OS-Inode Pointer System

The idea of managing the allocation of disk space to a file by recording for each file, a list of the blocks allocated to the file. A file can range in size from zero bytes to several million bytes. In Unix, the inodes have a fixed size which accordingly can only accommodate a fixed number of pointer entries. The inode infact 13 pointers, the first ten of these are direct pointers is they each supply directly a physical address of a block of the file.
The other 3 pointers don’t point directly to data blocks but to index pointers, which themselves contain list of blocks on further index blocks.

For files greater than 10 blocks (ie size > 5120 is block size = 512) the eleventh pointer references a block of the file. If this is still insufficient the twelth pointer has to employed. This points to a block which contains a set of pointers, each of which points to another index block ultimately, but rarely the 13 pointer may be needed. 

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