- Since main memory is usually too small to accommodate all the data and programs permanently, the computer system must provide secondary storage to back up main memory.
- The file system provides the mechanism for on-line storage of and (multiple) access to both data and programs residing on the disks.
- A file is a collection of related information defined by its creator.
- File Management System: Bridges the gap between low-level disk organization (an array of blocks) and the user's views (a stream or collection of records) (mapped).
- Some devices transfer a character or a block of characters at a time.
- Some can be accessed only sequentially, others randomly.
- Some transfer data synchronously, others asynchronously.
- Some are dedicated, some shared.
- They can be read-only or read-write.
- Also includes tools outside the kernel; formatting, recovery, defrag, consistency, backup utilities (system administration).
- In many ways, they are also the slowest major component of the computer.
- Files are managed by the OS. How they are structured, named, accessed, used, protected, and implemented are major topics in OS design.
- The file system consists of two distinct parts:
- a collection of files; each storing related data,
- a directory structure; which organizes and provides information about all the files in the system.
- Objectives for a file management system;
- Provide a convenient naming system for files.
- Provide a standardized set of I/O interface routines and provide access control for multiple users.
- Guarantee that the data in the file are valid. Minimize or eliminate the potential for lost or destroyed data.
- Optimize performance.
- How do you keep one user from reading another's data?
- How do you know which blocks are free?
Subsections
Cem Ozdogan
2011-02-14
