Its to large to be a DF32 (10"x1/4"), 32k. Probably an RF08, 256k. DF32 picture at http://www.pdp8.net/dfds32/pics/df32diskorig.shtml?small. The later DF32's got rid of the optical sensor for disk rotation so may not have a band around the outside. They switched to a one shot off the data. Not sure what the RF08's did.