Origin of 'blockbuster'?

[FrankU]

So why do we call a good film a blockbuster? Is it because it busts the block of DVD's in which it can be found in DVD rental shop?
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[Jamie (K)]

The other meaning of blockbuster is a huge aerial bomb that can destoy targets in a broad area. So when a blockbuster is released, it goes BOOM! and covers a wide area.

But oddly enough, if you call a movie a "bomb" in the US, it means it's a failure. I think in the UK it used to mean the film was a success, but I'm not the expert on UK vocabulary here.