What Is First In, First Out FIFO Data Structure?


Heather Bennett

FIFO, which stands for First In, First Out, is a fundamental data structure used in computer science and programming. It follows the principle that the first item to be inserted into the data structure will be the first one to be removed. In other words, it operates on a “first come, first served” basis.

Understanding FIFO

FIFO is often compared to a queue in real-life scenarios. Just like how people form a line at a ticket counter or at the supermarket checkout, FIFO works similarly with data elements. The first element that enters the queue will be the first one to leave.

Let’s imagine a scenario where you want to implement a print spooler program. The program needs to manage multiple print jobs and ensure that they are printed in the order they were received. This is where FIFO comes into play.

Operations in FIFO

FIFO supports two main operations:

  • Enqueue: This operation adds an element to the end of the queue. The newly added element becomes the last element in the queue.
  • Dequeue: This operation removes and returns the front element from the queue. The second element becomes the new front.

The enqueue operation increases the size of the FIFO, while dequeue decreases it by removing an element from the front.

The Structure of FIFO

In programming, FIFO can be implemented using various data structures such as arrays and linked lists. The choice of implementation depends on factors like performance requirements and ease of use.

FIFO using Arrays

In this implementation, an array is used as a container for holding elements. The front variable keeps track of the index of the first element, and the rear variable keeps track of the index of the last element in the queue.

The enqueue operation involves incrementing the rear variable and adding the element at that index. The dequeue operation increments the front variable to remove and return the element at that index.

FIFO using Linked Lists

In this implementation, a linked list is used to create a FIFO data structure. Each node in the linked list holds an element and a reference to the next node. The front pointer points to the first node, while the rear pointer points to the last node.

The enqueue operation involves creating a new node, setting its value, and updating the next reference of the current rear node to point to this new node. The dequeue operation updates the front pointer to point to the next node and returns the value of the current front node.

Benefits of FIFO

FIFO has several advantages:

  • Order Preservation: FIFO ensures that elements are processed in their original order, making it ideal for scenarios where order matters.
  • Simplicity: FIFO is relatively easy to understand and implement compared to other complex data structures.
  • Efficiency: Enqueue and dequeue operations can be performed in constant time complexity (O(1)), making it efficient for managing large amounts of data.

Real-World Applications

FIFO finds applications in various domains:

  • Print Spooling: As mentioned earlier, print spoolers use FIFO to manage print jobs in order.
  • CPU Scheduling: Operating systems often use FIFO as a scheduling algorithm for managing processes in the order they arrive.
  • Buffer Management: In networking, FIFO is used to manage data packets in routers and switches.


FIFO, or First In, First Out, is a simple yet powerful data structure that follows the principle of processing elements in the order they are received. It provides a fair and efficient way of managing data by ensuring that the first element to enter is the first one to leave. Understanding FIFO and its implementation using arrays or linked lists can greatly benefit programmers in various real-world scenarios.

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