File System Structure

File System Structure

• File system is mounted and maintain by the secondary storage which provides by disk. Characteristics of disk are as follows:

1. Same place is used for reading, writing and modification.

2. User can access disk directly for any block of information.

• Block is used for data transfer. Each block contains one or more sectors. The I/O transfer between memory and disk are performed on block. Default sector size is 512 bytes.

• Concept of file system is used for the efficient and convenient access to the disk. File system allows data to be stored, located and retrieved easily. The file system is generally composed of many different levels.

• Fig. 6.7.1 shows layers of file system.

• There are six layers. Each layers give support to neighbour layers. It also provides function to above layer and below layer. Each layer uses the features of neighbour layer while creating new features for use by the higher levels.

• File system creates two main design problems:

1. Creation of algorithm and data structure for of mapping of logical file system to physical secondary storage devices.

2. File system view for user.

• Input-output control interface: It consists of device driver and interrupt handler. Both are used for data transfer between main memory and disk system. Device driver used as a translator. Device driver input is high level commands and output is l ow level hardware specific instructions.

• Basic file system layer: It generates the command for device drivers. Particular device driver read data and writes physical blocks on the disk. Basic file system also manages the memory buffer and caches that hold various file system. Cache T memory is used to hold meta-data information of file system.

• File organization modules layer: This layer maintain information about files and be their logical blocks and physical blocks. It translate the logical block address to physical block address by considering physical location of files and file allocation method. File logical numbers are do not match with physical block containing data, so translation is required. Free space manager is included in file organization modules.

• Logical file system layer: It manages metadata information. Actual data is not part of metadata information. But file system structure is part of metadata. Directory structure is used to organized file module. Operating system maintains file control block for each file. UNIX uses inode instead of file control block. File control block stored information about file, location, ownership and access permissions.

• Application program layer: User/programmer creates an application programs.

• Physical hardware devices layer: It contains actual hardware device link disk, memory etc.

• Following is the list of different operating systems file system:

Google uses its own Google file system.