File systems are an integral part of all operating systems with long term storage capacity. There are two distinct parts of a file system, the mechanism for storing files and the directory structure in which they are organized. In modern operating systems where it is possible for many users to access the same file at the same time it has also become necessary for such features as access control and the various forms of file protection to be implemented.
A file is a set of binary data. A file may refer to a program, document, or in some cases a portion of the file system itself. In modern computer it is quite common for them to be several different storage devices connected to the same computer. A common data structure, such as a file system allows the computer to access many different storage devices in the same way, for example, when you look at the contents of a hard drive or on a CD is displayed using the same interface, even if they are completely different mediums with data mapped on them in completely different ways. Files can have very different data structures within them, but they can be achieved using the same methods embedded in the file system. The arrangement of data within the file is then decided by the creation program. The file system also stores a set of attributes to the files within it.
All files have names with which you can access by the user. In most modern file systems the name is composed of three parts, its unique name, a period and an extension. For example, the 'bob.jpg' file is uniquely identified by the first word 'bob', jpg extension indicates that it is a JPEG image file. The file extension allows the operating system to decide what to do with the file if someone tries to open it. The operating system maintains a list of file extension associations. If a user tries to access 'bob.jpg' then it would most likely be opened in any default image viewer's systems.
The system also stores the location of a file. In some file system files you can only be stored as a contiguous block. This simplifies storage and access to the files as the system then only needs to know where the file begins on the disk and how big. It does however lead to complications if the file is to be extended or removed as there may not be enough space to fit the larger version of the file. Most modern file systems overcome this problem by using linked file allocation. In this way the file to be stored in any number of segments. The file system must be sustained where each block of the file is and how large they are. This greatly simplifies file space allocation, but it is slower than contiguous allocation as it is possible that the file is scattered around the disk. Modern operating systems overome this defect by providing a disk defragmentation. It is a utility that rearranges all the files on the disk so that they are all in contiguous blocks.
information on file protection is also integrated into the file system. The protection can range from simple systems implemented in the first windows FAT system in which the files can be marked as read-only or hidden to most secure systems implemented in NTFS as the file system manager can set read and write separate the access rights for different users or groups of users. Although file protection adds a great deal of complexity and potential difficulties it is essential in an environment where most computers or other user can have access to the same unit through a network shared system or time as the Raptor.
Some file systems also store data about which user created a file and now have created. Although this is not essential for the operation of the file system it is useful to the system users.
In order for a file system to function properly they need a certain number of tasks defined for creating, opening and editing a file. Almost all file systems provide the same basic set of methods for manipulating files.
A file system must be able to create a file. To do this there must be enough disk space to accommodate the file. There must also be no other files in the directory that is to be positioned with the same name. Once you create the file, the system will make a record of all the attributes mentioned above.
Once the file has been created, we may need to edit it. This can be simply adding some data to the end of it or by removal or replacement of the data already stored within it. In doing so the system maintains a press in which the next write operation for the file must be write pointer.
In order for a file to be useful must of course be legible. To do this you must know the name and path of the file. From this the file system can ascertain where the file is stored on the drive. When reading a file, the system maintains a read pointer. This stores that part of the disk is to be read next.
In some cases it is not possible to simply read all the files in memory. The file system also allow you to reposition the read pointer within a file. To do this, the system needs to know which point the file you want the read pointer to jump. An example of how this would be useful is a database system. When a query is made on the database it is obviously inefficient to read the entire file to the point where the requested data is instead the application of database management could determine where in the file the desired data bits and jump to it. This file is often called seeking.
The file system also allow you to delete files. To do this you need to know the name and path of the file. To delete a file system simply removes the item from the directory structure and adds all the space that previously occupied the free space list (or any other operating system that uses free space).
These are the most basic operations required by a file system to function properly. They are present in all modern computer file systems, but the way in which they work may vary. For example, to perform the file delete operation in a modern file system such as NTFS that has the built-in file protection it would be more complicated than the same operation in an older file system such as fat. Both systems should first check if the file was in use before continuing, NTFS should therefore check whether the user is currently deleting the file you have permission to do so. Some file systems also allow more people to open the same file at the same time and decide if users are allowed to write a file back to disk if other users are currently open. If two users have read and write file should be allowed to overwrite a, while the other still open? Or, if a user has read-write permission and another only has read permission on a file if the user with write permission to be allowed to override if there is any possibility of another user even trying to do?
different file systems also support different access methods. The simplest method to access information in a file is sequential access. This is where the information in a file is accessible from the start one record at a time. To change the position in a file can be rewound or forwarded a number of records or reset at the beginning of the file. This method of access is based on file storage systems for tape drives, but it also runs on sequential access devices (like mordern DAT tape drives) as those of random access (like hard drives). Although this method is very simple in its operation and ideal for certain tasks such as media playback is very inefficient for more complex tasks, such as managing databases. A more modern approach, which facilitates a better reading of the tasks that are not likely to be sequential is direct access. Direct Access enables recordings to be read or written in any order on the application requires. This method of allowing any part of the file to be read in any order is more suitable for modern hard drives as too allow any part of the converter to be read in any order with little reduction in the transfer rate. The direct access is more suitable for the majority of applications of sequential access as it was designed around the support of most common in use today on the contrary of what storage is no longer used much except for large not in the back line -up. Given the way it works direct access it is also possible to build other access methods on top of direct access as the sequential access or the creation of an index of all records in the file for speeding speed up the data search in a file.
In addition to storing and managing files on a file system also maintains a directory system in which you reference files. Modern hard drives store hundreds of gigabytes. The file system helps to organize these data division into directory. A directory can contain files or more directories. As the files there are several basic operations that a file system must be in a position to execute its directory structure to function properly.
needs to be able to create a file. This is covered with a summary of peration of a file, but also creates the file must be added to the directory structure.
When a file is deleted, the space the file must be marked as free space. The file itself also needs to be removed from the directory tree.
The files may need to be renamed. This requires a modification of the directory structure, but the file itself remains non-changed.
LIST directory. To use the disc correctly the user needs to know what is in all the directories stored on it. On top of this, the user must be able to browse through the directories on your hard drive.
Since the first directory structures have been designed that have gone through several major evolutions. Before directory structures have been applied to systems to archive all the files were stored on the same level. This is basically a system with a directory where all the files are kept. The next advancement of this, which could be considered the first directory structure is the directory two levels. In this There is a singe directory listings that are all on the same level. The files are then stored in these directories. In this way, different users and store files across applications separately. After this came the first directory structures as we know them today, directory trees. directory tree structure improves on two-level directories, allowing directories and files to be stored in the directory. All modern file systems use tree structure of the directory, but many have additional features, such as security built on them.
Protection can be implemented in many ways. Some file systems allow you to have password protected directories. In this system. The file system does not allow you to access a directory before it is given a user name and password for it. Others extend this system as different users or groups access permissions. The operating system requires the user to sign in before using the computer and thus limit their access to areas that do not have permission for. The system used by the Department of Computer Science for the storage and presentation of courses Raptor is a good example of this. In a file system as NTFS all types of storage space, access to the network and the use of devices such as printers it can be controlled in this manner. Other types of access control can also be implemented outside of the file system. For example applications like winning zip allows you to password-protect files.
There are many different file systems currently available to us on many different platforms and based on the type of application and the size of the units several different file system suit situations. If you were to design a file system for a tape backup system, then a method of sequential access would be more suitable for a direct access method taking into account the constraints of hardware. Even if you have a small hard drive of a computer at home then there would be no real advantage to using a more complex system with features such as file protection as it is not likely to be necessary. If you were to design a file system for a round of 10 gigabytes would use allocation linked above contiguous to make more efficient use of disk space and reduce the time needed to maintain unity. I would also like the design of a direct access method for a sequential access one to make the most use of hardware strengths. The directory structure would be based tree to allow better organization of the information on the disk and allow for acyclic directory to make it easier for multiple users to work on the same project. It would also have a file security system that allowed for the different access rights for different user groups and password protection on indices and individual file system files.Several that already implement the features I described above as suitable for a hard drive 10 gigs are currently available, these include NTFS for Windows NT and XP operating systems and ext2 which is used in Linux.
Sincerely,
MBC Sam Harnett Master
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