Fall 2000M.B. Ibáñez Lecture 22 File-System I File Concept

Fall 2000M.B. Ibáñez File System From a user’s point of view, the file system is perhaps the most important part of the OS –He/she wants rapid access –SO must guarantees that the files will not be corrupted –The files must be secure from authorized access

Fall 2000M.B. Ibáñez File Management System The way a user of application may access files Programmer does not need to develop file management software From Operating Systems. Internals and Design Principles. W. Stalling. Prentice Hall

Fall 2000M.B. Ibáñez File System Software Architecture Pile Sequential Indexed Sequential Indexed Hashed Logical I/O Basic I/O Supervisor Basic File System Disk Device Driver Tape Device Driver User Program From Operating Systems. Internals and Design Principles. W. Stalling. Prentice Hall

Fall 2000M.B. Ibáñez Basic File System Physical I/O Deals with exchanging blocks of data Concerned with the placement of blocks Concerned with buffering blocks in main memory From Operating Systems. Internals and Design Principles. W. Stalling. Prentice Hall

Fall 2000M.B. Ibáñez Logical I/O Allows users and applications to access records Maintains basic data about file From Operating Systems. Internals and Design Principles. W. Stalling. Prentice Hall

Fall 2000M.B. Ibáñez Access Method Reflect different file structures Different ways to store and process data From Operating Systems. Internals and Design Principles. W. Stalling. Prentice Hall

Fall 2000M.B. Ibáñez Functions of File Management Identify and locate a selected file Use a directory to describe the location of all files plus their attributes On a shared system describe user access control Blocking for access to files Allocate files to free blocks Manage free storage for available From Operating Systems. Internals and Design Principles. W. Stalling. Prentice Hall

Fall 2000M.B. Ibáñez File System It is the part of the Operating System which consists of –An interface to the user –Data structures and algorithms needed by the Operating System to implement that interface

Fall 2000M.B. Ibáñez Files Used for input to a program Output of application saved in a file for long-term storage From Operating Systems. Internals and Design Principles. W. Stalling. Prentice Hall

Fall 2000M.B. Ibáñez Terms Used with Files Field –basic element of data –contains a single value –characterized by its length and data type Record –collection of related fields –treated as a unit Example: employee record From Operating Systems. Internals and Design Principles. W. Stalling. Prentice Hall

Fall 2000M.B. Ibáñez Terms Used with Files File –collection of similar records –treated as a single entity –have unique file names –may restrict access Database –collection of related data –relationships exist among elements From Operating Systems. Internals and Design Principles. W. Stalling. Prentice Hall

Fall 2000M.B. Ibáñez File Attributes Name – only information kept in human-readable form. Type – needed for systems that support different types. Location – pointer to file location on device. Size – current file size. Protection – controls who can do reading, writing, executing. Time, date, and user identification – data for protection, security, and usage monitoring. Information about files are kept in the directory structure, which is maintained on the disk. From Operating System Concepts. Silberschatz & Galvin. Addison Wesley

Fall 2000M.B. Ibáñez File Operations create write read reposition within file – file seek delete truncate open(F i ) – search the directory structure on disk for entry F i, and move the content of entry to memory. close (F i ) – move the content of entry F i in memory to directory structure on disk. From Operating System Concepts. Silberschatz & Galvin. Addison Wesley

Fall 2000M.B. Ibáñez File Types – name, extension