Wednesday, September 20, 2017

What is a file system and an i-node?

File system is a method of storing and organising computer files and their data. It organises the files into a database for storage, organisation, manipulation and retrieval by the computers operating system.

I-node is a unique data structure that contains information about file. Each file has an associated i-node which is created at the time of creation of file. Each file has an i-node and is identified by an i-node number. I-nodes store information on files such as user, group, ownership access mode and type of file and the pointers to blocks of file etc.

User programs before execution, is brought into memory. Memory is partitioned and each partition contains a base address and a size. Base address is stored in a relocation register before execution of program of program and the size of program checked against the allowable size and addresses that are generated by the program are continuously monitored. This is done with the help of a limit register. If base address plus the address generated by the program exceed the limit register contents, then it result in trap being generated and further execution of the program is not allowed. Operating systems have other protection mechanisms also like access rights bits to implement read/write/execute accesses. Only owners of a file may be allowed to execute. If only owner allow others and group members, they can execute the files. This is done by setting access rights bits by owner of file.

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