A README in the root of 2.11 says:
The following manual pages are NOT in 2.10BSD but ARE in 4.3BSD:
and one of them is drum.4
so, I guess we need to look at a 4.3BSD system to find out what
drum they are talking about. I have a feeling this is a device
that works on the VAX but is actually not found on any PDP-11.
Why it automatically makes the device node is beyond me.
bill