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Date: Wed, 15 Jan 2020 11:46:47 -0500 (EST)
From: jnc@mercury.lcs.mit.edu (Noel Chiappa)
Subject: Re: [TUHS] Spacewar at Bell Labs [ really paper tape readers and
 tangentially related things ]
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    > From: Clem Cole

    > So WD designs and builds a few LSI-11 as a sales demo of what you could
    > do
    > ...
    > he put it on the QBUS which DEC could not lock up because they did not
    > create it as WD had.

Wow! WD created the QBUS? Fascinating. I wonder if DEC made any changes to the
QBUS between the original demo WD boards and the first DEC ones? Are there any
documents about the WD original still extant, do you know?

(FWIW, it seems that whoever did the QBUS interrupt cycle had heard about the
metastability issues when using a flop to do the grant-passing arbitrations;
see here for more:

  https://gunkies.org/wiki/Bus_Arbitration_on_the_Unibus_and_QBUS#QBUS_Interrupts

DEC had previously bent themselves into knots trying to solve it on the UNIBUS:

  https://gunkies.org/wiki/M782_Interrupt_Control#Revisions

so it would be interesting to know if it was WD or DEC who did the DIN thing to
get rid of it on the QBUS.)

    Noel