Based on the color scheme and component description, the bicycle is a 1988 model 712.

There is no signifigance to a numerical versus written model designation, other than the whims of the designer. The practice varied depending on the year and there were even some years where both formats were used. The number does however indicate the type of bicycle and relative position in the line-up. In this case it's a mid-range competition/fitness model.

To answer Top506, yes the frame is Miyata's excellent STB tubeset for the main triangle and fork. The stays are CrMo too. Save for the slightly less aggressive geometry and non-spline chainstays, the frame is pretty much the equivalent of a Team Miyata.

Shimano 105 is original and based on Miyata tires, it's a good bet that it's entirely original. At that price, it was a verey good deal. I don't have the original price, but based on similar models it should have been in the range of $500-$600US. FYI, claimed weight is 23.5 lb and the correct color designations is black and peacock. Please PM with your serial number and I will add it to my database.