FIFOs

A FIFO, or first-in, first-out, is a method for organizing data so that the oldest item added is the first to be processed or removed. FIFOs are used in computing as a principle for queues, buffers, and intercomponent communication, where preserving insertion order is important.

In computer science, a FIFO is typically implemented as a queue data structure. It supports operations such as enqueue (add to the end), dequeue (remove from the front), and peek (inspect the front element). Elements are processed in the exact order they were received. Implementations may use linked lists or arrays; fixed-capacity versions often employ circular buffers. Enqueue and dequeue operations are usually designed to be constant time, with memory usage proportional to the number of stored elements.

In hardware and digital design, a FIFO buffer decouples timing between producers and consumers. Hardware FIFOs use memory with separate read and write pointers and flags indicating full or empty status. They are common in data paths such as UARTs, USB controllers, network interfaces, and clock-domain crossings, where smooth data transfer between sampling rates or clocks is required.

In operating systems and interprocess communication, a FIFO can refer to a named pipe in Unix-like systems. Created with tools such as mkfifo, a named pipe provides a unidirectional channel (or two channels when paired) for data exchange between processes. Access is controlled by permissions, and reads or writes can block until the other side is ready, making it a simple synchronization mechanism.

Variants and considerations include circular buffers, lock-free queues for concurrent environments, and potential drawbacks such as head-of-line blocking or fixed capacity limits. Overall, FIFOs offer predictable ordering and straightforward semantics across software, hardware, and IPC contexts.