L30_Ch12a

Chapter 12: File Management (Part A: Sections 12.1-12.2)

Page 1: Introduction

• Overview of key topics in file management including structures and systems.

Page 2: Chapter Overview

• Key concepts covered in the chapter:

  • File structure

  • File management systems

  • File organization and access

  • Various file types including:

    • The pile

    • The sequential file

    • The indexed sequential file

    • The indexed file

    • The direct or hashed file

  • B-Trees (important)

  • File directories and organization

  • Naming conventions

  • Sharing and access rights

  • Secondary storage management strategies

  • File allocation and free space management

  • Reliability considerations

  • Operating system-specific file management: Android, SQLite, UNIX, and Windows NTFS.

Page 3: Understanding Files

• Files:

  • Data collections created by users.

  • Crucial part of the OS impacting user interaction.

• Desirable properties of files include:

  • Long-term existence (stored on secondary storage).

  • Shareable between processes with access permissions.

  • Structured in a hierarchical or complex manner to reflect relationships.

Page 4: File Systems

• Role of file systems:

  • Store data organized as files.

  • Provide functions for managing files, such as:

    • Create, delete, open, close, read, write.

  • Maintain file metadata (attributes).

Page 5: File Structure Terminology

• Four key terms in file discussions:

  • Field: Basic data portion containing a single value.

  • Record: Collection of related fields.

  • File: Collection of related records.

  • Database: Wider collection of records managing relationships among data.

Page 6: File Structure Details

• Field:

  • Basic unit of data; can be fixed or variable length.

• Record:

  • Related fields treated as a unit. Can vary in length.

• Database:

  • Collection of similar records, referenced by name, with access controls.

Page 7: Importance of File Management Systems

• Essential aspects of an OS:

  • Meet data management needs of users.

  • Validate data integrity.

  • Optimize performance for data transfers.

  • Support various storage devices.

  • Minimize data loss risks.

  • Standardized I/O routines for file access.

Page 8: User Requirements in File Management

• Users need to:

  • Create, delete, read, and write files.

  • Control access to their files.

  • Move data between files.

  • Back up and recover files.

  • Access files by name, not just numeric identifiers.

Page 9: File Access Methods

• Types of file access methods include:

  • Indexed sequential, pile, sequential.

• Diagram (Figure 12.1) illustrates file system software architecture.

Page 10: Device Drivers

• Lowest level of file management:

  • Direct communication with peripheral devices.

  • Responsible for initiating and completing I/O operations.

Page 11: Basic File System

• Also called the physical I/O level.

• Manages data blocks exchanged with storage devices.

• Concerned with data placement and buffering, rather than content understanding.

Page 12: Basic I/O Supervisor

• Handles initiation and termination of file I/O.

• Maintains control structures for device scheduling and file statuses.

Page 13: Logical I/O

• Facilitates user and application record access.

• Provides general-purpose record I/O capabilities.

Page 14: File Access Method

• Closest level of the file system to user.

• Standard interface for applications accessing data.

• Different methods correspond to file structures and access styles.

Page 15: Important Terminology - "Blocking"

• Blocking in Processes: When a process waits.

• Blocking in File Systems: Packing data into portions (blocks).

Page 16: Directory Management and More

• Key aspects of file management include:

  • Access methods, blocking, disk scheduling, file allocation, and structure management.

Page 17: File Organization and Access

• Logical structuring of records based on access methods.

• Criteria for file organization:

  • Short access time, ease of update, storage economy, maintenance simplicity, reliability.

Page 18: File Organization Types

• Common file organizations include:

  • Pile

  • Sequential

  • Indexed sequential

  • Indexed

  • Direct/hashed files.

Page 19: Common File Organizations

• Characteristics of different file types:

  • Pile File: Variable-length records, unordered.

  • Sequential File: Fixed format, key-field based.

  • Indexed Sequential: Uses indexes for efficient access.

Page 20: Pile File

• Simplest file organization form:

  • Collects data in arrival order.

  • Records accessed via exhaustive search.

Page 21: Sequential File

• Most common file structure:

  • Fixed record format; key field identifies records.

  • Suited for batch applications; easily stored on tape and disk.

Page 22: Indexed Sequential File

• Random access supported via an index.

• Reduces time to access records; allows multiple indexing levels.

Page 23: Indexed File

• Access through indices only.

• Used in time-critical applications (e.g., airline reservations).

Page 24: Direct/Hashed File

• Allows direct access to known addresses via hashing.

• Suitable for quick access environments.

Page 25: Homework Assignment

• Investigate internal structures of different file types:

  • *.JPG, *.MP3, *.DOC, *.XLS.

• Classify them into discussed file types.