FIFO

FIFO stands for First-In, First-Out. It describes a rule for handling sequences of items where the oldest item is processed or removed before newer ones.

In computer science, FIFO is a queue data structure where elements are enqueued at the rear and dequeued from the front. This policy ensures that requests are served in the order they arrive. Operations on a FIFO queue are typically O(1) for both enqueue and dequeue, and variations include circular buffers and concurrent, lock-free implementations. In operating systems, FIFO scheduling is a simple policy that serves processes in arrival order, though many systems combine it with other strategies to improve responsiveness (e.g., aging, priority-based schemes).

In hardware and networking, FIFO buffers store data in the order it arrives to decouple producers and consumers. They are implemented as memory with separate write and read pointers and are common in device interfaces, data paths, and communication protocols.

In accounting and inventory management, FIFO is a cost-flow assumption used to value inventory and calculate cost of goods sold. Under FIFO, the oldest inventory items are matched against revenue first, so the remaining inventory reflects newer costs. This can affect reported profitability and taxes, especially in times of rising prices, and is contrasted with LIFO and average-cost methods.

Overall, FIFO is a simple and widely used principle across computing, manufacturing, and finance. It favors predictability and logical order, but may have drawbacks in terms of efficiency or tax/financial outcomes depending on context.