File management in an operating system, and what is the file concept? FIle naming and file attributes. - Cyber security & Technology

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Tuesday, August 21, 2018

File management in an operating system, and what is the file concept? FIle naming and file attributes.



FILE MANAGEMENT 


·        File management is the process of storing, controlling and managing data stored on disks or secondary storage in the form of files.

·        File management ensures the consistency of data when multiple users access files concurrently.

·        File management also provides the measures for file security and protection. 




FILE CONCEPT


·        A file is a logical collection of information stored on secondary storage such as hard disk.

·        Physically, a file is the smallest allotment of secondary storage device e.g. disk. Logically, a file is a sequence of logical records ie. a sequence of bits and bytes.

·        Files can be used to contain data and programs (both source and object program).

·        Data files can be numeric, alphabetic, alphanumeric or binary.

·        A file has various attributes like name, type, location, size, protection, time and date of creation etc.

1.      File Naming

·        A file can be given a name for the convenience of its use by its creator.

·        A name is attached to every file so as to uniquely identify it and access it through its name.

·        The exact rules for naming file vary from system to system but all the operating systems allow string of one to eight letters as legal file name.

·        Digits and few special characters are also allowed in file names.

·        Some systems differentiate between uppercase and lower case characters in names, whereas other systems consider the two cases equivalent. For example, UNIX differentiate uppercase letters from the lowercase whereas MS-DOS does not.

·        Thus in UNIX, files-HELLO, hello, Hello and HEllo are different whereas in MS-DOS, they all represent same file.

2.      File attributes

·        File attributes are required by file management system to manage a file.

·        Few attributes are accessible for users, such as access privileges, name, or size of a file, whereas some of them are specifically assigned to file for file system usage .

·        File attributes vary from one operating system to other. The various file attributes are listed in fig. 9.1 No existing system has all of these, but each one is present in some system.

·        The first four attributes shown in table are related to file protection and tell who may access it and who may not.

·        The flags are bits or short fields that enable or control some specific property:

1.      Hidden flag.  Hidden files do not appear in the listing of a file.

2.      Archive flag. Archive flag bit keeps track of whether the file has been  backed up.

3.      Temporary flag. This flag allows a file to be marked for automatic deletion when the process that created it terminates.

·        The various times keep tract of when the file was created, most recently used and most recently modifies.

·        The current size attribute tells how big a file is at present.

·        The maximum size attribute tells the maximum amount of storage reserved for a file in advance. It is used for mainframe operating systems and not in minicomputers and personal computer systems.

SNO.
Field
Meaning
1
Protection
Who can access a file and in what way ( reading, writing, executing).
2
Password
Password needed to access a file.
3
Creator
ID of a person who created a file
4
Owner
Current owner of a file
5
Read – Only flag
Zero for read/write , 1 for read only
6
Hidden flag
Zero for normal , 1 for do not display in listings
7
System flag
0 for normal file, 1 for system file
8
Archive flag
0 has been backed up, 1 for needs to be backed up.
9
ASCII/Binary flag
0 for ASCII file , 1for binary file
10
Random access flag
0 for sequential access only, 1 for random access.
11
Temporary flag
0 for normal , 1 for delete on process exit.
12
Lock flag
0 for unlocked  , non zero for locked
13
Creation time
Date and time of file was created .
14
Time of last access
Date and time file was last accessed
15
Time of last change
Date and time file was last changed
16
Current size
Number of bytes in a file
17
Maximum size
Maximum size file may grow to


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