Today, a common user deals with web applications, mobile applications, and desktop software. All of these are interactive, which means they take user input and respond in real time. They might not even be aware of other kinds of applications—applications that run in the background, do not need continuous user interaction, and may go on for hours, days, or even weeks! Yes, I am talking about the batch job that is typically used for offline processing such as file type conversions, reporting, data mining, and so on. In the early days, machines were too slow and someone had to sit for hours to get a simple job done. In batch processing, you submit jobs and then go and do other work—you only come to collect the result! This revolutionized the computing world and justified the exorbitantly high prices of equipment and programmers. It would not be an exaggeration to say that batch jobs showed the real power and usefulness of computers.

If batch jobs are...