Mr. Data seemed to be a very advanced and unique Android in Star Trek TNG.
It came to my attention, however, that (seemingly more advanced? or at least more humaniform) androids existed in the hundreds of thousands in Star Trek TOS.
The episode I'm referencing is "I, Mudd", (the title being a clever reference to Asimov's "I, Robot", much like the iPod and iPhone).
In light of this, did Data break any new ground as an android? Was his oft-malfunctioning emotion chip the only area where he (and his brother) represented an advance in robotics/cybernetics?