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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 ma
by dboreham 4y ago
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.
- zh3 4y agoOh, 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?
- pinewurst 4y agoOut of TTL or FPGA?
- dboreham 4y agoAt 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 4y agoI 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 4y agoAlso should say that I am a digital design engineer from the 70's/80's so tackling this tech is not a problem per se, but the goal is more about time-travel -- re-creating the smell, sound, flashing front panel lights, heat and feeling of being in the room next to a multi-user pdp-11.
- dboreham 4y agoI have a complete set of cards pulled 20 years ago from a working system.
- kabdib 4y agoI knew a guy (Marc Crispin) who had a PDP-20 in his spare bedroom. His power bill was . . . large.
- dboreham 4y agoYeah an 11/70 needs 3-phase which I don't have.
- adrian_b 4y agoIt is more important if you have enough electrical power available. Building or buying a 3-phase inverter or a power supply unit that could replace the original power supply are much easier tasks than building the logic boards of PDP-11/70, which you have. If the power requirements exceed what is available at your location, you could still make the PDP-11/70 work for very short times, by using a large enough UPS with a 3-phase inverter or with a substitute power supply, and charging the UPS, then starting the PDP-11/70 with the UPS disconnected from mains. The power requirements can be reduced a lot in comparison with a real PDP-11/70 if only the processor boards are used and the memory boards are replaced by a modern FPGA board implementing the protocol of the DEC memory bus. The maximum size of the PDP-11 memory (4 MB) is small enough that it can be implemented with the internal SRAM of many FPGA chips, no external DRAM memory is needed.