Fly by wire focusing
'Fly by wire' is a technical term for the real time physical control of a mechanical operation without a direct mechanical link. Instead, analogue or digital signals transmitted by wire are acted on by an electro-mechanical control mechanism. Fly by wire operates a mechanism as if it were mechanically controlled although there is no mechanical connection.
Olympus included fly by wire lens focusing with all its Four Thirds lenses when the E-System was launched in 2003. When the manual focus ring is operated, its movement is sensed by the camera body and the corresponding action is transmitted electronically to the focus servo motor system to move the focus in real time. This is why, when the electrical pins and/or contacts at the lens mount are dirty - manual focusing can become defective.
As there is no mechanical connection between the manual focus ring and the focus mechanism, the construction of the lens can be simplified, mechanically. Manual focus control can also be effected from a computer if desired (although it's not clear if this was ever implemented).
A drawback of fly by wire manual focusing is that there is no physical limit to the rotation of the focus ring to determine where closest focus or infinity lies.