Batch window

The batch window is the time available for overnight processing. It opens when the day's online activity dies down and closes when the business needs its systems ready again, and everything in between has to fit.

This is one of the defining pressures of mainframe operations. A bank might have a few hours to apply a day of transactions, calculate interest, produce statements, run regulatory reporting and prepare files for other institutions, with branches opening at a fixed time regardless of how it went.

Two things make the window shrink. Business volumes grow, so the same work takes longer. And organisations increasingly expect services to be available around the clock, which cuts the quiet period the window depends on.

That pressure explains a great deal of how batch is designed: why jobs are broken into restartable steps, why dependencies are mapped precisely so unrelated work runs in parallel, and why a single job overrunning is treated seriously. Someone is usually watching the clock against the window all night.