Standard File Hierarchies

Topic 2.3 focuses on the two most common standard file hierarchies: Microsoft Windows and POSIX (Linux).
These standards dictate the location of important files for the respective operating systems.
The standardization ensures that the OS and applications can locate essential libraries and data.
Standardized locations group similar data in known directories, simplifying the system.
Application developers know where to place and find ancillary components.
System administrators know where to look for log files and other critical data.
Even regular end-users benefit from knowing the standard locations of applications and configurations.

Users can explore the file system by opening the file browser and navigating to the C drive.
Key directories:
- Program Files and Program Files (x86): Store executable system files and end-user applications.
  - 32-bit applications are stored in Program Files (x86) due to Windows' ability to emulate older architectures.
- Users: Contains home directories/folders for user accounts on the Windows machine.
- Windows: Contains all operating system resources.
  - Should be treated as read-only.
  - Subdirectories:
    - System32: Contains utilities and libraries.
    - System32\Drivers: Contains drivers for hardware devices.
- Temp: Contains temporary files created by applications.
  - Files may persist after a reboot and can be cleaned by the OS or user.
Key differences from POSIX file systems:
- Devices/hard disks are referenced by a letter followed by a colon (e.g., C:).
- Paths are separated by backslashes (e.g., Windows\System32).
- Other operating systems and web browsers use forward slashes in paths (URLs).

POSIX systems are older than Windows and have evolved organically since the 1970s.
Backward compatibility is crucial, so the structure remains largely unchanged.
The root of the file system is denoted by a forward slash (/).
Any other mounted file systems reside within this hierarchy.
Key directories:
- /home: User home directories (equivalent to the 'Users' directory in Windows).
- /tmp: Temporary files.
- /bin: Important system programs (binary files).
- /sbin: Important system administration tools.
- /var: Log files. Subdirectories exist for different services (e.g., web server logs).
- /etc: System and program configuration files.
  - Configuration files are typically text files, unlike Windows, which uses a registry.
- /usr: Executable programs, structured text, library files, and documentation used by end-users but not part of the core OS.
  - /usr/bin: Programs created/stored by users.
  - /usr/lib: Library files for user-oriented programs.
  - /usr/share: Documentation, including man pages.

Demonstration of navigating the POSIX file system using a terminal.
Commands:
- pwd: Present working directory. Displays the current directory.
- cd: Change directory. Used to navigate the file system (cd / goes to the root directory).
- ls: Lists files and directories in the current directory.
- ls -l: Long listing, provides more information about files and directories (permissions, size, modification date, etc.).
- tree: Displays the file system in a tree-like diagram.
  - tree -d -L 1: Restricts the output to directories only and limits the depth to one level below the current directory.
File types indicated in the long listing:
- d: Directory.
- l: Symbolic link.
- -: Regular file.

/etc: Contains system and application configuration.
- fstab: Table of file systems mounted at boot.
- Password files.
- Network information.
- Time zone configuration.
/bin: Essential command binaries.
- ls: Lists directory contents.

Slide 33 lists additional references for learning more about standard file locations for Linux and macOS.