What Is a FIFO Data Structure?


Heather Bennett

A FIFO (First-In-First-Out) data structure is a type of collection where the first element added is the first one to be removed. It follows the principle of “first come, first served.” In other words, the element that has been in the collection for the longest time is the one that gets removed first.

How does a FIFO data structure work?
In a FIFO data structure, new elements are added to the end of the collection, and removal happens from the front. This behavior resembles a queue or waiting line, where people join at one end and leave from the other end.

Imagine a queue at a ticket counter. As people arrive, they join at the back of the line (enqueue operation).

When it’s time to purchase tickets, they are served from the front (dequeue operation). The person who arrived first will be served first.

Advantages of using a FIFO data structure:

  • Simple implementation: The FIFO concept is intuitive and easy to understand.
  • Efficient insertion and removal: Adding an element to the end or removing an element from the front can be done in constant time.
  • Natural order preservation: Elements are processed in their arrival order, which can be desirable in many scenarios.

Common use cases:

  • Task scheduling: When multiple tasks need to be executed in a specific order.
  • Message queues: Communication systems where messages should be processed in sequence.
  • Caching algorithms: In some caching strategies, older or less frequently accessed items are evicted first based on their arrival order.


A common comparison for understanding FIFO is with another popular data structure called LIFO (Last-In-First-Out). While FIFO follows a first-in-first-out order, LIFO operates on a last-in-first-out principle.

In a LIFO data structure, the most recently added element is the first one to be removed. It is similar to a stack of plates, where you can only remove the top plate. When new plates are added, they are placed on top of the stack.

Key differences between FIFO and LIFO:

  • Order of removal: In FIFO, the oldest element is removed first; in LIFO, it’s the most recently added.
  • Operation names: In FIFO, we use enqueue and dequeue; in LIFO, we use push and pop.
  • Data structure types: FIFO is commonly implemented using queues; LIFO is implemented using stacks.

Implementing a FIFO data structure in code

In many programming languages, you can implement a FIFO data structure using built-in data structures or by creating custom classes. One common approach is to use an array or a linked list.

Here is an example implementation of a simple FIFO queue using an array in Python:

class Queue:
def __init__(self):
self.items = []

def enqueue(self, item):

def dequeue(self):
if not self.is_empty():
return self.pop(0)

def is_empty(self):
return len(self.items) == 0

def size(self):
return len(self.items)

In this example code, elements are enqueued by appending them to the end of the list (`enqueue` operation) and dequeued by removing the first element (`dequeue` operation).


A FIFO data structure follows a simple rule: the first element added is the first one to be removed. It ensures that elements are processed in the order of their arrival. FIFO is widely used in various applications like task scheduling, message queues, and caching algorithms.

Remember, understanding different data structures and their characteristics is essential for solving real-world problems efficiently. So, make sure to grasp the concepts of FIFO and other data structures to become a better programmer.

With this knowledge, you can now confidently use a FIFO data structure to manage your collections effectively!

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