In the Windows Installer world, people tend to categorize updates into three groups: major upgrades, minor upgrades, and small updates. The primary distinction between these groups is the size of the update, or in other words, the number of changes that will take place. Speaking at a high level, a major upgrade completely replaces the existing software with a new set of files, registry keys, and so on. By contrast, minor upgrades and small updates only replace some of the files and leave the rest as they are.
In this section, we'll discuss how to plan for an update. It's beneficial to do this from the start before you actually need to author an update. In some cases, if you haven't authored your original installer in a way that supports updates, you'll find the task much harder later on.