File System
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File System consists of
✦ A collection of files
✦ A directory structure
✦ (possibly) partitions
Important Issues
✦ File protection
✦ The semantics of file sharing
File Concept:
• The operating system provides a uniform logical abstraction for the physical storage of information.
• Storage devices are nonvolatile.
• A file is a named collection of related information that is recorded on secondary storage.
• Contiguous logical address space
• Types:
- ✦ Data
- ✔ Numeric
- ✔ Character
- ✔ Binary
- ✦ Program
- ✔ Source, object and executable file formats
File Attributes:
• Name - only information kept in human-readable form.
• Identifier - a unique tag (i.e., an internal number) that identifies the file within the file system.
• Type - needed for systems that support different types.
• Location - a 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.
File Sharing:
• Sharing of files on multi-user systems is desirable.
• Sharing may be done through a protection scheme.
• On distributed systems, files may be shared across a network.
• Network File System (NFS) is a common distributed file sharing method
Protection:
File owner/creator should be able to control:
✦ what can be done
✦ by whom
Types of access:
✦ Read
✦ Write
✦ Execute
✦ Append
✦ Delete
✦ List
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