File System in Operating System
Introduction
Computers can store information on various storage media
The operating system abstracts from the physical properties of its storage devices to define a logical storage unit called a file.
Files are mapped by the operating system onto non volatile physical devices.
A file is a named collection of related information that is recorded on secondary storage.
For a user's perspective, a file is the smallest allotment of logical secondary storage (i.e., data supposedly cannot be written to secondary storage unless written in a file).
Files commonly represent programs (both source and object code) and data.
Data file contents may be numeric, alphabetic, alphanumeric, or binary.
Files may be free form (e.g., text files) or rigidly formatted.
In general, a file is a sequence of bits, bytes, lines, or records, whose meaning is defined by the file's creator and user.
Many important applications need to store more information then have in virtual address space of a process.
Disks are used to store files
Information is stored in blocks on a disks
Can read and write blocks
We use file system as an abstraction to deal with accessing the information kept in blockks on a disk
Files are created by a process.
Thousands of them on a disk
Managed by the Operating System (OS)
OS structures them, names them, protects them
Two ways of looking at a file system
How do we name a file, protect it, organize the filesComputers can store information on various storage media
The operating system abstracts from the physical properties of its storage devices to define a logical storage unit called a file.
Files are mapped by the operating system onto non volatile physical devices.
A file is a named collection of related information that is recorded on secondary storage.
For a user's perspective, a file is the smallest allotment of logical secondary storage (i.e., data supposedly cannot be written to secondary storage unless written in a file).
Files commonly represent programs (both source and object code) and data.
Data file contents may be numeric, alphabetic, alphanumeric, or binary.
Files may be free form (e.g., text files) or rigidly formatted.
In general, a file is a sequence of bits, bytes, lines, or records, whose meaning is defined by the file's creator and user.
Many important applications need to store more information then have in virtual address space of a process.
- Must store large amounts of data
- Gigabytes -> terabytes -> petabytes
- Lifetime can be seconds to years
- Must have some way of finding it !
Disks are used to store files
Information is stored in blocks on a disks
Can read and write blocks
We use file system as an abstraction to deal with accessing the information kept in blockks on a disk
Files are created by a process.
Thousands of them on a disk
Managed by the Operating System (OS)
OS structures them, names them, protects them
Two ways of looking at a file system
- User point of view:
- Implementation point of view
Start with user, then go to implementation.
The user point of view
- Naming
- Structure
- File Type (directories)
- File Access
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