Early file system layouts (/ and /usr split)

Warren Toomey wkt at cs.adfa.edu.au
Thu Apr 13 15:32:02 AEST 2000

[ This came to me from a NetBSD mailing list, via Greg Lehey ]

Someone said.....
> >>> Did you not know that /usr was split off only because the disks were too
> >>> small to keep everything on one way back in the early days

Someone else said....
> > I believe that the topic of splitting / and /usr was discussed
> > at the Glasgow University meeting of the UKUUG, which was around
> > 1978, if my memory serves me well. As the first copy of V5 and V6
> > came out of the labs in the 1975/1976 timeframe, I suspect it came
> > later. I don't have my copy of the CACM paper to hand, so I can't
> > check dates.

The answer is: UNIX had / and /usr split by at least the time of the
July 1974 CACM paper ``The UNIX Time-sharing system''.

Here is the evidence:

At http://minnie.cs.adfa.edu.au/PUPS/Images/ken-and-den.txt and

you will find a picture of Ken and Dennis at the PDP-11/20 around 1972.
The commentary in the text file from John Holden tell us that the disk
drives are RF-11 and RK03 drives.

RF-11 drives were fixed head drives with 512K of storage with fast access.
RK03s and RK05s could store 2M, but were not as fast as RF-11s.

The source code to (nearly) 3rd Edition UNIX, dated August 31, 1973, only
has drivers for two disks, RF-11s and RK05s. This source code is in the
PUPS Archive, http://minnie.cs.adfa.edu.au/PUPS. You need a Unix src license.

Now, the July 1974 CACM paper says this:

	In our installation, for example, the root directory resides
	on the fixed-head disk, and the large disk drive, which contains
	user's files, is mounted by the system initialization program; ....

To me, this strongly indicates that / and /usr were split by at least
July 1974, if not the earlier date of August 1973.

Cheers all,

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