[TUHS] Research UNIX PDP 11/45

[Henry Bent]

On Mon, 17 Jul 2023 at 20:49, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:

>     > From: Henry Bent
>
>     > there will be a lengthy addendum shortly.
>
> The most useful thing is probably this:
>
>   https://minnie.tuhs.org/cgi-bin/utree.pl?file=V4/nsys/ken/low.s
>
> which lists exactly what was there; not only the types, but how many of
> each
> there are. This is from 'nsys', which is slightly before the actual V4, so
> it's quite early. 'low.s' is inherently machine-specific; i.e. different
> machines would share most kernel files identically, but _not_ this one -
> unless they had _absolutely identical_ device sets. So this one is
> _probably_
> the one from the /45 in picture.
>
> It shows:
>
>   RK11
>   RF11
>   PC11
>   TC11
>   TM11
>
>   1xKL11
>   12xDC11
>   1xDP11        (synchronous serial)
>   1xDN11        (dial-out asynch control)
>
>   1xDR11C       (parallel port to -11/20)
>   2xDC11        (Screw Works voice synthesizer)
>   1xDR11A       (voice response unit)
>   1xDR11C       (C/A/T typesetter)
>
> (Line printer, card reader and RP11 are commented out; more about the RP11
> in a later message.
>
>
> There's also this:
>
>   https://minnie.tuhs.org/cgi-bin/utree.pl?file=V4/nsys/ken/11-45
>
> which is a bit hard to interpret, but I think might list what's in each
> rack:
> the TC11, RK11 (early ones), RF11 and TM11 (early ones) were large custom
> wire-wrapped backplanes which bolted into the front or back of a 19 inch
> rack; this:
>
>   https://gunkies.org/wiki/RK11-C_disk_controller
>
> has an image of such an RK11. The "MOS 16-24" is probably a reference to an
> MS11:
>
>   https://gunkies.org/wiki/MS11_Semiconductor_Memory_System
>
> which had to mount in the CPU backplane. The "MM" entries are likely core
> memory units; probably MM11-K's:
>
>   https://gunkies.org/wiki/MM11-K_core_memory
>
> since they seem to be 4KW each. (Maybe MM11-E's or 'F's, though; those are
> also 4KW each.) I'm not sure what they "PL"s are - probably Plessey core?
> Anyway,it looks like the machine had 104KB total.
>
>
> This file:
>
>   https://minnie.tuhs.org/cgi-bin/utree.pl?file=V4/nsys/ken/conf.c
>
> lists all the types of devices on the machine. One oddity is that it lists
> two RK11's; but if you look at the RK11 driver:
>
>   https://minnie.tuhs.org/cgi-bin/utree.pl?file=V4/nsys/dmr/rk.c
>
> it's only set up to handle one physical controller. But there is this:
>
>   #define       JRK     1       /* temp */
>
>         if (bp->b_dev.d_major==JRK)
>                 d = bp->b_dev.d_minor;
>         else
>                 d = bp->b_blkno%3;
>
> so the two different major device entries appear to handle the same disks
> in
> different ways ("d = bp->b_blkno%3" will spread a virtual drive across
> three
> physical drives).
>
>
> Memory, it would have been hard to say (UNIX even then sized memory at
> start
> up) but then I found that '11-45' file. I also found a copy of the CACM
> version of the UNIX paper:
>
>   https://people.eecs.berkeley.edu/~brewer/cs262/unix.pdf
>
> which says the machine had 144KB (so they had added 40KB more at that
> point).
> (I seem to recall someone had scanned the SOSP version; I didn't save the
> pointer, but if someone knows where it is, it would be interesting to look,
> and see what it says - they seemed to update this paper on a regular basis
> -
> the copy included with V6 talks about the -11/70.)
>
> The system at that point had "a 1M byte fixed-head disk .. four moving-head
> disk drives which each provide 2.5M bytes on removable disk cartridges, and
> a single moving-head disk drive which uses removable 40M byte disk packs"
>
> The RS11 disks for the RF11 were 512KB, so either they'd added a second
> one,
> or switched to an RS04 (but that's a MASSBUS device). The big disk was an
> RP03 so they had added an RP11, which wasn't present earlier.
>
>         Noel
>

Noel,
Thank you very much for this thoroughly researched and documented
explanation.  I hope that it will be of use to others as well.

-Henry
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