File Management and Access Methods in Operating Systems

Introduction to Operating Systems

• A computer system consists of user software, system software, hardware, and user applications.

Definition of Operating System

• An OS is a system software that manages all the system's hardware resources.
• It provides users with an environment to use system resources and run their own applications.
• The two primary objectives of an OS are to make a computer system convenient to use and manage the resources of a computer system.

Logical Architecture of a Computer System

• The operating system hides the details of the hardware from the programmer and provides a convenient interface for using the system.

Specific Terms and Concepts

• Batch systems: no user interaction
• Multiprogramming: multiple programs loaded in memory
• Time-sharing: each process receives slices of CPU time
• Interactive systems: provides quick response to user's actions
• Multi-user: distinction between users
• Network OS: users aware of the existence of multiple computers
• Distributed OS: looks like a traditional single-processor system

Basic Tasks Performed by OS

• Recognizing input from the keyboard
• Sending output to the display screen
• Keeping track of files and directories on the disk
• Controlling peripheral devices such as printers

Main Functions of an OS

• Process management: creates, schedules, and destroys processes
• Memory management: allocates and releases memory
• File management: creates, reads, modifies, and removes files
• Security
• Command interpretation

Process Management

• A process is a program in execution
• Process management manages the processes submitted to a system to minimize idle time of processors
• Process Management Mechanisms in Early Systems:
  • Manual loading mechanism: jobs were manually loaded one after another in a computer by the computer operator
  • Batch processing mechanism: batch of jobs was submitted together to the computer and job-to-job transition was done automatically by the operating system
  • Job Control Language (JCL): control statements were used to facilitate job loading and unloading

Memory Management

• Memory is an important resource of a computer system that must be properly managed for the overall system performance
• Memory management module:
  • Keeps track of parts of memory in use and parts not in use
  • Allocates memory to processes as needed and deallocates when no longer needed

File Management

• A file is a collection of related information
• Every file has a name, data, and attributes
• File's name uniquely identifies it in the system and is used by its users to access it
• File's data is its contents
• File's attributes contain information such as date & time of its creation, date & time of last access, date & time of last update, its current size, its protection features, etc.

File Access Methods and Operations

• File Access Methods:
  • Sequential access: information stored in a file can be accessed sequentially
  • Random access: information stored in a file can be accessed randomly
• File Operations:
  • Set of commands provided by an operating system to deal with files and their contents
  • Typical file operations include create, delete, open, close, read, write, seek, get attributes, set attributes, rename, and copy

Security

• Deals with protecting the various resources and information of a computer system against destruction and unauthorized access
• External security: deals with securing computer against external factors such as fires, floods, earthquakes, stolen disks/tapes, etc.

Learn about the file management module of an operating system, which involves structuring, accessing, naming, sharing, and protecting files. Explore two commonly supported file access methods: sequential access (accessing information in order) and random access (accessing information randomly).