Files & File Systems: Crash Course Computer Science #20

Introduction to File Formats and Organization

In this section, we will learn about file formats and how computers organize files using file systems.

Understanding File Formats

• File formats are important for organizing data within a file.

• ASCII is a commonly used character encoding standard for text files.

• ASCII maps decimal numbers to corresponding characters.

• WAV files store audio data and contain metadata at the beginning of the file.

• BMP files store images as pixels with RGB values.

Organizing Files with File Systems

• File systems help computers keep track of files and their locations on storage devices.

• Metadata, such as file size, creation date, and permissions, is stored in the file system's directory structure.

• Different operating systems use different file systems, such as FAT32 or NTFS for Windows and ext4 for Linux.

Storing Files on Storage Devices

This section explores how computers store files using hardware and software abstractions.

Storage Mediums

• Computers can store data on various mediums like tapes, disks, or integrated circuits.

• Regardless of the medium used, storage is conceptualized as a line of buckets that hold values.

Hardware and Software Abstractions

• Hardware and software abstractions allow us to interact with storage devices without worrying about their physical characteristics.

• The operating system provides an interface to access storage devices through read/write operations.

Conclusion

File formats play a crucial role in organizing data within computer files. Understanding how different types of files are structured helps us interpret their contents accurately. Additionally, file systems enable efficient organization and retrieval of files on storage devices. By abstracting away the complexities of storage mediums, computers can effectively manage large amounts of data.

Understanding File Storage and Directory Files

In this section, we learn about file storage and the concept of directory files. We explore how computers store files and the need for a special file to record the location of other files.

Storing Multiple Files

• Computers need a way to store multiple files at once.

• The simplest option is to store files back-to-back, but this raises the question of how the computer knows where each file begins and ends.

• Storage devices have no notion of files; they are just mechanisms for storing bits.

• To address this, a special file called a Directory File is used to record the locations of other files.

Directory File

• The Directory File is kept at the front of storage so that its location is always known (usually at location zero).

• Inside the Directory File are the names of all other files in storage.

• Each file has a name followed by a period and ends with a file extension (e.g., "BMP" or "WAV").

• The Directory File also stores metadata about these files, such as creation date, last modification date, owner information, and permissions.

• Most importantly, it contains information about where these files begin in storage and their length.

Updating the Directory File

• Any changes made to files (adding, removing, renaming) require updating the information in the Directory File.

• This ensures that the table of contents remains accurate and matches the actual content.

Basic File System

• The maintenance of the Directory File exemplifies a basic file system's functionality within an operating system.

• This example represents a Flat File System where all files are stored at one level without any hierarchical structure.

Blocks and Fragmentation

• Modern file systems use blocks to store data. This allows for extra space called slack space for changes and aligns all file data to a common size for simplified management.

• Files can be broken up into chunks and stored across multiple blocks to accommodate their size.

• This allocation of blocks per file allows for easy expansion and shrinking of files.

• When a file is deleted, the corresponding block becomes free, but the data remains until overwritten.

Defragmentation

• Fragmentation occurs when files are created, deleted, and modified, leading to scattered storage locations.

• Defragmentation is the process of rearranging data so that files have blocks located together in storage and in the right order.

• Defragmenting improves file access speed by reducing seek time.

Hierarchical File System

• As computers' storage capacity increased, it became impractical to store all files at one level.

• Hierarchical File Systems organize related files into folders and subfolders for better organization and management.

Conclusion

In this section, we conclude our discussion on file storage systems by highlighting the importance of defragmentation and introducing hierarchical file systems.

Summary

• Understanding how computers store files is crucial for efficient data management.

• Directory Files play a vital role in recording file locations and metadata.

• Basic File Systems manage stored files through the maintenance of Directory Files.

• Blocks are used to store data, allowing for easy expansion or shrinking of files.

• Fragmentation occurs when files are created, deleted, or modified. Defragmentation helps optimize file access speed by rearranging data.

• Hierarchical File Systems provide a more organized approach to storing large numbers of files by using folders and subfolders.

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New Section Understanding File Systems

In this section, we will explore the concept of file systems and how they organize files and folders in a hierarchical structure.

Introduction to File Systems

• All files and folders are organized within a root directory.

• The root directory contains various file paths that lead to other files and folders.

• The format of the Directory File located in the root directory is the same as other directories.

Hierarchies and File Movement

• File systems allow for hierarchies of unlimited depth, making it easy to organize files.

• Moving files within the file system does not require rearranging data blocks.

• Modifying Directory Files allows for easy movement of files between directories.

Abstraction and Accessibility

• File systems provide a higher level of abstraction, hiding the underlying storage medium (e.g., magnetic tape or disks).

• Data is neatly organized into easily accessible files.

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New Section Exploring Music Directory

In this section, we will focus on the music directory within the file system and its contents.

Contents of Music Directory

• The music directory contains a collection of great songs.

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New Section Key Principles of File Systems

This section highlights important principles related to file systems.

Staying Organized

• When moving a file between directories, the actual location of the file remains unchanged.

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