TRS-80 curiosity

[Bill Gunshannon]

So, I just picked up an MISE from Bartlett Labs (cause I really liked
the M3SE I had) and decided to revive one of my TRS-80 MOdel I's.
In my box of "stuff" I found an interesting ribbon cable the function
of which I don't know.  It is a 40 pin to 50 pin ribbon cable with a
black box connecting them that is labeled TANDY.  I know of nothing
the Tandy made that used a 50 pin connector other than a hard disk.
Could that be what this is for?  Anybody ever seen one?  I no longer
have any Tandy External HD's but then, with things like MISE and FreHD
why would one still want one other than for nostalgia.

bill