Well, the electronic ignition didn't show up until the 1981 models. There were fully faired 800cc and 1000cc bikes during the '81-'84 time frame along with dual disks. A third disk was available in the rear, but IMO that's a waste of time...a drum brake probably works better. The '81 to '84 bike were also prone to poor valve seat metallurgy with limited heat transfer, which resulted in the need for a valve job sooner rather than later. Beginning in 1985, BMW fixed that. There were twin shock models through 1984, but with the 1981 models, a monolever came out in the R80G/S and R80ST. These have more of an off-road nature to them.

Starting with '85-on, only monolevers were available and the paralever came in later in the '80s IIRC.

If you want to look at specs of various bikes, check out this site:

http://www.bmbikes.co.uk/bmwmodels.htm

The Mystic series near the end of production were something of a throwback and tried to capture some of the earlier styling.