Page 23 - DCAP403_Operating System

Operating System

Notes There are few alternatives. Magnetic tape systems are generally too slow. In addition, they are
limited to sequential access. Thus tapes are more suited for storing infrequently used fi les, where
speed is not a primary concern.
The operating system is responsible for the following activities in connection with disk
management:
1. Free space management
2. Storage allocation
3. Disk scheduling.

I/O Management

One of the purposes of an operating system is to hide the peculiarities or specifi c hardware
devices from the user. For example, in UNIX, the peculiarities of I/O devices are hidden from the
bulk of the operating system itself by the I/O system. The operating system is responsible for the
following activities in connection to I/O management:
1. A buffer caching system
2. To activate a general device driver code

3. To run the driver software for specific hardware devices as and when required.

File Management

File management is one of the most visible services of an operating system. Computers can store
information in several different physical forms: magnetic tape, disk, and drum are the most
common forms. Each of these devices has it own characteristics and physical organisation.
For convenient use of the computer system, 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 file. Files are mapped, by the operating system, onto
physical devices.

A file is a collection of related information defined by its creator. Commonly, fi les represent

programs (both source and object forms) and data. Data files may be numeric, alphabetic or

alphanumeric. Files may be free-form, such as text files, or may be rigidly formatted. In general
a fi les is a sequence of bits, bytes, lines or records whose meaning is defi ned by its creator and
user. It is a very general concept.
The operating system implements the abstract concept of the file by managing mass storage

device, such as types and disks. Also files are normally organised into directories to ease their

use. Finally, when multiple users have access to files, it may be desirable to control by whom and

in what ways files may be accessed.
The operating system is responsible for the following activities in connection to the fi le
management:
1. The creation and deletion of fi les.
2. The creation and deletion of directory.

3. The support of primitives for manipulating files and directories.

4. The mapping of files onto disk storage.
5. Backup of files on stable (non volatile) storage.

6. Protection and security of the fi les.

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