From Wired.com:

When the satellites we rely on for navigation can’t be reached — whether they’ve been jammed or you’re in a densely packed city — the chip contains everything you’ll need to figure out how to get from place to place. It’s got gyroscopes, accelerometers and a master clock, to calculate orientation, acceleration and time. The TIMU is fabricated from silicon dioxide and contained within a 10 cubic millimeter package — meaning it can just about fit within the Lincoln Memorial rendered on the back of a penny.