The Always-Present Spirit

The Day of Pentecost commemorates the event recorded in Acts 2, where 120 followers of Jesus were baptized in the Holy Spirit. But as we contemplate this event and the four similar ones recorded in Acts, and then consider what Jesus had to say about the giving of the Spirit, it begs the question: what was the Holy Spirit doing before the Day of Pentecost? Did they just hang out in heaven before it was time to show up? Or was the Spirit there all the time and people were just slow to realize that?