DEC VT20 boot device

Paul Birkel pbirkel at
Sat Aug 10 13:56:48 CDT 2019

The DEC VT20 terminal apparently included a PDP-11/05 with a direct mapped
character display and was intended for text editing and typesetting.  It
seems to have been followed by the VT21, and then VT71/VT72, all three based
on an LSI-11 (KD11-F).  There's a real lack of documentation about these
online, although the VT72 does have a print set.


Apparently the VT20 used the M792-YK as its bootstrap; the Field Guide is
silent regarding the boot device and M792 documentation stops earlier in the
series of variants.


According to the VT72 print set, it used the MRV11-VC (M9942-YC; described
in the Field Guide as a "bootstrap/diagnostic module") for its bootstrap but
is also silent regarding the boot device.  In interestingly, the Field Guide
also describes a MRV11-AA (M7942-TB) as a "M7942 with VT52 emulator, VT71


For async. communications the VT20 used a DL11-B (M7800 (EIA)). the VT72 a
DLV11-F (M8028).


Looking in a DEC "Options and Modules" listing I see VT20 bundles including
Typeset-11 and DECset-11, and it appears that the VT20 could be configured
with two displays & serial lines in a single 11/05.


So . is the boot device in these systems the remote host via the serial
line?  What protocol would that have been?  Something native to Typeset-11
and DECset-11?



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