Thus it is analogous to the behaviour of persons queueing (or "standing in line", in common American parlance), where the persons leave the queue in the order they arrive, or waiting one's turn at a traffic control signal. FCFS is also the shorthand name (see Jargon and acronym) for the FIFO operating system scheduling algorithm, which gives every process CPU time in the order they come. In the broader sense, the abstraction LIFO, or Last-In-First-Out is the opposite of the abstraction FIFO organization, the difference perhaps is clearest with considering the less commonly used synonym of LIFO, FILO—meaning First-In-Last-Out. In essence, both are specific cases of a more generalized list (which could be accessed anywhere). The difference is not in the list (data), but in the rules for accessing the content. One sub-type adds to one end, and takes off from the other, its opposite takes and puts things only on one end.
A priority queue is a variation on the queue which does not qualify for the name FIFO, because it is not accurately descriptive of that data structure's behavior. Queueing theory encompasses the more general concept of queue, as well as interactions between strict-FIFO queues.
Authors and users of FIFO queue software should consider carefully the use of the terms "head" and "tail" to refer to the two ends of the queue. To many people, items should enter a queue at the tail, remain in the queue until they reach the head and leave the queue from there. This point of view is justified by analogy with queues of people waiting for some kind of service and parallels the use of "front" and "back" in the above example. Other people, however, believe that you enter a queue at the head and leave at the tail, in the manner of food passing through a snake. Queues written in that way appear in places that might be considered authoritative, such as the GNU/Linux operating system, making the point of view hard to dismiss however repugnant you find the idea of getting your data from a snake's rear-end.
A synchronous FIFO is a FIFO where the same clock is used for both reading and writing. An asynchronous FIFO uses different clocks for reading and writing. Asynchronous FIFOs introduce metastability issues...... A common implementation of an asynchronous FIFO uses a Gray code (or any unit distance code) for the read and write pointers to ensure reliable flag generation. One further note concerning flag generation is that one must necessarily use pointer arithmetic to generate flags for asynchronous FIFO implementations. Conversely, one may use either a "leaky bucket" approach or pointer arithmetic to generate flags in synchronous FIFO implementations.
Examples of FIFO status flags include: full, empty, almost full, or almost empty.........
The first known FIFO implemented in electronics is done by Peter Alfke in 1969 at Fairchild Semiconductors. Peter Alfke is now a Director at Xilinx......
Read and write addresses are initially both at the first memory location and the FIFO queue is Empty.FIFO Empty: When read address register reaches to write address register, the FIFO triggers the Empty signal.FIFO FULL: When write address register reaches to read address register, the FIFO triggers the FULL signal.