[TUHS] Memory on Lion's v6
andrew at humeweb.com
Tue Mar 1 09:27:04 AEST 2022
the actual configuration of Lions’ PDP 11/40 was
128 Kbytes of core memory,
a DJ11 terminal multiplexor and
three RK05 disc units each,
but note that because of the way the machines were bought,
and because of addressing weirdness (the top 8KB were memory-mapped to I/O registers),
Lions’ PDP actually had 112KB of main memory.
the PDP 11/40 had 18bits of address space, so while processes were limited
to 64KB, the system could have had 256KB.
> On Feb 28, 2022, at 7:48 AM, Clem Cole <clemc at ccc.com> wrote:
> On Mon, Feb 28, 2022 at 12:51 AM Will Senn <will.senn at gmail.com <mailto:will.senn at gmail.com>> wrote:
> Does anybody know how much memory was configured on the PDP-11 that Lion's used for the commentary system. Here's what the book says about the system:
> ; from lions, page 1
> ; The code selection presumes a "model" system consisting of:
> ; PDP11/40 processor;
> ; RK05 disk drives;
> ; LP11 line printer;
> ; PC11 paper tape reader/punch;
> ; KL11 terminal interface.
> I usually add the mag tape, too
> ; TM10 magnetic tape - not in lions, but super handy
> It seems like he must have had an MMU and 128k memory, but I don't know. I'm hoping y'all remember, know, or can otherwise divine the correct value. I've run with no MMU - crash on boot. I've also run with less memory, but then cc won't build mkconf, when I have the TM10 enabled kernel loaded. As a reminder, his book was published in 1977.
> Can't tell you definitively. You'd need to ask some one like Andrew.
> FWIW: the 11/40 has a MMU, but does not support split I/D like the 45. He has 256K bytes [128k words] as the Max memory. IIRC v6 will boot with 48K words [96K bytes] - maybe a little less. But the less physical memory, the slower the system (the more it swaps).
> DEC was just switching to semiconductor memory at the time and it was pretty expensive. The MS11-B was MOS based 18 bit x 4K word modules for the 11/45, which were dual ported Unibus and Fastbus. I have forgotten what the 11/40 used as we tended not to use DEC memory modules***.
> Lions and his team was likely to have been between 96K and 256K max, depending on budget. In my experience, we tended to build up to max memory on systems, but only as soon as we could afford it. In my experience, we often bought the machines in phases... just enough to boot it, with two or three RK05's to start. Then add more memory and more serial ports and more terminals. Then more (larger) disk and maybe a tape drive and printer, and then even more serial ports and some sort of modems and network connections.
> *** At CMU during those days, we tended to use aftermarket memory or locally designed memory boards on the 11/40 and 11/34s as EE/CS had negociate and bought a few megabytes of memory chips from National Semi for C.mmp at a heavy discount - other groups could add to that order as needed.
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