FIFO: First-In, First-Out


A FIFO queue is a queue that operates on the first-in, first-out principle, hence the name. This is also referred to as the first-come, first-served principle.

In other words, FIFO queueing is when customers are served in the exact order in which they arrive.

FIFO is the most common type of queueing, and it is generally believed to be the fairest way to manage queues.


Examples of FIFO queueing in real life

Most queues that we encounter throughout the day are FIFO queues. Waiting for the bus, waiting in front of the elevator or a vending machine, or even standing in line to the bathroom all share one quality — the person standing in the front goes before the one standing behind.


First-come, first-served in restaurants

You could say that restaurants, cafes, and fast-food chains operate on a first-come, first-seated basis. If a restaurant is particularly popular, there may be a line of soon-to-be-customers at the entrance, with the staff guiding the people to the newly available tables.

The earlier you got in the queue, the sooner you get the table.


First-in, first-out queues in banks

Banks are also notorious examples of FIFO queueing. There is either a separate queue for different tellers, or there’s one queue, and the customers at the front get served by whichever teller is available at the moment.


Whatever the service method they use, the principle is the same: the earlier you come, the sooner you get to resolve your issue.



Why use FIFO queueing?

Let us look at the core benefits of first-in, first-out queue management.


FIFO queueing promotes fairness.

First-in, first-out is inherently a very simple, easily understood principle. This makes FIFO fair in the eyes of customers: the earlier you join the queue, the sooner you get served.

There are no shortcuts or jumping ahead within FIFO rules. Fairness of queues is directly to customer satisfaction.


FIFO queues take advantage of the psychology of queueing.

This is connected with the previous point, as the perception of wait times is influenced by the fairness of the queue we stand in.
Knowing that the queue operates on the first-come, first-served basis alleviates the anxiety.




Naturally, there is more to the world of managing queues than FIFO. There are other systems that we encounter in different industries or social contexts.


LIFO: Last-in, first-out 

Also called last-come, first served (or LCFS, but that is less punchy than LIFO), the exact opposite of FIFO sounds absurd at first.


You come in last, but you get served ahead of the others?

Last-in, first-out is relevant for systems which have stacks of items/orders placed on top of each other.

The problem with a regular queue where you serve first those who arrive first is that people tend to arrive too early.


LIFO, on the other hand, forces people to come at staggered times, resulting in shorter queues. Coming early poses more risks.

Obviously, this system was not quite popular with the people who have been queueing the longest. Also, LIFO was subject to gaming the system, as some people left the queue and re-joined it from the back to get served more quickly.




Priority queueing is exactly what it says on the cover: customers have priorities associated with them and are served in the order prescribed by these priority classes.


This type of queueing is most seen in industries where there can be emergency cases — for example, healthcare. There is a difference between a patient with mild symptoms versus a victim of a near-fatal accident.

The latter is always treated before the former, as the level of urgency is that much higher.


Priority queueing is also reserved for VIP customers. Business class passengers enter the airplane before the rest, and people of importance may get seated at a restaurant ahead of anyone else.

It may feel unfair to reward fewer patient customers with faster resolution time, but for some companies, the risk of getting a negative review outweighs all potential consequences.




Not everything is as clear-cut as FIFO or LIFO.
Sometimes waiting line management takes elements from different types of queueing systems. To illustrate this point, we will once again invoke the food industry.


In restaurants and fast-food chains, if you make the same order as the person who came before you, there is a chance you will both receive your order simultaneously.

That is because it is easier to prepare certain meals in bulk: instead of making two servings of gazpacho separately, a cook will just prepare a bigger portion at once and distribute it to two customers.

Those are the unwritten rules of queueing in restaurants. The people who have been waiting longer than you may act grumpy, but they understand the logic behind you getting served ahead of them.



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