Dangerous Hardware 2490

I'm a programmer, but I used to have to deal with a couple of Siemens 0777 laser printers (laserdrucken). They were very fast and printed on continuous forms paper (33 inches-second regardless of the lines-inch). The nozzles, jets and cutesy flappers and paddle wheels that tried to stack the paper back up at that speed were impressive enough, but the whole mess was driven by a hacked up Varian running a multi-tasking OS named Vortex (appropriately so as it really did suck ;-). This brings us to the main point, the tape drive.

The tape was covered by a transparent door that opened and closed at the whim of the machine. Tapes auto mounted so the door made an air-tight seal. The door was just big enough to put a full-size reel of tape on the hub. The hub had a handle in the center that you twisted 90 degrees to lock the tape onto the hub. It merely expanded the hub a bit until it snugged up in the tape. Now for the really fun part.

If you put the tape on and forgot to lock the hub, when you pushed the button, the door would go ahead and close with no warning about the hub being unlocked. Apparently a sensor of some sort would have cost too much money. Once the tape door closed, the hub would start turning and, naturally, the tape would start to turn in the same direction, ok so far. Then when the drive reeled out enough tape for the auto threader to pick it up, the hub would stop. Of course the tape continued to turn and the drive sensed tape moving too far, so it naturally began to turn the hub the other way. Well, inertia is an amazing thing and it seems that the firmware in the drive just couldn't quite grasp what was happening. It would then rapidly try to rewind the tape and then retry the threading process. This cycle would continue with things moving faster and faster until the hub was spinning back and forth at full speed. Then (without fail) the tape drive would cause the tape to slide between the tape and the reel containing it. It would then perfectly wrap three turns of tape around the innermost part of the tape reel hub without so much as stretching the tape one bit. Of course you could never pull the tape back out by hand without destroying it, so your dataset was pretty much trashed at this point.

This was not really dangerous per se, but I can't tell you how awful the feeling is when you push the button and the door starts to close and just then you realize that you forgot to lock the hub. :-O