[TUHS] /dev/drum

Clem Cole clemc at ccc.com
Tue Apr 24 07:06:23 AEST 2018

On Mon, Apr 23, 2018 at 4:47 PM, Grant Taylor via TUHS <tuhs at minnie.tuhs.org
> wrote:

> On 04/23/2018 11:51 AM, Clem Cole wrote:
>> By the time of 4.X, the RP06 was 'partitioned' into 'rings' (some
>> overlapping).  The 'a' partition was root, the 'b' was swap and one fo the
>> others was the rest.  Later the 'c' was a short form for copying the entire
>> disk.
> I had always wondered where Solaris (SunOS) got it's use of the different
> slices, including the slice that was the entire disk from.
> Now I'm guessing Solaris got it from SunOS which got it from 4.x BSD

​It was not BSD - it was research.  It may have been in 6th, but it was
definitely in 7th.  Cut/pasted from the V7 PDP-11 rp(4) man page:


rp − RP-11/RP03 moving-head disk


The files rp0 ... rp7 refer to sections of RP disk drive 0. The files rp8
... rp15 refer to drive 1 etc. This

allows a large disk to be broken up into more manageable pieces.

The origin and size of the pseudo-disks on each drive are as follows:

disk start length

0 0 81000

1 0 5000

2 5000 2000

3 7000 74000

4-7 unassigned

Thus rp0 covers the whole drive, while rp1, rp2, rp3 can serve usefully as
a root, swap, and mounted user

file system respectively.

The rp files access the disk via the system’s normal buffering mechanism
and may be read and written

without regard to physical disk records. There is also a ‘raw’ interface
which provides for direct transmission

between the disk and the user’s read or write buffer. A single read or
write call results in exactly one

I/O operation and therefore raw I/O is considerably more efficient when
many words are transmitted. The

names of the raw RP files begin with rrp and end with a number which
selects the same disk section as the

corresponding rp file.

In raw I/O the buffer must begin on a word boundary.​

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