Operating System Tutorial

Operating System Tutorial Types of Operating System Evolution of Operating System Functions of Operating System Operating System Properties Operating System Services Components of Operating System Needs of the Operating System

Operating Systems

Linux Operating System Unix Operating System Ubuntu Operating System Chrome Operating Systems Fedora Operating System MAC Operating System MS Windows Operating System Solaris Operating System Cooperative Operating System CorelDRAW Operating System CentOS FreeBSD Operating Systems Batch Operating System MS-DOS Operating System Commercial Mobile Operating Systems


Difference Between Multi-programming and Multitasking Difference between C-LOOK and C-SCAN Difference between Rotational Latency and Disk Assess Time Trap vs Interrupt Difference between C-SCAN and SSTF Difference between SCAN and FCFS Difference between Seek Time and Disk Access Time Difference between SSTF and LOOK Difference between Process and Program in the Operating System Difference between Protection and Security in Operating System

How To

How to implement Monitors using Semaphores How to Install a Different Operating System on a PC


What is Kernel and Types of Kernel What is DOS Operating System What is Thread and Types of Thread What is Process Scheduler and Process Queue What is Context Switching What is CPU Scheduling What is Producer-Consumer Problem What is Semaphore in Operating System Monitors in Operating System What is Deadlock What is Paging and Segmentation What is Demand Paging What is Virtual Memory What is a Long term Scheduler What is Page Replacement in Operating System What is BSR Mode What is Convoy Effect What is Job Sequencing in Operating System Why is it critical for the Scheduler to distinguish between I/O-bound and CPU-bound programs Why is there a Need for an Operating System


Process Management Process State Scheduling Algorithm FCFS (First-come-First-Serve) Scheduling SJF (Shortest Job First) Scheduling Round-Robin CPU Scheduling Priority Based Scheduling HRRN (Highest Response Ratio Next) Scheduling Process Synchronization Lock Variable Mechanism TSL Mechanism Turn Variable Mechanism Interested Variable Mechanism Deadlock Avoidance Strategies for Handling Deadlock Deadlock Prevention Deadlock Detection and Recovery Resource Allocation Graph Banker’s Algorithm in Operating System Fixed Partitioning and Dynamic Partitioning Partitioning Algorithms Disk Scheduling Algorithms FCFS and SSTF Disk Scheduling Algorithm SCAN and C-SCAN Disk Scheduling Algorithm Look and C-Look Disk Scheduling Algorithm File in Operating System File Access Methods in Operating System File Allocation Method Directory Structure in Operating System N-Step-SCAN Disk Scheduling Feedback Queue in Operating System Contiguous Memory Allocation in Operating System Real-time Operating System Starvation in Operating System Thrashing in Operating System 5 Goals of Operating System Advantages of Operating System Advantages of UNIX Operating System Bit Vector in Operating System Booting Process in Operating System Can a Computer Run Without the Operating System Dining Philosophers Problem in Operating System Free Space Management in Operating System Inter Process Communication in Operating System Swapping in Operating System Memory Management in Operating System Multiprogramming Operating System Multitasking Operating Systems Multi-user Operating Systems Non-Contiguous Memory Allocation in Operating System Page Table in Operating System Process Scheduling in Operating System Segmentation in Operating System Simple Structure in Operating System Single-User Operating System Two Phase Locking Protocol Advantages and Disadvantages of Operating System Arithmetic operations in binary number system Assemblers in the operating system Bakery Algorithm in Operating System Benefits of Ubuntu Operating System CPU Scheduling Criteria in Operating System Critical Section in Operating System Device Management in Operating System Linux Scheduler in Operating System Long Term Scheduler in Operating System Mutex in Operating System Operating System Failure Peterson's Solution in Operating System Privileged and Non-Privileged Instructions in Operating System Swapping in Operating System Types of Operating System Zombie and Orphan Process in Operating System 62-bit operating system Advantages and Disadvantages of Batch Operating System Boot Block and Bad Block in Operating System Contiguous and Non - Contiguous Memory Allocation in Operating System Control and Distribution Systems in Operations Management Control Program in Operating System Convergent Technologies in Operating System Convoy Effect in Operating System Copy Operating Systems to SSD Core Components of Operating System Core of UNIX Operating System Correct Value to return to the Operating System Corrupted Operating System Cos is Smart Card Operating System Cosmos Operating Systems Examples Generation of Operating System Hardware Solution in Operating System Process Control Block in Operating System Function of Kernel in Operating System Operating System Layers History of Debian Operating Systems Branches and Architecture of Debian Operating Systems Features and Packages of Debian Operating Systems Installation of Operating System on a New PC Organizational Structure and Development in Debian Operating Systems User Interface in Operating System Types Of Memory in OS Operating System in Nokia Multilevel Paging in OS Memory Mapping Techniques in OS Memory Layout of a Process in Operating System Hardware Protection in Operating System Functions of File Management in Operating System Core of Linux Operating System Cache Replacement Policy in Operating System Cache Line and Cache Size in Operating System What is Memory Mapping? Difference Between Network Operating System And Distributed Operating System What is the difference between a Hard link and a Soft Link? Principles of Preemptive Scheduling Process Scheduling Algorithms What is NOS? What is the Interrupt I/O Process? What is Time Sharing OS What is process termination? What is Time-Sharing Operating System What is Batch File File system manipulation What is Message-passing Technique in OS Logical Clock in Distributed System

Free Space Management in Operating System

What is Free Space Management?

The system always keeps the records of the free disks blocks for allocating space to files when they are created. To use the space free from removing the files, free space management becomes critical. The system maintains a free space list which keeps record of the disk blocks that are not assigned to some file or directory.

Free Space Management in Operating System

When file is created, operating system searches the free space register for saving the file. During deletion the file, the computer system frees the given space and attaches this to the “free space list”.

There are four methods used in the free space management of operating system. There are as follows:

  1. Bitmap or Bit vector
  2. Linked list
  3. Grouping
  4. Counting

Bitmap or Bit vector

A bitmap is a group of bits where each bit corresponds to a disk block. It can take two values: 0 and 1, where 0 indicates that the block is allocated and 1 indicates the free block. This is the most common method used to implement the free space list. In this method, each block in the hard disk is implemented by a bit.

Advantages of Bit vector

Advantages of bit vector are as follows:

  1. It is simple and easy to understand.
  2. It consumes less memory.
  3. It is well organized to find free space.

Disadvantages of Bit vector

Disadvantages of bit vector are as follows:

  1. OS goes through the all blocks unless it finds a free block.
  2. To find a free block, OS may need to search the entire bit vector.
  3. It requires a special hardware support in some conditions.

Linked list

In this method, the free disk blocks are attached together. A free block carries a pointer to the next free block. The block number of the very first disk block is collected at a separate location on disk and also cached in memory. This method has a major disadvantage that it requires for free space list traversal. This entire process is known as linked list.

Advantages of linked list

Advantages of linked list are as follows:

  1. In this method, accessible space is used effectively.
  2. As there is no size limit on a linked list, new space can be allocated easily.

Disadvantages of linked list

Disadvantages of linked list are as follows:

  1. In this method, the overhead of maintaining the pointer appears.
  2. The linked list is not efficient when we need to reach each block of the memory.


This is also an important method for free space management. In this method, there is a modification of free list takes place which stores the address of the n free blocks. In grouping, the initial n-1 blocks are free but the last block carries the address of n blocks. When we use the standard linked list, the address of the higher number of blocks can be found very quickly. In grouping, we cannot keep a list of n free disk addresses but we keep address the initial free block. This whole process is known as grouping.

Advantages of grouping

Advantages of grouping are as follows:

  1. The address of higher number of free blocks can be found very quickly.
  2. Grouping is a type of method which has a benefit of making it simple to locate the addresses of collection of empty disk blocks.
  3. The modification of free list takes place that’s why there is no need to pass over the whole list.

Disadvantages of grouping

Disadvantages of grouping are as follows:

  1. The major disadvantage of grouping method is that the space of block is wasted in storing addresses. Nth block is used to collect the addresses of next free blocks.
  2. Addresses of initial free blocks can be saved but we are not able to maintain the list of all n free disk addresses.
  3.  It is very costly in maintaining the index of blocks.


Here, counting is the last method of free space management in operating system. This method is also used in the modification of the linked list method. This method has an advantage most of contiguous blocks can be freed concurrently. In this type of method linked list is maintained as well as the pointer to the next free block that come after first block is also preserved. There is no need to traverse the whole list. This whole process is known as counting.

Advantages of counting

Advantages of counting are as follows:

  1. Fast allocation of higher number of consecutive free blocks.
  2. Random access to the free block can be performed.
  3. Entire list is generally smaller in size.

Disadvantages of counting

Disadvantages of counting are as follows:

  1. Every free block requires huge space to keep the count in the disk.
  2. To perform traversal operations, we have to store the entries in B-tree.
  3. Whole area got reduced in counting.