[cctalk] Re: undocumented instructions including HCF [was: System 360 question]

Not bricking, but breaking: From multicians.org: "The tape drives used on the GE-635 <https://www.multicians.org/mga.html#635> were some of the first self threading drives. As a result they needed an extremely long tape leader before the "reflector spot" and this was a pain for MIT operators <https://www.multicians.org/mgo.html#operator> when loading the tapes onto the IBM 7094 <https://www.multicians.org/mga.html#7094> running CTSS <https://www.multicians.org/mgc.html#CTSS>. Lee Varian <https://www.multicians.org/multicians.html#Varian> wrote some tricky code, and we put two load point reflectors on the tapes we shuttled between the 7094 and the 635. The 635 would only sense the farther-in load point; the 7094 would load to the early load point and then Lee's code would space it way out and rewind back to the 635 load point. If we didn't find the right label, his code tried three times and then deliberately broke the tape so the operator would have to put on new load points at the correct places. (You could break a tape on the '94 by putting it into high speed rewind and then doing a reset data channel command, I suppose it's safe to reveal this now.)" -- Charles X-Clacks-Overhead: GNU Terry Pratchett