File Systems
COMP755 Advanced Operating
Systems 1
File Systems
COMP755 Advanced Operating
Systems
OS Purpose
• An operating system maps a logical
concept onto the physical hardware.
• The OS makes disk drives (of various
makes and models) with cylinders, heads
and sectors look like files with names,
security and data streams.
Goals of a File System
• Easily identify files
• Provide secure access
• Allow sharing of data
• Allocate disk space
• Provide rapid access
• Protection against loss of data
• Be hardware transparent
Types of Files
• To the OS, bits are bits, the file type
doesn’t matter.
• The OS provides low level functionality
upon which higher level file structures can
be built.
• Basic OS I/O functions are:
– read a block, write a block, open, close and
delete
Logical File Structure
• Most modern systems use a directory tree
structure
• A file can be uniquely specified by it’s
position in the tree,
/here/there/file.type
• Both files and directories have access
rights.
• To the OS, directories are just files
containing the names of other files.
• Disk space is allocated in units, often
called clusters.
• I/O must be done on a sector or cluster
basis.
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