> there is no definition for a rst device; the only tape entity is the tz*
> family.


this is correct. When you do MAKEDEV tz0 you will get the st devices. (st,
rst, nrst, and so on) 
tz is trhe dirver in the kernel. the st names are the device names in
/dev, which are nothign but convention. you could call the device file
/dev/hamburger as long as the major/minor was right. the major/minor
numbers indicate what device and what driver in the kernel to use. MAKEDEV
only helps you by keepign a database of the common names for these devices
and what the major/minors should be, and then calls mknod with the right
arguments to make the file for you. 

isildur