1. File Management
Organization of data
- Creating a file
- Storing a file in required directory
- Removing a file
- Opening a file
- Closing a file
- Maintaining of file details
- Name, Type, location, size ,
date and time of creation or modification
- File Protection
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2. File Attributes
- Name
- Type
- Location
- Size
- Protection
- Time, Date and User Identification
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3. File Attributes
Name
- Given by the user
- Only information that is kept in human readable form
Type
- Information required by systems that support different
types
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4. File attributes
Location
- A pointer to a device and to the
location of the file on that device
Size
- Current size of file (in bytes or words )
- Max size allowed
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5. File Attributes
Protection
- Access control information
( read, write and execute privileges )
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6. File Attributes
Time, date and user identification
- Creation
- Last modification
- Last use
(Useful for protection, security and usage monitoring )
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7. Basic File Operations ( Minimal Set )
1. Creating a file
2. Repositioning within a file
3. Deleting a file
4. Truncating a file
5. Reading a file
6. Writing a file
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8. Basic File Operations
1. Creating a file
• Allocation of space for the file in the file system
• Making an entry for the new file in the directory
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9. Basic File Operations
2. Writing a file
• Use a system call specifying
- Name of the file
- Information to be written
• Search directory for the associated entry
• Keep a write pointer
• Update write pointer after every write
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10. Basic File Operations
3. Reading a file
• Use a system call specifying
- Name of the file
- Address where to put the contents read
• Search directory for the associated entry
• Keep a read pointer
• Update read pointer after every read
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11. Basic File Operations
4. Repositioning within a file
• Also known as file seek operation
• Search directory for the appropriate entry
• Set current-file-position to a given value
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12. Basic File Operations
5.Deleting a file
• Search the directory for the named file
• Release all file space
• Erase the directory entry
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13. Basic File Operations
6. Truncating a file
• File contents erased
• Name and attributes of file unchanged
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14. Other File Operations
• Appending
• Renaming
Appending
Add some information at the end of the file
Renaming
Name of file changed
All other attributes unchanged
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15. Basic file operations can be combined to implement other
operations
Ex : Creating a copy of a file
- Create a new file
- Read from old file
- Write to new file
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16. Other Desirable Operations
Allow the user to get and set the various attributes of a file
Ex : i) get the file length
ii) set file attributes like file’s owner
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17. Other Desirable Operations
Most file operations involve searching the directory for the
entry associated with the named file
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18. To Avoid Constant Searching
• Many systems open a file when file first is used
• The operating system keeps a small table called the
Open file table
• Open file table contains information about open files
• When a file operation is requested, an index into the
open file table is used
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19. Other File Operations
When a file is no longer actively used, it is closed by
the process and the O.S. removes its entry in the Open
file table
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20. Other File Operations
• Some systems implicitly open a file when it is first referenced
• Close it automatically when the program that opened the file
terminates
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21. Other File Operations
Most systems require that a file be opened explicitly by the
programmer with a system call ( open ) before that file can be
used
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22. File Type Usual extension Function
Executable Exe, com, bin or none Ready to run machine
language program
Object obj, o Compiled, machine language,
not linked
Source code c, p, pas, f77, asm, a Source code in various
languages
Batch bat, sh Commands to the command
interpreter
Text txt, doc textual data,documents
Word Wp, tex, rrf etc Various word processor
Processor formats
Library Lib, a Libraries of routines
Print or view ps, dvi, gif ASCII or binary file in a
format for printing or viewing
Archive arc, zip, tar Related group of files for
archiving or storage
Fig : Common File Types
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23. File Type
One major consideration in designing a file system, and the
entire operating system, is whether the operating system
should recognize and support file types
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24. File Type
• If the operating system recognizes the type of a file
• it can then operate on the file in reasonable ways
• Ex : An attempt to print a binary-object form of a
program file can be prevented
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25. File Type
To implement file types, include the type as part of
the file name
For Ex : letters , documents
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26. File Type
The file name is split into two parts
- a name
- an extension
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27. File Type
• The file name is usually separated from the
extension by a period ( dot ) character
Ex : paycalc. cpp
• The name can consists up to 8 characters followed
by a period
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28. File Type
The extension tells what the file type is
• Extension can be up to 3 characters
• System uses the extension to indicate the type of the
file
• Type of operations that can be done on that file
For ex : .com , .exe & .bat extension are executable
file
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29. Summary
In this class, you have learnt
- file concept
- Understand file operations
- Know various file types
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