Servers are generally depicted as either a square computer hard disc as we know them from stationary computers, or large, square boxes with smaller square discs inserted (Which also looks a lot like a stationary computer). I wish there was some cool story behind their look, but there isn't. That's just how they look.
I've only recently gotten to know databases. How they work, SQL and the different scripts you can use. I love it. I think it's so much fun going into different databases when testing, viewing, comparing, joining and editing them. Even though the amount of trouble you can cause in there is immense.