Apple first announced the iPhone 4's gyroscope at WWDC 2010, but it was largely overshadowed by other big players inside the phone -- the A4 processor, Retina display, and external antennas. A lot of technology gets stuffed into vibrational gyroscopes (the type found in the iPhone 4), yet a casual observer may barely notice the chip itself, let alone the phenomenal contents within it. iFixit and Chipworks have partnered to show you exactly what's inside these little gems:
According to Wikipedia's definition, "A gyroscope is a device for measuring or maintaining orientation, based on the principles of conservation of angular momentum." The key phrase is measuring or maintaining orientation, which is the exact reason an iPhone 4 contains one of these gizmos.