Build request pending for too long

Hi

We have two project areas sharing the same build server and a single build engine running on that server. The server and build engine is created by/in the other project area.

In the other project area's build queue, I see one build is running and the other pending. In my project area's queue, I see my build is pending.

1. I can see all build definitions in both project area, but I can't see that build engine created in the other project area, why?

2. Why there are two queues, one in the other project area and another in my project area? In what sequence the build engine is pulling the requests?

3. Is build engine single threaded? Why can't process requests at the same time?

Thanks
Jirong