File Systems and Storage Overview

File Systems and Storage

• File systems manage how computer files are stored and accessed.
• Files are organized in a logical address space (contiguous).
• Data types include numeric, character, and binary.
• Programs also occupy this logical address space.

File Attributes

• Name - human-readable file identification.
• Identifier - unique tag identifying a file within the system.
• Type - helps differentiate types of files.
• Location - pointer indicating file position on the device.
• Size - current file size.
• Protection - controls user access levels (read, write, execute).
• Time, date, and user identification - data for security and usage tracking.
• Information about files is stored in a directory structure maintained on the disk.

File Operations

• File is an abstract data type.
• Operations include: create, write, read, reposition within file, delete.

File Types - Name, Extension

• File types are associated with different functionalities and formats.
• Examples: Executable (.exe, .com, .bin), Object (.obj, .o), Batch (.bat, .sh), Text (.txt, .doc), Word Processor (.doc, .rtf, .tex), Library (.lib, .a, .so, .dll), Print or View (.ps, .pdf, .jpg), Archive (.arc, .zip, .tar), Multimedia (.mpeg, .mov, .rm, .mp3, .avi).

Access Methods

• Sequential Access: Reading/writing occurs sequentially, starting from the beginning.
• Direct Access: Reading/writing occurs directly to a specific block location via its relative block number.

Sequential-access File

• Conceptual representation of a file as a linear sequence of data blocks.

Example of Index and Relative Files

• An index file provides a lookup table to find the location (relative block number) in the relative file.

Directory Structure

• A directory is a collection of nodes.
• These nodes contain information about the files.
• Files and the directory structure reside on the disk.

Disk Structure

• Disks can be partitioned for fault tolerance.
• A disk partition can be used in a raw mode or formatted with a file system.
• Partitions are also known as minidisks or slices.
• An entity holding a file system is known as a volume.
• Volumes manage file system metadata (device directory/volume table).
• Special-purpose file systems often exist alongside general-purpose ones within the same OS or computer.

A Typical File-system Organization

• Partitions with directories and files.

Operations Performed on Directory

• Directory operations include search, create, delete, list, rename, and traversal.

Single-Level Directory

• A single directory for all users.
• Challenges include naming conflicts and lack of organization.

Two-Level Directory

• Dedicated directory for each user.
• Problem: same file name for different users
• Advantages: efficient searching, organization of files per user.

Tree-Structured Directories

• Hierarchical directory structure.
• Efficient searching, grouping files.
• Current directory/working directory
• Operations like cd, type.

Tree-Structured Directories (Cont)

• Path names (absolute/relative) within a tree structure.
• Directory operations(create,delete,rename)

Access Lists and Groups

• Different access modes (read, write, execute).
• User, group, public permissions
• Groups and chmod
• Windows XP ACL Management (example of Access Control List)

A Sample UNIX Directory Listing

• Example showing different folder permissions and listings (-rw-rw-r--, etc.).

File-System Implementation

• Boot control block (OS booting info).
• Volume control block details info about volume.
• Directory structure organizes files.
• Per-file File Control Block (FCB) for storage of file details.

A Typical File Control Block

• Summarization of components within the FCB (file permissions, dates, owner, group, ACL, size, data blocks).

Allocation Methods

• How disk blocks are assigned to files: contiguous, linked, and indexed allocation.

Contiguous Allocation

• File blocks are stored sequentially on the disk.
• Simple, efficient random access but inefficient regarding space.

Contiguous Allocation of Disk Space

• Example illustration of contiguous allocation with assigned blocks and counts.

Linked Allocation

• Blocks can be anywhere on the disk as they are linked in a chain of pointers.
• Handles file growth because file grows in contiguous blocks.

Linked Allocation

• Conceptual illustration of linked lists of disk blocks.

File-Allocation Table

• Table associating file names with start blocks, often used with linked allocation.

Indexed Allocation

• All pointers to blocks are collected in an index block.
• Efficient random access but index requires extra storage.

Example of Indexed Allocation

• Demonstrates how file blocks are tied to the index block using pointers.

This quiz covers essential concepts related to file systems and storage, including file attributes, operations, and types. It provides an understanding of how files are organized and managed within a computer system, along with their associated functionalities. Perfect for students and professionals looking to enhance their knowledge in computer science.