Components

The basic building block of an MSI is the component. Windows Installer doesn’t just install components but it manages them. It will track how many applications use a component and prevent them from being removed it it’s shared and used by other applications. Windows Installer also performs validation checks on the components every time an application is used. When Windows Installer heals an application it’s because it is checking each of the components to see if they appear damaged or altered.

The component is the smallest divisible unit when creating an MSI. It may contain a combination of files, registry keys or shortcuts. To adhere to Microsoft’s rules for creating components, all resources (files, shortcuts, registry keys) that reference each other directly should be grouped within a single component. That means that registry keys that point to doe within a particular DLL (known as COM entries) should be grouped in the same component as that particular file.

There can be instances when a component has more than one file. This is fine as long as none of the files contain COM entries. As a general rule, every DLL,.EXE or OCX should reside in it’s own component.