According to the Star Trek TNG Bible, Data had quite a different background. He was still the second in command, but had a quite a different appearance:
[He] is an android so perfectly fabricated that only a skilled biologist would know he is not composed of normal flesh and blood.
Perhaps explaining his appearance in the picture above.
At the time of writing (23 March 1987), the 'Bible' indicated that the role of Data had yet to be cast. However, Dr Noonien Soong was not planned to be the original creator of Data! Instead, he was
manufactured by highly advanced (and never seen) aliens who intended him to serve as a repository of all the memories of a doomed Earth-Asian space colony.
Which fits in well with Dr Soong's Asian heritage and living on Omicron Theta for a time.
His abilities as an android, namely his computational abilities, appear to be the same as the final character; he is described as a "walking library". Although as Xantec points out in the below comment, his unfamiliarity with certain information (e.g. the phrase 'snoop' in Encounter at Farpoint) suggest his knowledge was a bit more limited. Now, this is pure conjecture, but possibly because if Data knew everything that was known by the Federation, it probably wouldn't help move the plot along.
The TNG Bible also describes how Data was found alone on the planet by Starfleet who were searching for the colonists etc. with a very similar story as we hear in the final version.
Data's lack of emotions aren't described in much detail though, although his enthusiasm to learn what it is like to become a human (note: not quite the same as to actually become a human or as close to it as he can) is similar.
