File System Storage

FILE SYSTEM STORAGE

1 File Concept

ü A file is a named collection of related information that is recorded on secondary storage.

ü From a user’s perspective, a file is the smallest allotment of logical secondary storage; that is, data cannot be written to secondary storage unless they are within a file.

   Examples of files:

   A text file is a sequence of characters organized into lines (and possibly pages).

   A source file is a sequence of subroutines and functions, each of which is further organized as declarations followed by executable statements. An object file is a sequence of bytes organized into blocks understandable by the system’s linker. An executable file is a series of code sections that the loader can bring into memory and execute.

2 File Attributes

            Name: The symbolic file name is the only information kept in human readable form.

            Identifier: This unique tag, usually a number identifies the file within the file system. It is the non-human readable name for the file.

            Type: This information is needed for those systems that support different types.

            Location: This information is a pointer to a device and to the location of the file on that device.

            Size: The current size of the file (in bytes, words or blocks)and possibly the maximum allowed size are included in this attribute.

            Protection: Access-control information determines who can do reading, writing, executing and so on.

            Time, date and user identification: This information may be kept for creation, last modification and last use. These data can be useful for protection, security and usage monitoring.

3 File Operations

v Creating a file

v Reading a file

v Repositioning within a file

v Deleting a file

v Truncating a file

4 File Types