If you scroll the map the first time there will be some HD access, as it loads the graphics. And of course if you process a turn. But aside of this there shouldn't be too much work on the HD needed. Be sure that you have enough free mem (which should be the case with 2.5 GB
) and that you enabled the option 'Use high mem' (or something like that).
But frankly speaking I never monitored the HD access while playing, but I will watch the little lamp next time.