iMovie has "events" and "projects". The events contains all the video clips. The projects contain iMovie instructions on how to build the movie from the clips. The movie only actually exists as a entity when you export it. Once you do that you can view it anywhere. If you don't export, then you need to copy both the event clips and projects between the systems and view from iMovie, which must be the same version. I often capture video and create projects on my MacBook and then complete the processing and export on my iMac (which is much faster). I create about 2 hours of video a week. But I always create .MOV files for viewing.