I was not able to get access to any of my notes to more completely answer Eric's question. Short answer: NO. Otrona did not have two different obscure numbers of tracks for their disk sides. On the limited number of Otronas that I encountered. What I encountered was very straight-forward WD-like ordinarty disk formats. IIRC, they were 10 sectors per track, with 512 bytes per sector. There were 40 cylinder and 80 cylinder. There was a CP/M, and an MS-DOS. I don't remember what the distribution of those formats was, although I specifically remember a 96tpi (800k) MS-DOS. Ironically, the first one that I saw was a doctor at a hospital. To flog the point about portability, Otrona did an early ad with a Chaplin imitator trying to carry a card table with a PC on it down steps in front of a building (capitol?) IBM claimed to own Chaplin (and did apparently pay royalties to Chaplin estate), although Chaplin himself was not a big fan of biug corporation. I wasn't able to answer more fully, nor even now. I just spent a week in the hospital. giant kidney stone and massive infection. First few days were intolerable levels of pain. I am now on 2 weeks of 24/7 IV antibiotic infusions. Bizarre little pump that I carry around, but, at least I'm carrying it around at home, instead of the hospital. THEN, in 2 weeks? they will operate to try to remove the stone. They are hoping to do it with trans-urethral laser, with lithotripsy as a fall back. I had not prepared for being in the hospital, so only had a phone (Samsung Galaxy S4), and it wasn't until the third day that I was able to wrangel access to my pants (and pocket contents) I think that I will recover. THANK YOU to the folk who wrote to me with good wishes! -- Grumpy Ol' Fred cisin at xenosoft.com