File Systems and Directory Operations Quiz

Operating Systems

• The lecture covered a range of topics related to operating systems, specifically focusing on file system management.
• A file system consists of files, each storing related data, a directory structure organizing files, and partitions for large collections of directories.
• The fundamental function of a file system is managing and accessing data and programs.
• Physical storage units are the actual storage media (disks, tapes, optical drives), while logical storage units are files mapped onto physical devices by the operating system.
• A computer file is a named collection of related information stored on secondary storage, acting as the smallest logical storage unit.

File System Parts

• File systems are composed of files, each storing related data.
• Directory structures organize and provide information about all files within a system.
• Partitions separate physically or logically large collections of directories.

File System Function

• The file system manages and accesses data and programs.

Physical vs. Logical Storage Unit

• Physical storage units are the physical devices used for storage.
• Logical storage units are files.
• The operating system maps files onto physical storage devices.

Definition of Computer File

• A file is a named collection of related information stored on a secondary storage device.
• Files are sequences of bits, bytes, lines, or records defined by their creator and user.
• Data cannot be written to secondary storage unless it's part of a file.
• Typically, files represent programs (source and object code) and data.

File Types

• File types include source programs, object programs, executable programs, and data files (containing numeric data, text, images, and sound).

File Structure

• Files have defined structures based on their type.
• Text files are sequences of characters.
• Source files include subroutines and functions.
• Object files are in a format understandable by the linker.
• Executable files are code sections executable by the loader.

File Attributes

• Files have attributes like a name (per user), an identifier (unique to the system), a data type, location on a physical device, size, protection info, and time/date information (creation, modification, last use).
• File information is maintained in directory structures on secondary storage.
• File attributes are included in their respective directory entries.

Files Operations

• Operating systems provide system calls for creating, writing, reading, repositioning, deleting, and truncating files.
• These operations involve 12 different file actions.

Open-File-Table

• File operations often involve searching the directory.
• The open-file-table (a small table in the operating system) caches information about open files, speeding up subsequent operations.
• When a file operation occurs, the file is specified by its index in the open-file-table, avoiding directory searches.
• OS includes file types within the filename (e.g., "image.png"). The name and extension are separated by a period.

How OS implements File Types

• File types are often implemented by including the type as part of the filename.
• The naming convention uses a period to separate the name from the extension.

Why OS implements File Types

• The OS uses extensions to determine file types and the operations that can be performed on them.
• Extensions indicate the appropriate application programs for opening and working with files.

Common File Types

• Common file types include their extensions and functionalities—for example, .exe files are executable, and .txt files are text files.

Why Files must have Extension

• Extensions help determine a file type.
• Determine how files can be processed.
• Indicate which application program should open the files.

How OS organizes Files

• Operating systems organize files in large storage units—partitions or volumes—which behave as separate storage.
• Directories are a key part of how files are organized.

Directory Operations

• Directory operations include searching for a file, creating a file, deleting a file, and listing a directory /renaming a file.

Directory

• A directory is a collection of files containing information about the files (e.g. attributes, location, and ownership).
• Operating systems manage most of the directory functionality.

Directory Content

• Device directories contain information like file name, type, address, current and maximum length, date last accessed and updated information, owner info, and protection.

Advantages of Directories

• Directories improve efficiency by allowing quick file location.
• They aid in naming, permitting multiple users to have different files with the same name (e.g., 'mailbox' for each user).
• Directories facilitate grouping similarly-used files.

Directory Structure

• Operating systems use diverse directory systems (single-level, two-level, tree-structure, and acyclic-graph).

Single-Level Directory System

• One directory that collects all files.
• Simpler for single-user systems, useful in early personal computer systems.
• Can lead to conflicts when multiple users share a system.

Two-Level Directory System

• Combines a master directory (MFD) with user directories(UFDs).
• Helps avoid naming issues
• Requires users to specify both user directories and the file name whenever accessing another user's files.

Tree-Structure Directory System

• Files organized in a hierarchical tree structure, useful for files.
• Allow users to create subdirectories.
• Using unique directory names (paths) avoid name conflicts.

Acyclic-Graph Directory Systems

• Enable file and directory sharing amongst different users.
• Allows directories and files to be shared.
• Offers flexibility(e.g shared directories).

File Access Methods

• Three common methods for accessing files: sequential, direct (random), and indexed.
• These methods affect how files are read and written on a disk.

Sequential Access Method

• Files processed sequentially, block by block.
• Cannot access a specific record until previous blocks are read.

Direct Access Method

• Records accessed directly via "record numbers."
• Suitable for applications where random access to parts of a file are common.

Indexed Access Method

• Files contain indexes, giving access to the indexed record quickly.
• Not well suited for large files: indexes can become too large to keep in memory

Disk Allocation Methods

• Methods used to allocate space on the disk, includes contiguous, linked, indexed, file allocation table (FAT) methods, disk space.

Contiguous Allocation Method

• Files stored in contiguous disk blocks.
• Requires knowing the filesize during creation.

Linked Allocation Method

• Files stored in non-contiguous blocks, linked by pointers.
• Allows files to grow without need to know the file size.
• Not suitable for direct access.

Indexed Allocation Method

• Files have an index block, storing the addresses of the file's blocks
• Easy to access files directly, good for searching.
• Index block can be large, potentially limiting applicability to medium-sized files.

File Allocation Table (FAT)

• FAT is a table that tracks file locations on a disk
• Directory entries point to the starting block of a file, and the FAT records the rest of the blocks(sequential).
• FAT must be loaded into memory to operate(can be a drawback when dealing with large amounts of data).

Data Reliability/Protection

• Data reliability measures include backing up files, disks and data, and making periodic copies to ensure data loss is minimized.
• Data protection mechanisms control access to files/folders to avoid unauthorized operations or damage.

Access Control List (ACL)

• ACL is a list of users/groups and their access permissions (e.g write, read, execute, delete) for a file/directory.

Passwords

• Passwords can be used to control file access.

Test your knowledge on file systems, directory operations, and file types with this comprehensive quiz. Covering questions on executable files, multimedia file extensions, and organizational methods, this quiz will enhance your understanding of how file systems work. Perfect for students in computer science or information technology courses.