File System Structure and File Concepts

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is a file system comprised of?

A collection of data on primary storage devices

A collection of files and directory structure on secondary storage (correct)

A group of programs for file management

A single large storage device

What is a file?

A collection of software on a computer

A type of operating system

A collection of data normally stored on a secondary storage device (correct)

A folder on a computer

What are file types?

Classifying files by their creation date

Classifying files by their storage location

Classifying the content of a file, such as data, numeric, character, or binary (correct)

Classifying files by their size

What is one of the file attributes?

File location on device Signup and view all the answers

What is the purpose of the directory structure?

To provide information about all files in the system Signup and view all the answers

What is one of the basic file operations?

Create Signup and view all the answers

What happens during the 'seek' file operation?

The file is repositioned within the file system Signup and view all the answers

What happens during the 'open' file operation?

The directory structure is searched for the file entry Signup and view all the answers

What is the primary purpose of a cycle detection algorithm in a file system?

To determine whether a new link completes a cycle Signup and view all the answers

What is the main reason why protection is necessary in a file system?

To prevent users from accidentally destroying someone else's information Signup and view all the answers

What type of access control is associated with each file and directory?

Access-control list (ACL) Signup and view all the answers

What is a limitation of using access-control lists (ACLs)?

List construction can be a time-consuming task Signup and view all the answers

What is an alternative approach to access control lists (ACLs) in file systems?

Associating a password with each file or directory Signup and view all the answers

In a UNIX-based file system, what are the three classes of users that can have access to a file or directory?

Owner, group, and universe Signup and view all the answers

What is the purpose of the open-file table?

To contain information about all open files Signup and view all the answers

What type of file structure is required by the OS for an executable file?

Specific structure understood by the OS Signup and view all the answers

What is the most common access method used by editors and compilers?

Sequential Access Signup and view all the answers

What is the purpose of an index file?

To store an index into another file Signup and view all the answers

What is the directory structure?

A collection of nodes containing information about all files Signup and view all the answers

What is the purpose of the file pointer?

To track the last read/write location as a current file position Signup and view all the answers

What happens when the open count of a file reaches 0?

The file's entry is removed from the open file table Signup and view all the answers

What is the purpose of the disk location of a file?

To track the file's location on disk Signup and view all the answers

What is the main difference between sequential access and direct access?

Sequential access processes files in order, while direct access allows programs to read/write records rapidly in no particular order Signup and view all the answers

What is the purpose of the directory?

To contain information about all files on the partition Signup and view all the answers

What is the primary benefit of a tree-structured directory system?

Grouping capability Signup and view all the answers

What is the limitation of a single-level directory system?

All of the above Signup and view all the answers

What is the purpose of a Master File Directory (MFD) in a two-level directory system?

To be searched when a user logs in Signup and view all the answers

What is the result of deleting a directory in some systems like UNIX?

The entire directory structure is removed Signup and view all the answers

What is the problem with deleting a file in an acyclic-graph directory system?

Dangling pointers are created Signup and view all the answers

What is the solution to the deletion problem in an acyclic-graph directory system?

Preserve the file until all references to it are deleted Signup and view all the answers

What is the purpose of a link in an acyclic-graph directory system?

To point to another file or subdirectory Signup and view all the answers

What is the benefit of using a tree-structured directory system?

Efficient searching and grouping capability Signup and view all the answers

What is the result of starting with a two-level directory and allowing users to create subdirectories?

A general graph directory system Signup and view all the answers

What is the criteria for deleting a file in a general graph directory system?

When the reference count is 0 Signup and view all the answers

Study Notes

File System (FS) Structure

A file system consists of a collection of files, a directory structure, and resides on secondary storage devices (disks).
The directory structure provides information about all files in the system.

File Concept

A file is a collection of data stored on a secondary storage device.
File types classify the content of the file, such as:
- Data (numeric, character, binary)
- Program (contents defined by the file's creator)
- Many types (e.g., text file, source file, executable file)

File Attributes

A file has several attributes, which vary from one operating system (OS) to another, but typically include:
- Name (only information kept in human-readable form)
- Type (needed for systems that support different types)
- Location (pointer to file location on device)
- Size (current file size)
- Protection (controls who can read, write, execute)
- Time, date, and user identification (useful for protection, security, and usage monitoring)

File Operations

An OS must provide a number of operations associated with files, including:
- Create (find space in the file system and make an entry for the new file in the directory)
- Write (make a system call specifying the file name and information to be written)
- Read (use a system call specifying the file's name and where to put the next block)
- Seek (repositioning within a file, searching the directory for the appropriate entry)
- Delete (search the directory for the named file and erase the directory entry)
- Truncate (erase the contents of a file but keep its attributes)
- Open (search the directory structure on disk for the entry and move the content to memory)
- Close (move the content of the entry in memory to the directory structure on disk)

Open Files

Most file operations involve searching the directory for the entry associated with the named file.
To avoid searching, the OS keeps a table containing information about open files, including:
- Open-file table
- File pointer (tracks the last read/write location)
- File-open count (counts the number of times a file is open by multiple processes)
- Disk location of the file (info needed to locate the file on a disk)

File Structure

Files must conform to a required structure understood by the OS.
File structures can be:
- None (sequence of words, bytes)
- Simple record structure
- Lines
- Fixed length
- Variable length
- Complex structures (e.g., formatted document, relocatable load file)

Access Methods

Information stored in files must be accessed and read into memory.
Access methods include:
- Sequential Access (information is processed in order, one record after another)
- Direct Access / Relative Access (file is made up of fixed-length logical records, allowing rapid access to specific records)

Directory Structure

A collection of nodes containing information about all files.
Directory files contain information about files, including:
- Name
- Location
- Size
- Type
Both the directory structure and the files reside on disk.

Directory Organization

Efficiency (locating a file quickly)
Naming (convenient to users)
Two users can have the same name for different files.
The same file can have several different names.
Grouping (logical grouping of files by properties)

Operations Performed on Directory

Search for a file
Create a file
Delete a file
List a directory
Rename a file
Traverse the file system

Protection

Protection is needed to prevent accidental or deliberate destruction of someone else's information.
Information is private and should not be read by other users.
The OS must provide means to protect the information in the file system.
Many types of operations can be controlled, including:
- Read
- Write
- Execute
- Append
- Delete
- List

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Learn about the basics of file systems, including the structure and file types such as data, numeric, character, and binary. Understand how files are stored on secondary storage devices.