I've been trying to get my head around the TR1 addition known as aligned_storage. Whilst reading the following documents N2165, N3190 and N2140 I can't for the life of me see a statement where it clearly describes stack or heap nature of the memory being used. I've had a look at the implementation provided by msvc2010, boost and gcc they all provide a stack based solution centered around the use of a union. In short: Is the memory type (stack or heap) used by aligned_storage implementation defined or is it always meant to be stack based? and, What the is the specific document that defines/determines that?