Thanks for the reply: This bike was advertised on the local internet bulletin board yesterday as a give-away so it cost me nothing and it was dirty but rideable. All it need was air in the tires. The seat was white (!) so I put on a black seat. Kids are so very into mountain bikes these days that the old-fashioned ones get thrown out.

Early 80s, I suspect. Everything on the bike has "Shimano AX" or "Altus AX" written in cursive script on it, including the Shimano AX brake levers, flat Adamas AX cast aluminum pedals and both Altus AX derailleurs. And the centre-pull brake cables are hidden. The bike actually feels quite good.

Wiki sez: In the 1980-1983 period, Shimano introduced two groupsets with "AX" technology: Dura-ace and 600. Features of these components include aerodynamic styling, centre-pull brakes, brake levers with concealed cables, and ergonomic pedals.