Ramadan - Is this equality and why is it like this?

in virtually all mosques I have ever seen there is normally a separate room for women that is either upstairs, downstairs or behind the main room. The main room is normally the room men use and is normally the room most accessible from the main entrance to the mosque. In most British large mosques the main room is the one under the dome and the most beautiful, the women's room is much smaller and often only accessible by the stairs or back entrance. If women are equal to men in Islam why is it like this? Also, why can't women and men be in the same room but with a divider down the middle or something like that? I have seen that in ONE mosque, a Salafi one, but they changed it back after a short while.