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 they function may vary. For example, to perform the delete file operation in a modern file system like NTFS that has file protection built into it would be more complicated than the same operation in an older file system like FAT. Both systems would first check to see whether the file was in use before continuing, NTFS would then have to check whether the user currently deleting the file has permission to do so.
Some file systems also allow multiple people to open the same file simultaneously and have to decide whether users have permission to write a file back to the disk if other users currently have it open. If two users have read and write permission to file should one be allowed to overwrite it while the other still has it open? Or if one user has read-write permission and another only has read permission on a file should the user with write permission be allowed to overwrite it if theres no chance of the other user also trying to do so?
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Different file systems also support different access methods. The simplest method of accessing information in a file is sequential access. This is where the information in a file is accessed from the beginning one record at a time. To change the position in a file it can be rewound or forwarded a number of records or reset to the beginning of the file. This access method is based on file storage systems for tape drive but works as well on sequential access devices (like mordern DAT tape drives) as it does on random-access ones (like hard drives). Although this method is very simple in its operation and ideally suited for certain tasks such as playing media it is very inneficient for more complex tasks such as database management.
A more modern approach that better facilitates reading tasks that arent likely to be sequential is direct access. direct access allows records to be read or written over in any order the application requires. This method of allowing any part of the file to be read in any order is better suited to modern hard drives as they too allow any part of the drive to be read in any order with little reduction in transfer rate. Direct access is better suited to to most applications than sequential access as it is designed around the most common storage medium in use today as opposed to one that isnt used very much anymore except for large offline back-ups. Given the way direct access works it is also possible to build other access methods on top of direct access such as sequential access or creating an index of all the records of the file speeding to speed up finding data in a file.
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On top of storing and managing files on a drive the file system also maintains a system of directories in which the files are referenced. Modern hard drives store hundreds of gigabytes. The file system helps organise this data by dividing it up into directories. A directory can contain files or more directories. Like files there are several basic operation that a file system needs to a be able to perform on its directory structure to function properly.
It needs to be able to create a file. This is also covered by the overview of peration on a file but as well as creating the file it needs to be added to the directory structure.
When a file is deleted the space taken up by the file needs to be marked as free space. The file itself also needs to be removed from the directory structure.
Files may need to be renamed. This requires an alteration to the directory structure but the file itself remains un-changed.
1 comment
Good explanation, however, you've only appealed to less than 5 of your target reading audience with a text only article. When explaining concepts that readers cannot see, you need to be sure to show visual representations or illustrations to help get your point across. Most readers are visual learners. Thank you for the article. It was well written.
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