(file systems)12312321321321312312312.pptx
- 1. MIT 201- ADVANCED OPERATING SYSTERM AND NETWORKING Instructor: JOHN ED AUGUSTUS ESCORIAL , MIT Presenter: VAN O. AMPANG
- 2. File Systems, File System Performance
- 3. CHAPTER OBJECTIVES • To discuss what is file systems. • To explain the function of file systems. • To discuss file concept, file attributes, and file operations. • To explain access methods (including sequential and direct method) , and directory overview.
- 4. What is file system?
- 5. For most users, the file system is the most visible aspect of an operating system. It provides the mechanism for on-line storage of and access to both data and programs of the operating system and all the users of the computer system.
- 6. File Concept Computers can store information on various storage media, such as magnetic disks, magnetic tapes, and optical disks.
- 7. File Attributes A file is named, for the convenience of its human users, and is referred to by its name.
- 8. A file’s attributes vary from one operating system to another but typically consist of these:
- 9. • Name. The symbolic file name is the only information kept in human readable form. • Identifier. This unique tag, usually a number, identifies the file within the file system; it is the non-human-readable name for the file. • Type. This information is needed for systems that support different types of files. • Location. This information is a pointer to a device and to the location of the file on that device.
- 10. • Size. The current size of the file (in bytes, words, or blocks) and possibly the maximum allowed size are included in this attribute. • Protection. Access-control information determines who can do reading, writing, executing, and so on. • Time, date, and user identification. This information may be kept for creation, last modification, and last use. These data can be useful for protection, security, and usage monitoring.
- 11. File Operations A file is an abstract data type. To define a file properly, we need to consider the operations that can be performed on files.
- 12. Six basic file operations:
- 13. • Creating a file. Two steps are necessary to create a file. • Writing a file. To write a file, we make a system call specifying both the name of the file and the information to be written to the file • Reading a file. To read from a file, we use a system call that specifies the name of the file and where (in memory) the next block of the file should be put.
- 14. • Repositioning within a file. The directory is searched for the appropriate entry, and the current-file-position pointer is repositioned to a given value. • Deleting a file. To delete a file, we search the directory for the named file. • Truncating a file. The user may want to erase the contents of a file but keep its attributes.
- 15. File Types When we design a file system—indeed, an entire operating system—we always consider whether the operating system should recognize and support file types.
- 17. File Structure File types also can be used to indicate the internal structure of the file.
- 18. Internal File Structure Internally, locating an offset within a file can be complicated for the operating system.
- 19. Access Methods Files store information. When it is used, this information must be accessed and read into computer memory.
- 20. Sequential Access The simplest access method is sequential access. Information in the file is processed in order, one record after the other.
- 21. Direct Access Another method is direct access (or relative access). Here, a file is made up of fixed-length logical records that allow programs to read and write records rapidly in no particular order.
- 22. Other Access Methods Other access methods can be built on top of a direct- access method.
- 23. Directory Overview The directory can be viewed as a symbol table that translates file names into their directory entries.
- 24. When considering a particular directory structure, we need to keep in mind the operations that are to be performed on a directory:
- 25. • Search for a file. We need to be able to search a directory structure to find the entry for a particular file. • Create a file. New files need to be created and added to the directory. • Delete a file. When a file is no longer needed, we want to be able to remove it from the directory.
- 26. • List a directory. We need to be able to list the files in a directory and the contents of the directory entry for each file in the list. • Rename a file. Because the name of a file represents its contents to its users. • Traverse the file system. We may wish to access every directory and every file within a directory structure.
- 27. REFERENCE: • Gagne, Galvin, and Silberschatz. Operating-System-Concepts, 9th Edition, 2012
- 28. Thank you!