Difference between revisions of "File System"

Latest revision as of 16:42, 24 June 2012

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