Real tape drive densities

[CuriousMarc]

> So, apparently my NRZI 9 track drive has the density option included, and
I don't know if there were any other 200/556 bpi 9 track drives out there. 
> When we got the drive I had hoped it would be a 7 track drive, but it
isn't.
Now I finally get it. NRZI, 200, 556 and 800 densities, but in 9 track all
the time. That's weird. You'd think the lower densities would be for 7
track. Could it be that it is a read-only for 7 tracks at lower density, but
a read/write at 800 for 9 tracks? If you looked at the head you might be
able to confirm if it has a dual 7 track / 9 track head.
Marc