I know of people that put two drives in their Mac book pros but there is a catch. Since there is limited room you have to use a kit to install it in your drive bay so if you use your drive you will then need to use it as and external drive. I don't see any reason you couldn't do this with an iMac. I would, however, rather have two ssd drives and an external super drive. I don't like traveling with an external hd, they don't hold up that well for me.

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