Complex sentence: This was at first intended for traditional magnetic and optical drives, but has been extended to support a wide variety of devices, particularly flash drives, because many systems can be controlled with the familiar metaphor of file manipulation within directories.
Split into simpler sentences: This was at first intended for traditional magnetic and optical drives and has been extended to support flash drives. It has also been extended to support a wide variety of novel devices as many systems can be controlled with the familiar metaphor of file manipulation within directories.