Yep, they stored all the powder way below deck, under the belt of armor. They had a system that lifted it to the guns, the powder storage rooms in themselvs are massive, I almost got lost down there!
The range finding "computer" they used filled a large room, and was mostly mechanical. Really its amazing how accurite they could fire those things from a moving rolling ship. Remember when they were engaged with other ships they were not only at flank speed, but had to menuver to avoid whatever the other guy was sending there way.