File Organisation and Access

Introduction

This section explores how files are organised and accessed within a computer system. Understanding these concepts is fundamental to managing data efficiently.

File Systems

A file system is the method and data structure used by an operating system to control how data is stored and retrieved. It defines how files are named, stored, and accessed on a storage device.

Common file systems include FAT32, NTFS, and ext4.

File Organisation Methods

There are several ways files can be organised within a file system:

• Sequential: Files are stored one after the other on the storage device.
• Indexed: A file index is created, containing pointers to the different parts of the file. This allows for faster access to specific data.
• Hierarchical (Tree-structured): Files are organised into a tree-like structure of directories (folders) and subdirectories. This is the most common method used in modern operating systems.

Hierarchical File Systems in Detail

The hierarchical structure uses directories to group related files. This provides a logical organisation and makes it easier to find files.

Each directory can contain files and further subdirectories, creating a tree-like structure.

File Access Methods

Operating systems provide various methods for accessing files. These methods differ in their speed and suitability for different tasks.

Sequential Access

Description	How it works	Advantages	Disadvantages
Sequential Access	Files are accessed in the order they are stored on the storage device.	Simple to implement.	Slow for accessing specific data within a file.

Random Access

Description	How it works	Advantages	Disadvantages
Random Access	Any part of a file can be accessed directly, regardless of its position on the storage device.	Fast for accessing specific data.	More complex to implement.

Direct Access

Direct access is a type of random access where the location of data within a file is known. This is typically used with magnetic disks.

Indirect Access

Indirect access involves using pointers or indexes to locate data within a file. This is often used with larger files to reduce storage space.

File Access Techniques

Different techniques are used to access files, depending on the operating system and the type of access required.

• File Handle: A file handle is a reference to an open file. It allows the operating system to track the file and manage access permissions.
• Pointers: Pointers store the physical location of data within a file. They are used in indirect access methods.
• Buffers: Buffers are temporary storage areas used to hold data being read from or written to a file. This can improve performance.

File Permissions

File permissions control who can access a file and what operations they can perform (e.g., read, write, execute). These are crucial for data security.

Permissions are typically assigned to the owner, the group, and others.

Summary

Understanding file organisation and access methods is essential for efficient data management. The choice of file system and access method depends on the specific requirements of the application.