Each process will have a certain amount of work to do. This may be a short job, like processing a key press, or a long job such as calculating PI to a million decimal places. The SJF will try and process short jobs before longer jobs. The idea being that short jobs tend to be user interface related. If these are delayed for too long then the computer may become less responsive.

When a job gets eneterd into the ready to run queue it will be placed based on the amount of time it needs to run. Longer jobs will be placed at the end while shorter jobs will be placed at the start.