I was trying to figure out which Space war game that was - I never had access to a PDP-1 (sob) but had a game called Spacewar which ran on the 6809 (Dragon, or Tandy in the US) and one that (I think) had the same name which runs on the Osborne 1 luggable. I could power the thing up and check, but I haven't tried since I last moved house.

p.s. 7 correct, but I did guess the billion seconds answer