Use application while it is installing

Question

I was installing the Office 2016 Preview yesterday (link for anyone who's interested) and noticed that you can actually use the Office applications provided before the installation is complete.

When running the Office applications while the installer is still running, I sometimes see a message in the bottom right corner explaining that Office is streaming required files. I also noticed that, when running Word somewhat early in the installation (according to the installer) and trying to open the Settings dialogue, Word would hang until it had streamed the files.

How would this installation system actually work? I've never noticed it on any other applications before.

Answer 1

multiplayer games do it more frequently. What happens is basically the following:

1. a streaming installer gets installed. This is a stub that does all the rest.
2. the absolute minimum to use the core functionality is installed. For Word (for example) that'd be opening and saving files, and some editing functionality
3. As you work, more functionality is installed. This is prioritised based on what you're actually using as well as common usage patterns (iow the installer predicts what you're going to need next and installs that first). You will therefore sometimes notice a "please wait" indicator while things are downloading that you're trying to use
4. eventually everything is installed and the installer stub deactivates. It may for example turn into an automated updater instead.

First time I encountered this was actually close to 10 years ago playing World of Warcraft, which works exactly like this.
Initially only the login and character creation functionality are installed. As you work through account creation, logging in, and character creation it installs the first levels/scenes of the game itself. While you're playing through those it installs ever higher levels, which will take you ever longer to get to so it doesn't matter that they're not available right away.