For sale 128K Core RAM Industrial PDP 11/40 Massbus System

Noel Chiappa jnc at
Mon Oct 31 10:06:10 CDT 2016

    > From: Allison

    > Later versions like 2.9 and V7 do want I&D.

V7 is only distributed with pre-built loads for split I+D machines (so you
can't boot a V7 distribution tape on a non-split machine), but it includes
machine-language OS support files for non-split machines. (It's similar
enough to V6 that it makes sense that it runs on non-split machines.)

    > From: William Degnan

    > Given 128K core, wouldn't one be able to save the OS in core, no need
    > to load what would need to "get started" from a diskpak?

To fork a process, Unix swaps the forking process out, and then fiddles
system tables so that one of the two copies (I forget which, without looking
at the code) becomes the child. This includes at startup, when the 'swapping'
process (0) splits and the child (1) is set up to run /etc/init. (I
found this out the hard way, when bringing up V6 under Ersatz-11. :-)

So Unix won't run without a swapping device.


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