On 2017-Mar-05, at 11:27 AM, Chuck Guzis via cctalk wrote: > On 03/05/2017 10:41 AM, Mark J. Blair via cctalk wrote: >> >> So, was the write enable state latched at some point in the loading >> cycle on those drives? That surprises me, because I would have >> expected the write enable sensor to interrupt write current as >> combinatorial function on the drive, and/or pass sensor status up to >> the formatter a combinatorial signal. > > Yup. You loaded the tape, then bumped the "finger". As I mentioned, > this worked on 60x and 65x drives. Since the autoloaders closed the > door as part of the cycle, this probably didn't work for 66x. > > This actually worked pretty well--you never ran the risk of leaving a > ring in inadvertently. The consequence of forgetting to enable write > was usually far less dire than mistakenly writing to a tape that was > supposed to be read-only.
In my limited experience of drives, but I expect it's typical, the write enable is electro-mechanically latched: if the write ring is present at load, a solenoid is activated which pulls the sense finger further in to hold the finger off the write ring, so it won't be a friction and wear point while running. The solenoid is released at unload.
