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- Rotates only by fixed amounts, and controlled by a sequence of digital outputs.
- Stepper motors typically (for bipolar steppers) have 4 wires, two each for adjacent coils.
- Other, more complicated drive patterns such as full-step drive (two phases on), half-stepping etc. possible.
- Step angles of 1.8o, 3.6o, 7.2o etc. are typical.
- Positioning is relative - you can make it move by a certain angle (certain number of steps x step angle) from the current position. This is unlike servo motors which do absolute positioning where you don't need to know the current position to control the final position).
Courtesy 
A page with good explanation and figures : https://howtomechatronics.com/how-it-works/electrical-engineering/stepper-motor/
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