2 Mar
2022
2 Mar
'22
8:15 a.m.
On Tue, Mar 1, 2022, 6:23 PM Noel Chiappa <jnc(a)mercury.lcs.mit.edu> wrote:
You made a comment that MINI-UNIX wasn't available outside of Bell... I
meant to say that the AUUG newsletters talk about it. It features a letter
asking for users of it to share patches. There was also an article about
how to get it, though it was an offer to spin a tape for a photocopy of you
Western Electric license...
Warner
I'm not now sure how much memory my -11 _did_ have initially, but it's not
From: Andrew
Hume
the actual configuration of Lions; PDP 11/40 was
128 Kbytes of core memory
...
but note that because ... of addressing weirdness (the top 8KB were
memory-mapped to I/O registers), Lions' PDP actually had 112KB of
main
memory
I think that '112KB' must be an error; the 8KB for the 'I/O page' (as
DEC
eventually named ir, long after the rest of the world had started using the
term :-) were deducted from the _UNIBUS_ address space, meaning a UNIBUS
-11
(the 'pure' UNIBUS -11's, i.e. other than the -11/70, -11/44, etc) could
have
a maximum of 248KB of main memory (which is on the UNIBUS).
A pure UNIBUS -11 with 128KB of main memory (like Lions') has... 128KB of
main memory. The 'small memory management model' -11's (like the /40,
/60,
/23, etc) can use at most 64KB of that _at any moment in time_ for user
processes (i.e. directly accessible by the CPU, in 'user' mode).
(The kernel on such machines is basically retricted to 56KB at any moment
in
time, since one 'segment/page' - the terminology changed over time - has
to be
dedicated to the I/O page: the memory management control registers are in
that, so once the CPU can no longer 'see' them, it's stuck. Long,
potentially
interesting digression about, and ways to semi-work around that, elided,
unless people want to hear it.)
From: Noel Chiappa
The -11/40 (as it was at first) that I had at LCS
had, to start with,
I'm pretty sure, 3 MM11-L units .. - i.e. 48KB. I know this sounds
incredible, and I'm having a hard time believing it myself, wondering
if my memory is failing with age
It is:
# size /lib/c0
13440+2728+10390=26558 (63676)
('c1' takes 14848+6950+2088=23886, FWIW.) So 'my' -11/40 must have
had more
than 48KB.
MINI-UNIX provides, on an -11/05 type machine with the maximum of 56KB of
addressable main memory (if you plugged in 64KB worth, the /05 CPU couldn't
'see' the top 8KB of that), up to 32KB for a user process. So that will
just hold the stock V6 C compiler.
important.
Noel