Toad1 XKL version of TOPS20 v7

Rich Alderson cc at
Tue Sep 21 17:27:22 CDT 2021

> Date: Tue, 21 Sep 2021 15:26:43 -0400
> From: Bob Smith via cctalk <cctalk at>

> I have noted that the Computer History Museum has a number of donations from
> XKL re Toad1.

Look again.  That system, the documentation, and the backup tapes, were donated
by HEWLETT-PACKARD CORPORATION, not by XKL.  Tim Litt was responsible for this
donation, probably to keep ev erything from simply being binned by the HP folks.

> Rich Alderson might be the resident expert for this set of questions.

Quite likely. ;->

> two questions are thus prompted, and a third teased.
> 1. Does that XKL version run on the KLH10 emulator?

Absolutely not.

KLH10 emulates a KL-10 processor with Massbus peripherals, which is what Ken
Harrenstien was interested in doing.  Neither he, nor the late Mark Crispin
after he took over maintenance on KLH10, had access to Toad-1 internals.

Major differences between the two processors:

    1.  The XKL-1 CPU (and all follow-on processors) implement the full 30-bit
    	extended addressing defined for release 4 of TOPS-20 by DEC.  The KL-10
    	implements a 23-bit subset.
    2.	In conjunction with this, the XMG-1 memory card provides 32MW of
    	memory, contrasted with the physical maximum of 4MW in the KL-10.
    3.	The XRH-1 I/O processor implements 4 FASTWIDE SCSI-2 channels (top of
    	the line in 1995 when the system was introduced), rather than Massbus.
    4.	The XNI-1 Ethernet board implements 4 10baseT interfaces compatible
    	with the Stanford MEIS rather than the DEC NIA-20.
    5.  The backplane of the Toad-1 system implements a completely different
    	model of inter-card interactions than the KL-10, so that so-called "I/O
    	instructions" are completely different from those of the KL-10.  They
    	resemble, but are unrelated in detail to, the I/O instructions on the
    	KS-10 processor in the DECSYSTEM-2020.

With all these differences, there is no way for KLH10 to even begin to execute
the XKL version of the TOPS-20 monitor.

> 2. Is the tape CHM has been archived anywhere it might be available
> for download?

That's a question for Al Kossow, rather than for me, since I was never
associated with CHM other than as an admirer.

> and the teaser
> 3. Has anyone created an SSH Server for TOPS20?

Not to my knowledge, although it has been attempted several times.

Although it has not been fully set up yet, AFAIK, the folks at have
just acquired an XKL DarkStar box in the TOPS-20 engine configuration, and will
be moving from a KLH-10 emulation to actual PDP-10 hardware in the very near
future.  This is a TOAD-2, like those run by LCM+L for the last few years of
its operation.


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