In aircraft instruments, gyros are used in attitude, compass and turn coordinators. These instruments contain a wheel or rotor rotating at a high RPM which gives it two important properties: rigidity and precession. The rotor or gyro can be electrically or vacuum / pressure driven by a separate pump on the engine.
In our current modern times, these old school large mechanical, heavy gyro's are now being replaced with new small sized Micro ElectroMechanical Systems aka MEMS. You will find these in Attitude and Heading Reference Systems (AHRS) for detecting acceleration and thus aircraft movement in three axis.
These devices are based on microscopically small vibrating structures packaged similar to integrated circuits and able to provide digital and or analog outputs. Most of them contain several sensors for multiple axis, ie X, Y and Z. They are used extensively in aviation, automotive and small personal devices like smartphones and such.
Micro electromechanical systems is a technology developed around 1986, that can be defined as miniaturized mechanical and electromechanical components (i.e., devices and structures) that are made using the techniques of microfabrication much the same as integrated circuits are created with lithography. MEMS devices are made up of small structures with sizes between 1 to 100 micrometers (i.e. 0,001 to 0,1 mm).
Our MEMS devices generally generally sit in the range from 20 micrometers to a millimeter (i.e. 0,02 to 1,0 mm).
The types of MEMS devices can vary from relatively simple structures having no moving elements, to extremely complex electromechanical systems with multiple moving elements under the control of integrated microelectronics. The one main criterion of MEMS is that there are at least some elements having some sort of mechanical functionality, whether or not these elements can move.
The term used to define MEMS in different parts of the world may vary. They are mostly called MEMS in the United States, while in other parts of the world they go by the name "Microsystems Technology" or "Micromachined Devices".
While the functional elements of MEMS are minuscule structures, sensors, actuators, and microelectronics, the most remarkable (and probably the most interesting) elements are the micro-sensors and micro-actuators. Micro-sensors and micro-actuators are appropriately categorized as "transducers". They are are defined as devices that convert energy from one form to another. In the case of micro-sensors, the device typically converts a measured mechanical signal into an usable electrical signal. And this can be further processed for eventual display in an EFIS system.
Nano ElectroMechanical Systems (NEMS) are even smaller than MEMS and contain very small sensors, actuators and even opto and acoustical components. See image above for an example of a such an actuator.
An AHRS (Attitude and Heading Reference System) provides three dimensional orientation by integrating gyroscopes and combining this data with accelerometer data and magnetometer data. With sensor fusion, drift from the gyroscopes integration is compensated for by reference vectors, namely gravity and the magnetic field of the Earth.
This results in a virtually drift-free orientation, making an AHRS a much more cost effective solution than conventional high-grade IMUs (Inertial Measurement Units) which only integrate gyroscopes and must rely on a very high bias-stability of the gyroscopes.
Most manufacturers of EFIS systems supply an AHRS in one form of another with their system.