I know it seems overly simple, since it is already in the lesson plan, but I plan on opening this up by using the journal entry to get the discussion started. I have always found that once kids have had a chance to get some of their ideas down on paper, they are much more likely to participate in a group discussion.
I will use that as the first step in a think-pair-share activity. Once students have had a chance to think about what they consider a computer and write it down, I will then have the share it with their elbow partner. Once everyone has had a chance to get some validation from another student, I will then ask for people who would like to share their ideas with the whole class in order to start a class discussion.