Magtape write rings [Was: Re: Full immersion emulation]

Chuck Guzis cclist at
Sun Mar 5 13:27:19 CST 2017

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.


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