Files

• A file is a named collection of related information, usually as a sequence of bytes, with two views:
  • Logical (programmer's) view, as the users see it.
  • Physical (operating system) view, as it actually resides on secondary storage.
• What is the difference between a file and a data structure in memory? Basically,
  • files are intended to be non-volatile; hence in principle, they are long lasting,
  • files are intended to be moved around (i.e., copied from one place to another), accessed by different programs and users, and so on.
• File lifetime is independent of process lifetime
• Used to share data between processes
• Input to applications is by means of a file
• File Management; File management system is considered part of the operating system
  • Manages a trusted, shared resource
  • Bridges the gap between:
    • lowlevel disk organization (an array of blocks),
    • and the user's views (a stream or collection of records)
  • Also includes tools outside the kernel; E.g. formatting, recovery, defrag, consistency, and backup utilities.
  • Objectives for a File Management System;
    • Provide a convenient naming system for files
    • Provide uniform I/O support for a variety of storage device types
    • Provide a standardized set of I/O interface routines
    • Guarantee that the data in the file are valid
    • Optimize performance
    • Minimize or eliminate the potential for lost or destroyed data
    • Provide I/O support and access control for multiple users
    • Support system administration (e.g., backups)