Why don't applications launch right after I boot WIndows?

Question

I have a few applications in my task bar on Windows 7.

Right after the machine boots, the task bar is unresponsive: When I move my mouse over an icon, nothing happens. Very shortly after boot however, it becomes responsive and highlights the icon under the cursor.

When I click an icon at that point (say, Chrome, or a game), it becomes outlined, as if it was running. However, the outline goes away after a second or two.

For a brief period of time, the clicked application actually will not launch, even though the icon was outlined for a bit.

A few seconds later, the outline of a clicked icon will go away just as before but the application will launch eventually. If I clicked the icon several times in this phase, it will even launch several times.

My question is: Why does Windows not start the application in that short time frame? Afterwards, why does the outline go away? Why does clicking the icon repeatedly launch the application several times where pressing the icon later just brings it to the foreground? Does Windows not know whether the application has started or not? Does the application crash if it was started before Windows has completed whatever it needs doing until it is really running?

Basically, what is happening in that time that makes Windows behave so strangely?

Answer 1

Not all Windows subsystems are operational at that point. So any applications that rely on those subsystems cannot begin yet. Most commonly, these are subsystems involved in networking (firewall, automatic address assignment, UPnP discovery) and security (anything that requires elevated privileges).

Answer 2

The machine is busy loading programs in the background and you're waiting in line to perform your clicks (usually waiting for disk access). These click actions are buffered and will be sent as soon as possible.

Clicking a taskbar icon when the program isn't open will cause it to open an instance of it. Since you clicked it multiple times before it got a chance to open the first one, you get one for each click you made when none were open.