A servo is an automatic device that uses error-sensing feedback to correct the performance of a mechanism. The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position or other parameters.

A common type of servo provides position control . Servos are commonly electrical using an electric motor as the primary means of creating mechanical force . Usually, servos operate on the principle of negative feedback , where the control input is compared to the actual position of the mechanical system as measured by some sort of transducer at the output. Any difference between the actual and wanted values (an "error signal") is amplified and used to drive the system in the direction necessary to reduce or eliminate the error.

Feedback from the motor is typically via encoders or less commonly resolvers. However, with a motion control system, there may be multiple position inputs that govern the commands sent to the motors. One example is in precision linear positioning, where position data may be collected from linear scales, optical detection of load position and so forth. Indeed, one of Delta Tau's strengths in this field is the ability to handle large amounts of positional data in near real-time – thereby delivering machine builders not just accuracy, but also speed.

Servo motion was once the domain only of precision machinery such as machine tools and packaging machines. However, price reductions and a simplification of the motor controls has seen the use of servo technology extend somewhat. For example, many autofocus cameras also use a servomechanism to accurately move the lens, and thus adjust the focus. A modern hard disk drive has a magnetic servo system with sub-micron positioning accuracy.

Typical servos give a rotary (angular) output. Linear types are common as well, using a screw thread or a linear motor to give linear motion.

In industrial machines, servos are used to perform complex motion and come in both AC and DC variants. Delta Tau controls are fundamentally suited to both AC and DC servo motor control.