1.5.3 File-System Management

 To make the computer system convenient for users, the operating system provides a uniform. logical view of information storage. The operating system abstracts from the physical properties of its storage devices to define a logical storage unit, the fil. The operating system maps files onto physical media and accesses these files via the storage devices.

File management it one of the most visible components of an operating system. Computers can store information on several different types of physical media. Secondary storage is the most common, but tertiary storage is also possible. Each of these media has its own characteristics and physical organization. Most are controlled by a device, such as a disk direve, that also has its own unique characteristics. These propertes include access speed, capacity, data-transfer rate, and access method (sequential or random).

A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data. Data files may be numeric, alphabetic, alphanumeric, or binary. File may be freeform(for example, text files), or they may be formatted rigidly (for example, fixed fields such as an mp3 music file). Clearly, the concept of a file is an extremely general one.

The operating system implements the abstract concept of a file by managing mass storage media and the devices that control them. In addition, files are normally organized into directories to make them easier to use. Finally, when multiple users have access to files, it may be desirable to control which user may access a file and how that user amy access if (for example, read, write, append).

The operating system is responsible for the following activities in connection with file management:

- Creating and deleting files

- Creating and deleting directories to organize files

- Supporting primitives for manaipulating files and directories

- mapping files onto mass storage

- Backing up files on stable (nonvolatile) storage media

File-management techniques are discussed in Chapter 13, Chapter 14, and Chapter 15.