MacBook 5,1 was made of Aluminum?

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Browsing through the OWC install videos I just noticed that MacBook 5,1 seems to be made of Aluminum (unibody). I know the earlier MacBook were made of polycarbonate and later models, unibody, also of polycarbonate material, but I was not aware that there was a model (5,1), in fact 2 revisions of basic MacBook (not PRO) made of unibody Aluminum. Interesting.

http://www.everymac.com/systems/apple/ma...specs.html