When we first heard about the Surface it was reportedly planned that they were going to release the device with a unibody magnesium-aluminum chassis, but apparently capacity limitations from their chassis makers have made them change their mind- at least according to a new rumor. The rumor claims that the company will instead use a magnesium chassis that uses MegVapor technology for surface treatment to allow the device to feature a similar exterior to a traditional metal chassis. The problem, is that this method has a lower yield rate that will greatly affect MS’ ability to mass produce the new tablet, or so the sources claim.
The sources say that Microsoft inquired at several metal chassis makers what their available capacity was, and it was revealed to these makers that the tablet orders could easily go up as high as five million units by the end of 2012, which prompted them to give up because of the lack of capacity.
Before taking this information to heart, keep in mind that this is a rumor and hasn’t in any way been confirmed by Microsoft. It is possible that it could be true, but at this point its hard to clearly say one way or another.[ source ]