There was also an RK08, as I recall -- same platter as
the RK11/RK05 but 16 sectors per track instead of 12.
I thought the RK(0)8 was the controller for a PDP8 system. I have an RK8E in my PDP8/E,
it links to
a normal RK05 drive.
It does indeed use 16 (hard) sector packs, unlike the 12 sector ones used in the same RK05
drives
linked to an RK11 controller (RK11C, RK11D, RKV11D) on a PDP11.
The HP7900 drive uses the same type of cartridge but 24 sector.
-tony