[HN Gopher] Building the PiDP-11 Dec PDP-11 Replica Minicomputer
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Building the PiDP-11 Dec PDP-11 Replica Minicomputer
Author : ecliptik
Score : 29 points
Date : 2022-11-23 18:35 UTC (4 hours ago)
(HTM) web link (bigdanzblog.wordpress.com)
(TXT) w3m dump (bigdanzblog.wordpress.com)
| lalalandland wrote:
| This computer looks so cool. The colors, the switches, the lights
| :-)
| watsocd wrote:
| The best I could find was a Dhrystone Benchmark of about 800MIPS
| for the PDP11/70.
|
| The Raspberry PI3 is rated 2,411MIPS.
|
| This emulator must be much faster than the original PDP11 even
| with the emulation software.
| zh3 wrote:
| 800MIPS? Not off an 11/70, for sure - much, much slower than
| that. 11/23's were as fast (or faster, depending on options and
| application) and they were maybe a single MIP or so (still got
| a couple of PDP11's kicking about, every so often I fire them
| up just to check my hearing).
| bdavis__ wrote:
| From memory.
|
| (The original) VAX 11/780 was a 1 MIPS machine. 32 Bit.
|
| pdp 11 was a slower machine. plus it was 16 bit. slow clock,
| a relatively cheap o'scope could be used to snoop the buses.
| zh3 wrote:
| Indeed, back in the day we bolted QBus backplanes to the
| side of DIN41612 backplanes and wire-wrapped across to a
| bunch of boards each with 100+ TTL chips on them (the 5V
| PSUs were something like 120A). The bus clocked at around a
| MHz, hence loosely the instruction rate (and back then, the
| addressed memory or peripheral needed to ack the bus cycle
| or there'd be a bus fault).
| timonoko wrote:
| 50 cent ESP-8266 would make excellent PDP-11. Except much
| too much memory. And 20 times too fast.
| williamDafoe wrote:
| The original PDP-11/70 was 0.7 vax mips. So it was 70% as
| fast as a Vax 11/780. I believe (from memory) the Vax
| 11/780 could do ~1757 dhrystone 2.1 mips so a PDP-11/70
| would be about 1230 dhrystone mips.
| https://wiki.cdot.senecacollege.ca/wiki/Dhrystone_howto
| dboreham wrote:
| I'm trying to build a _real_ pdp-11 /70. Mentioning the project
| to people I work recently with I realized that pretty much nobody
| knows the significance of this machine now. So perhaps worthwhile
| mentioning that it's the computer that the developers of the
| later versions of Unix used (by later I mean V6,7). It's also the
| target machine for Unix prior to the 1980s. Unix on an '11 is
| basically the ancestor of all the systems we use today. e.g. you
| could sit down at a terminal and you'd have familiar commands
| like cd, ls, grep, and you could to a first approximation get
| work done, write and compile C programs and so on.
| pinewurst wrote:
| Out of TTL or FPGA?
| dboreham wrote:
| At one time I did think about creating one from TTL, but I
| have a set of original cards now so probably easiest to just
| use those, either by building or buying a backplane and
| associated PSU.
| adrian_b wrote:
| I do not know if by "build" you mean building from scratch a
| real PDP-11, or just repairing an old real PDP-11, or just
| building an accurate emulator.
|
| Most real PDP-11 from the later years of the seventies had
| processors made with bipolar bit-slice circuits from the AMD
| 2900 series and memories made with 16 kbit chips like Mostek
| 4116 and these had to be supported by a large number of MSI and
| SSI Schottky TTL integrated circuits.
|
| Maybe a few such ancient integrated circuits in working state
| could still be found, but for a complete PDP-11 a very large
| number is needed (a 256 kB memory needs 128 DRAM chips, the
| maximum 4 MB memory needs 2048 DRAM chips, the CPU might need
| 40 to 100 bipolar logic chips). I do not believe that
| attempting to reproduce the large size and the great power
| consumption of a real PDP-11 can provide an improved self-
| teaching experience in comparison with the implementation of a
| clock-cycle-accurate emulator of PDP-11/70 on a modern FPGA
| board.
| dboreham wrote:
| I have a complete set of cards pulled 20 years ago from a
| working system.
| zh3 wrote:
| Oh, I think quite a few people do (plenty of PDP11 programmers
| about). It's easy enough to fire up an emulator and run a C
| compiler like its 1978 (or Fortran, come to that).
|
| What's the definition of 'real' here?
| mikewarot wrote:
| At Rose-Hulman they had a PDP-11/70 running RSTS that they had
| modified to have more than 128 terminals connected to. It's my
| understanding that it had 128K of RAM, and 144 terminals at one
| point circa 1982.
| musicale wrote:
| Kind of amazing the sort of functionality that old
| multiuser/timesharing systems were able to deliver. 128K
| (words, presumably) of RAM seems a bit low though for 128+
| users.
| musicale wrote:
| Nice but I'd prefer an FPGA implementation. ;-)
| smackeyacky wrote:
| The RetroBytes guy on Youtube has a (slightly annoying) video
| featuring this kit. If I had the time it would be a fun project.
|
| https://www.youtube.com/watch?v=bQUeMyAMQwo&ab_channel=Retro...
| musicale wrote:
| Original source of the PiDP kit that is being built:
|
| https://obsolescence.wixsite.com/obsolescence/pidp-11
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(page generated 2022-11-23 23:01 UTC)