TUGASAN 3:FILE MANAGEMENT

File storage management

A file management system is that set of system software that provides

services to users and applications related to the use of files. Typically, the only

way that a user or application may access files is through the file management

system. This relieves the user or programmer of the necessity of developing

special purpose software for each application and provide the system with a

means of controlling its most important asset.[GROS86] suggests the following

objectives for file management system:

•    To meet the data-management needs and requirements of the user, which

include storage of data and the ability to perform the operations listed

earlier

•    To guarantee, the extent possible that the data in the file are valid.

•    To optimize performance both from the system point of view in terms of overall throughput and from the user’s point of view in terms of response time

•    To provide I/O support for a variety of types of storage device

•    To minimize or eliminate the potential for lost or destroyed data

•    To provide a standardized set of I/O interface routines

•    To provide I/O support for multiple users in the case of multiple–user

Systems.

CONCEPT AND DESIGN

Computer can store information on several different storage media such as

magnetic disks, magnetic tapes and optical disks. So that the computer systems

will be convenient to use, the operating system provides a uniform logical view

of information storage. The operating system abstract from the physical

properties of its storage devices to define a logical storage unit, the file. File are

mapped, by the operating system, on to physical devices. This storage device are

usually non volatile, so the contents are persistent thru power failures and

systems reboots.

FILE DIRECTORY

a)      single directory

The simplest directory structure is the single-level directory. All files are

contained in the same directory, which is easy to support and understand. A

single level directory has significant limitation, however, when the number of

the file increases or when there is more than one user. Since all files are in the

same directory, they must have unique names. If we have two users who call

their data file test, then the unique name rule is violated.

b)two level directory

The major disadvantage to a single level directory is the confusion of files

names between different users. The standard solution is to create a separate

directory for each user.

In the two level directory structures, each user has her own user file

directory (UFD). Each UFD has a similar structure, but lists only the files of a

single user. When a user job starts or a user log in, the system master file

directory (MFD), is search. The master file directory is index by user name or

account number, and each entry point to the UFD for that user. When a user

refers to a particular file, only his own UFD is search. Thus different users may

have files with the same name, as long as all the file names within it UFD are

unique.

c) multilevel directory

Once we have seen how to view a two level directory as two-level tree, the

natural generalization is to extend the directory structure to a tree of a arbitrary

Masterheight. This generalization allows users to create their own subdirectories and to

organize their files accordingly. The MS-DOS system for instance is structured

as a tree. In fact a tree is the most common directory structure. The tree has a

root directory. Every files in the system has a unique path name. A path name is

the path from the root through all the sub directories to a specified file.

 Linking Block

FILE MAP

BLOCK INDEX