Glossary · System coordination, integration and orchestration
First in, first out (FIFO)
Also known as: FIFO, first come, first served
German: First In, First Out (FIFO)
In computing and production logistics, first in, first out (FIFO) is an ordering principle in which items are processed or removed in the same order in which they arrived, so that the oldest item is always handled next.
- System integration
In one sentence
First in, first out handles items in arrival order, so the oldest item in a queue, buffer or stock is always processed next.
Example
A PLC FIFO buffer stores the IDs of parts entering the oven, and the part leaving the oven is matched to the oldest ID in the buffer.
How it applies
- Control software: FIFO buffers track parts through conveyors and process stations. If a part is removed manually, the buffer and the physical sequence diverge; tracking logic needs a way to detect and correct this.
- Logistics: FIFO stock rotation reduces the risk of aged material, which matters for materials with shelf life. Some materials need first expired, first out instead.
- Documentation: Operating instructions should tell operators how to handle parts removed from or added to a tracked FIFO sequence. Interface documents should state whether messages or orders are processed in FIFO order.
FIFO vs. LIFO
Last in, first out (LIFO) processes the newest item first, as in a stack. FIFO preserves order and age; LIFO does not, and in a buffer can leave old items unprocessed for a long time.