By Didar Hussain
Bacha Khan University Charsadda
This presentation will cover the idea of a file system. It contains much and more information i.e. different types of file systems like fat-16, fat-32, NTFS, Reiser file, journaling file, etc...
3. FILE CONCEPT
All computer applications need to store and retrieve information.
While a process is running, it can store a limited amount of
information within its own address space.
However, the storage capacity is too small for some applications
such that corporate record keeping etc.
Magnetic disks, optical disks and tapes are used for this long-term
storage, but they have much lower performance
By Didar Hussain
4. FILE CONCEPT
So to overcome these problems the concept of files are come.
Files are logical units of information created by processes.
A disk will usually contains thousands or even millions of them,
each one independent of the others.
Files are managed by the operating system.
How they are structured, named, accessed, used, protected, and
implemented.
By Didar Hussain
5. FAT-16, FAT-32 AND NTFS
All current operating systems allow strings of one to eight letters as
legal file names.
Frequently digits and special characters are also permitted like 2,
urgent!, and Fig.2-14 etc.
Many file systems support names as long as 255 characters.
UNIX falls in the first category; MS-DOS falls in the second.
UNIX was case sensitive while MS-DOS was not case sensitive.
By Didar Hussain
6. FAT-16, FAT-32 AND NTFS
In MS-DOS, for example, file names are 1 to 8 characters, plus an
optional extension of 1 to 3 characters.
In UNIX, the size of the extension, if any, is up to the user, and a file
may even have two or more extensions, as in homepage.html.zip
Windows 95 and Windows 98 both use the MS-DOS file system,
called FAT-16.
Windows 98 introduced some extensions to FAT-16, leading to FAT-
32, but these two are quite similar.
By Didar Hussain
7. FAT-16, FAT-32 AND NTFS
In addition, Windows NT, Windows 2000, Windows XP, and
Window Vista(WV) support both FAT file systems called NTFS.
So they have a native file system(NTFS) therefore also called NT
based operating system.
(NTFS) has different properties (such as file names in Unicode)
By Didar Hussain
8. REISER FILE SYSTEM
NTFS has an extensive journaling system and its structure is rarely
corrupted by system crashes.
It has been in development since its first release with Windows NT
in 1993.
The first Linux file system to do journaling was called ReiserFS, but
its popularity was impeded by the fact that it was incompatible with
the standard ext2 file system, ex2 compatible with ext3, which is
also a journaling but it was less ambitious project than ReiserFS.
So in simple words we can say the reiser file system was the first
file system which support the journaling file system at first time.
By Didar Hussain
9. JOURNALING FILE SYSTEM
The basic idea here is to keep a log of what the file system is going
to do before it does it, so that if the system crashes before it can do
its planned work, upon rebooting the system can look in the log to
see what was going on at the time of the crash and finish the job.
Such file systems, called journaling file systems, are actually in use.
Microsoft's NTFS file system and the Linux ext3 and ReiserFS file
systems use journaling
By Didar Hussain
11. FILE ACCESS
1. Sequence access
No jumping, will be access from start to end in a sequence
2. Random access
Processor rapidly can jump from one process to another
By Didar Hussain
12. FILE OPERATIONS
1. Create
The file is created with no data. The purpose of the call is to
announce that the file is coming and to set some of the attributes.
2. Delete
When the file is no longer needed, it has to be deleted to free up
disk space. There is always a system call for this purpose.
3. Open
Before using a file, a process must open it. The purpose of the
open call is to allow the system to fetch the attributes and list of
disk addresses into main memory for rapid access on later calls.
By Didar Hussain
13. FILE OPERATIONS
4. Close
When all the accesses are finished, the attributes and disk
addresses are no longer needed, so the file should be closed to
free up internal table space.
5. Read
Data are read from file.
6. Write
Data are written to the file again, usually at the current position.
7. Append
It can only add data to the end of the file.
By Didar Hussain
14. FILE OPERATIONS
8. Seek
For random access files, a method is needed to specify from
where to take the data. One common approach is a system call,
that repositions the file pointer to a specific place in the file.
After this call data can be read from, or written to, that position.
9. Get attributes
Processes often need to read file attributes to do their work.
10. Set attributes
Some of the attributes are user settable and can be changed after
the file has been created.
By Didar Hussain
15. FILE OPERATIONS
11. Rename
It frequently happens that a user needs to change the name of an
existing file.
By Didar Hussain