I had an r c a recorder bought in 1963 that used a much larger version of 
the cassette.  I don't recall what they were called, but the same 
principle.  It had a metal frame you could use and play standard 3 inch 
reels if you wanted, but the recordinc surface was toward the outside as 
it is in casettes.  Those cartridges were probably 4 by 6 or close to 
that.
73
Butch
WA0VJR
Node 3148
Wallace, ks.