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In article <20767@cup.portal.com> mmm@cup.portal.com (Mark Robert Thorson) writes:
>With regard to the pdp-11 and the -10, I recall a puzzling fact from the
>PDP-11 Peripherals Handbook.  Out of a large collection of peripheral products
>there was one which did not have "11" in its name.  This was the DL10
>Unibus window.  It was also unusual in that it might not return slave sync
>for a ridiculously long time, like 30 seconds.
>
>I know DEC-20's used 11/40's as front end machines.  Did they interface via
>a DL10?  Could someone briefly describe what services the 11/40 did?
>(Or it might have been labelled 11/35 -- same set of CPU cards.)

The DECSYSTEM-20 site prep documentation references the DL10, but only as
the terminal lines for a KL10.  There were really DH11's driven by the
11/40 front end.

All KL10's had an 11/40 front end; I suspect that's what most 11/40's ended
up being.  On the DECsystem-10 the front end was the console processor
responsible for booting and controlling the back end.  On the DECSYSTEM-20,
in addition to its console duties the front end controlled all the unit
record devices: terminals (DH11), lineprinters (LP20 - a Unibus peripheral
despite its name), and card reader (CD20).  I think that, like the ARPAnet
interface, the card punch and paper tape peripherals were on an I/O bus
driven directly by the back end; only machines with such esoteric devices
had back-end I/O busses.

The console 11/40 ran a hacked-up version of RSX-11 called RSX-20F.  There
was elaborate code for each CPU to "keep alive" the other via a watchdog
timer that would push the other CPU's boot button if it failed to keep it
up to date.  The very earliest KL10 systems used the field service
diagnostic monitor for the 11/40 called KLDCP.

KL10's could have up to three secondary 11/40 front ends called DN20's;
generally these were DECnet synchronous line controllers.

The KS10 used an 8080 for its console processor and had a Unibus adapter
(UBA) to interface to the Unibus.  It drove the peripherals directly with
no front end help, modulo the KMC11 being a front end for a DUP11 in
synchronous DECnet (the DN20's also used KMC11's to drive DUP11's; the
combination was called "KDP").

Mark Crispin / 6158 Lariat Loop NE / Bainbridge Island, WA 98110-2020
mrc@CAC.Washington.EDU / MRC@WSMR-SIMTEL20.Army.Mil / (206) 842-2385
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