PDP-12 at the RICM

Noel Chiappa jnc at mercury.lcs.mit.edu
Tue Jul 14 07:13:40 CDT 2015

    > From: Rich Alderson

    > Changing from PDP-8 operation to LINC operation was a matter of a
    > physical switch.

Err, not according to the "Small Computer Handbook" (1967 Edition), which
covers the LINC-8 in detail - at least, as I understand it? See, for instance,
pg. 307 "A LINC HALT instruction will also stop the LINC and return control to
the PDP-8." And see also the "Operational Summary", pp. 308-309, and Chapter
7, "LINC - PDP-8 Intercommunication".

Reading the handbook, it _seems_ like, in theory at least, the two machines
could run simultaneously (albeit contending for memory bandwidth), although
the canonical programming approach was to have one pause while the other
ran. Or perhaps that supposition is incorrect, and the two couldn't correctly
deal with contention for memory (although the LINC used the standard PDP-8
'data break' mechanism for access to memory, which was used by DMA devices
such as disks, so the -8 should have been able to deal with it; perhaps the
LINC couldn't); or perhaps there was some vital piece of circuitry shared by

I wonder if any LINC-8's still exist?

    > "PDP-8/i + LINC hybrid"

The bone I have with that description (which may be technically correct) is
that it implies that prior to the PDP-12, there were only the two separate
machines (PDP-8 and LINC).

But I know I'm a stickler for small details... :-)


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