Ralf Groene and his design team at Microsoft first conceived of the recently revealed Surface Book while working on the Surface Pro. Like the Pro, the Surface Book would function as either a laptop or a tablet. But, significantly, the new Book would be a laptop *first—*not a tablet with a kickstand. “We had the idea of people starting out with that laptop architecture, going about their business, and then transforming it into something more personal,” Groene says.

That insight won Microsoft a lot of love yesterday, but Groene, who serves as creative director on the Surface, wanted what he calls “clipboard mode”—i.e. tablet mode—to be great. And great, in this context, has a lot to do with screen size, processor size, and battery life. Groene didn’t want to compromise on any of those, which led to a structural engineering dilemma: To convert into clipboard mode, the display would need to balance at the edge of the keyboard base. But to do that, and do it sturdily, the base would need to be bigger than the display, which would add considerably to the device's weight.

Enter the hinge. Or, as Microsoft dubbed it, the dynamic fulcrum hinge. The connective tissue between the Surface Book’s base and display is an isopod-like piece of aluminum that flexes back and forth thanks to four rotational points. It’s “almost like a carpet that rolls out,” Groene says.

When Microsoft unveiled the Surface Book, it also unveiled the dynamic fulcrum hinge. It's a unique and arresting design created by the design team to make the Book flip easily from laptop mode to tablet mode. The Surface Book's keyboard detaches. The muscle wire lock allows the display to seamlessly lock onto the keyboard base. A button activates that component, which is made of a nitinol, a metal that contracts when it comes into contact with an electrical charge. The hinge allows the footprint of the base to extend by up to 20-millimeters on an as-needed basis. It has a stronger center of gravity for it, which meant the design team could shave off hundreds of grams in weight.

The hinge solved Microsoft’s structural problems by allowing the footprint of the base to extend by up to 20-millimeters on an as-needed basis. Making the Surface Book a little malleable worked, giving the device balance while allowing Groene and his team to shave off “hundreds of grams” in weight.

The hinge works adjacent to, but not directly with, the muscle wire lock, which allows the display to seamlessly lock onto the keyboard base. A button activates that component, which is made of a nitinol, a metal that contracts when it comes into contact with an electrical charge. This secures the Surface Book while in laptop mode. It’s built just outside of the hinge, and didn’t play a role in determining how the hinge was built, Groene says.

Fully realized, the hinge looks like a bit of a bling on an otherwise spartan PC. This is due in part to the fact that the hinge is aluminum, and the rest of the Surface Book is magnesium, which weighs around one-third less than aluminum. But the contrast in appearance, Groene says, is mostly accidental. “Our whole focus was to make the hinge be the hinge, and roll out, and save weight,” he says. “Concentrating on what the function should be almost suggests what the form should be, so we ended up with these different sections nesting together.” Groene even likens the final design to a folio, for how it elegantly rolls over onto itself. Again, that was all coincidental.

"The whole thing is pure function," Groene says. As we've said elsewhere, the Surface Book is a "laptop to spit fire." The hinge is one of the muscles making that possible.