[TUHS] /dev/drum

Warner Losh imp at bsdimp.com
Sat Apr 21 02:33:04 AEST 2018

On Fri, Apr 20, 2018 at 10:12 AM, Dan Cross <crossd at gmail.com> wrote:

> That's a bit different. It's possible that some early Unix machines had
> actual drum devices for storage or swap (did any of them?), but the
> /dev/drum device is what Clem says it was.
> It's funny, I just happened across this a couple of days ago when I went
> looking for the `hier.7` man page from 4.4BSD-Lite2:
> https://www.freebsd.org/cgi/man.cgi?query=hier&apropos=0&
> sektion=7&manpath=4.4BSD+Lite2&arch=default&format=html
> It refers to this: https://www.freebsd.org/cgi/man.cgi?query=drum&
> sektion=4&apropos=0&manpath=4.4BSD+Lite2
> The claim is that it came from 3.0BSD. Why was it called drum? I imagine
> that's historical license coupled with grad student imagination, but I'm
> curious if it has origin in actual hardware used at UC Berkeley. Clem, that
> was roughly your era, was it not?


So there's something called drum in 3BSD. Haven't chased down the MAKEDEV
and config glue to turn it into /dev/drum, but it's enough to support the
'It originated in 3BSD'. It certainly wasn't in 32V since that had no

This was 1980. Drum memory stopped being a new thing in the early 70's. So
it was just recently obsolete. But its typical use was a very small, but
very fast, hard drive to swap things to. There never was a drum device, at
least a commercial, non-lab experiment, for the VAXen. They all swapped to
spinning disks by then.


        - Dan C.
> On Fri, Apr 20, 2018 at 12:00 PM, David Collantes <david at collantes.us>
> wrote:
>> I found a Wikipedia[0] entry for it.
>> [0] https://en.m.wikipedia.org/wiki/Drum_memory
>> <https://en.m.wikipedia.org/wiki/Drum_memory?wprov=sfti1>
>> --
>> David Collantes
>> +1-407-484-7171
>> On Apr 20, 2018, at 11:02, Tim Bradshaw <tfb at tfeb.org> wrote:
>> I am sure I remember a machine which had this (which would have been
>> running a BSD 4.2 port).  Is my memory right, and what was it for
>> (something related to swap?)?
>> It is stupidly hard to search for (or, alternatively, there are just no
>> hits and the memory is false).
>> --tim
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