I just graduated from DM, coming back for a fourth year in CS. I've had a generic Windows laptop for all three years and didn't really have a problem. In first year, I did all coursework in the DCS computer labs on their Linux machines (surrounded by coursemates also doing their Java "robot maze"/"witter" courseworks). Second and third years I did most of the work on aforementioned Windows laptop and didn't have too many issues. It's likely that Macs will be harder to use, and in my opinion are more expensive for worse hardware but either way you can do courseworks 24/7 (a few long nights were had) in the computer labs on-site.