operating system and the applications running on it.