Change control

Change control is the discipline around putting anything into a live mainframe environment. A change is raised, described, assessed for impact, tested, reviewed, approved, scheduled into a window, and implemented with a documented way of backing it out.

It exists because of what these systems carry. An error in a payments application is not a broken page; it is money moving incorrectly, at scale, with regulatory consequences. The cost of a slow process is much lower than the cost of an uncontrolled one.

In practice this shapes how developers work. Code moves through development, test and production libraries under the control of a change management tool rather than being copied by hand. Promotion between environments is recorded. Which version of a program is live, and who approved it, is auditable.

If you have come from a continuous deployment culture, the pace can feel heavy. The controls are proportionate to the consequences, and plenty of sites are steadily automating the mechanics while keeping the assurance the process provides.