Comparison between a package manager and an installer
Criterion
Package manager
Installer
Shipped with
Usually, the operating system
Each computer program
Location of installation information
One central installation database
It is entirely at the discretion of the installer. It could be a file within the app's folder, or among the operating system's files and folders. At best, they may register themselves with an uninstallers list without exposing installation information.
There could be as many formats as the number of apps
Package format compatibility
Can be consumed as long as the package manager supports it. Either newer versions of the package manager keep supporting it or the user does not upgrade the package manager.
The installer is always compatible with its archive format, if it uses any. However, installers, like all computer programs, may be affected by software rot.