By hang he just means it will run slow, freeze or crash I think. And that it often happens because the computer needs more RAM.
But perhaps we should discuss SimCity some more instead.
Eeehhh... What are your largest cities called? How many inhabitants do they have?
My record is "Ul Torv" with about 1.3 million inhabitants, but it was in 2005 where I later lost my data... Which has happened twice. But now it's running on my laptop where Noxium is the largest city, with a little more than 70,000 inhabitants.