PiDP-11 and Pi Zero 2 W - recent experiences?

[Hugh Fisher]

Hello everyone - I'm new to the group. My PiDP-11 replica ships on Monday. Does anyone have recent experience running their replica, or even just running SIMH, on a Pi Zero 2 W?  Starting out, my use case is to run it headless and play with BSD 2.11 and ancient Unix over VNC (Wi-Fi). 

I've got a couple of Pi 4s here that I'm using for other things, but I can pick up a 512MB Zero 2 W for $15 at Micro Center, so wanted to consider that as an option first.

Thanks!

[sunnybo...@gmail.com]

I just rebuilt my PiDP-11 system after the SD died after many years. I'm using a Pi 3B+, latest Raspbien 64 bit, terry's latest build and it's slow.

If I had a spare Pi4 I'd use it.  I'd prefer a Pi5 with SSD on a bottom hat, but the 8G Pi5 is $100 more than I paid a couple of years ago ($265 CDN) so that's not feasible at the moment. I just can't see spending that much for a Pi5 at this time.

I've never tried a Pi Zero 2 W or any Pi Zero - mostly because the cost in Canada is NEVER close to your quoted $15. Usually much, much more. Sorry I can't help on that PI variant, but I suspect it would be slow based on my Pi 3B+ experiences. 

[Clem Cole]

some thoughts  below...

On Fri, Mar 27, 2026 at 2:07 PM Hugh Fisher <hvfi...@gmail.com> wrote:

Hello everyone - I'm new to the group. My PiDP-11 replica ships on Monday. Does anyone have recent experience running their replica, or even just running SIMH, on a Pi Zero 2 W?  Starting out, my use case is to run it headless and play with BSD 2.11 and ancient Unix over VNC (Wi-Fi). 

Functionally, it will work fine as it is more than adequate, but there are a number of dragons.  

I've got a couple of Pi 4s here that I'm using for other things, but I can pick up a 512MB Zero 2 W for $15 at Micro Center, so wanted to consider that as an option first.

Can you "borrow" the Pi4 to start to set up the SD card and core functionality?  Then move it to a different RPi 

I have both a PiDP-8 and a PiDP-11 [both from the first batch] running on a circa 2015 (original edition 32-bit) RPi 2, and both run fine.  Way more performance than a PDP 11/70 or a PDP-8/i

The Pi Zero 2 W has about the same processor performance and is 64-bit, but it has 1/2 memory and most importantly, a hardware ethernet.

WiFi is an issue when running emulated hosts (via SimH).  It's not SimH's fault; the problem is that few (if any) hosted OS's TCP/IP stack is aware of a wireless operation when those OSs are being run — and there isn't much SimH can do about it/fake out reality.  Think about it; in June 1983, IEEE 802.3/Ethernet was published, defining the core functions we all use.  It was not until 1997 that IEEE 802.1 [a.k.a. "WiFi"] came on the scene.  While .11 was based on .3, it is not the same and has characteristics that later IP implementations began to acknowledge.  Unfortunately for you, when ya user configure the networking stack in 2.11BSD [like TOPS-20 for the PiDP-10], it thinks it's talking to an actual DEC DEUNA or DELUA [or if emulating a QBUS DEQNA/DELQA].  The >> hosted OS really thinks it is on a direct connection wire.

Please be aware that when setting up the networking between the get SIMH configure and the hosted OS, there are many ways it can go wrong.  You can make it work, though there can be some annoying corner cases if you have a wireless connection for the network support in RPi hosting SIMH.  But it is not a recommended first instance.

My primary suggestion would be to take another RPi with a traditional RJ45 and plug it into a network hub before you touch the kit.  They are just concentrating on getting the core Linux functionality running, particularly if you are planning to use it sans a keyboard and display.  I might suggest starting with a display and keyboard, then turning on VNC and ensuring it works properly.  Or if you plan to really go without graphics on the RPi via its serial console, there are plenty of ways to have issues.

Once everything in RPi land is working well, install the PiDP-11 software. It will run fine without Oscar's hardware.  Bring up 2.11BSD [pro tip.  Start without the network for 2.11BSD; enable it after you're sure the basics are working.  If you want, and the RPi needs it, add a USB WiFI dongle.  But it would be a good time to ensure that Linux can see the Wi-Fi adapter, then try setting it up.   If you want to try to disconnect from the actual Ethernet and see how well 2.11.BSD handles being faked out [if you have issues, do a search on archives for this group, there are several ways this can break and what has been done about it].

So you now yopu have bits on an SD that match your intended use case; at this point, I would recommend making an image of the SD [so you know you can always get back to this point].

Now plug a USB-to-ethernet adapter into the RPi Zero platform and move the SD card you just set up to the other RPi.  At this point, functionality has not really changed.   If you have issues, debug them here.  You might want to try to figure out what is different besides the CPU switch.  It would be good to answer why the problem did not occur before.  Or can put the SD card back into the original RPi and see  if you see that same issue now. [Rince and repeat ...]

Assuming you now have everything working as you desire,  try removing the USB toEthernet.  Are there errors, what are they?

If you get here, we can now confirm you are ready to run the RPi Zero 22W with the configured SD card.  Go back to Oscar's instructions for when you match the RPi with his board and proceed from there.

[terri-...@glaver.org]

On Friday, March 27, 2026 at 3:14:48 PM UTC-4 sunnybo...@gmail.com wrote:

I just rebuilt my PiDP-11 system after the SD died after many years. I'm using a Pi 3B+, latest Raspbien 64 bit, terry's latest build and it's slow.

A Pi 3B+ with "throttle 1m" is roughly the same speed as a real 11/70.  I did a bunch of testing of the 3B+, 4B, and 5 back in 2024. I need to update the data with the results from a real 11/70 (and over the network to a real VAX 4000-705A for the network speed tests). See the attached text file.

 

If I had a spare Pi4 I'd use it.  I'd prefer a Pi5 with SSD on a bottom hat, but the 8G Pi5 is $100 more than I paid a couple of years ago ($265 CDN) so that's not feasible at the moment. I just can't see spending that much for a Pi5 at this time.

I've never tried a Pi Zero 2 W or any Pi Zero - mostly because the cost in Canada is NEVER close to your quoted $15. Usually much, much more. Sorry I can't help on that PI variant, but I suspect it would be slow based on my Pi 3B+ experiences. 

The various Pi implementations that have 40-pin GPIO do not all drive it the same way. Since the PiDP-11 emulator talks to the GPIO pins directly, it needs to "know" about a particular Pi model. I don't know if anything besides the 3B+, 4B, or 5 will work. I'd be glad to add support for other Pi models in my PiDP-11 development fork.

Unfortunately the AI crowd has cornered the market on DRAM, flash and disk storage so prices are likely to remain high until the AI bubble bursts. And the equipment that will be surplussed from those datacenters isn't really relevant to the Pi anyway - it's that manufacturers have diverted resources away from building stuff relevant to the Pi, so prices have gone up due to scarcity.  

It is also important to note that WiFi isn't really Ethernet - but the drivers at both ends make it look close enough to Ethernet that "normal" stuff works. Things like DECnet changing the card's MAC address, multicast support, etc. generally don't play nicely. There are things you can do with bridging and/or tunneling, but having an actual Ethernet connector on the Pi and using that is much simpler. In fact, wired Ethernet "just works" out of the box as long as you don't care about the emulated PDP-11 operating system being able to talk to the Pi that it is running on. Communicating with anything else on the LAN works fine.

[Whit Turner]

I built my PiDP-11/70 a few years ago with a Pi 3B+. More than adequate for most tasks, but running Lunar Lander with emulated Tektronix 4014 graphics would throw it into overheat/throttle mode.

I think the same goes for the PiDP-10 - if you want to do graphics, you'll likely need a Pi 5 (and mine runs the fan most of the time).

I don't have my PiDP-1 (yet), but given that many seem to be interested in graphics, I think the same situation will arise. For simple simulations and programming tasks, I agree that even a Pi Zero 2 would be fine.

My 2 cents.

Whit

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[terri-...@glaver.org]

On Friday, March 27, 2026 at 6:09:01 PM UTC-4 james.t...@gmail.com wrote:

I built my PiDP-11/70 a few years ago with a Pi 3B+. More than adequate for most tasks, but running Lunar Lander with emulated Tektronix 4014 graphics would throw it into overheat/throttle mode.

By default the Tek emulator causes the display server to become 100% CPU-bound. You can add "-fast" to the command line to avoid this. I need to look at the terminal emulators once I'm done with the main PiDP-11 code (most recently I was working on the new installer, but lately I've been busy with other stuff).

You might find my status.sh script from https://github.com/Terri-Kennedy/RPi-status useful as a way to measure your Pi's temperature, throttling, and fan speed (on Pi models like the 5 that support fan speed monitoring).

[Johnny Billquist]

That tek emulator is seriously broken, and is the source of all heat
problems (and a few others).

Johnny

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Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: b...@softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol

[Hugh Fisher]

Thanks for all the advice and feedback. To answer one question:

>Can you "borrow" the Pi4 to start to set up the SD card and core functionality?  Then move it to a different RPi 

Yes, I can, and that makes a lot of sense. I think I'll still pick up a Pi Zero 2 to play around with, with the expectation that it may not run very well.

I'm a newbie where the PDP-11 is concerned; my experience with this machine consists of reading PDFs of old manuals and watching Usagi Electric's videos. My goal with WiFi would be just to connect to the simulated PDP-11 in SIMH from a nearby laptop. Setting up TCP/IP and networking the simulated machine is going to take some learning on my part, but I'm sure I'll get there in time - fighting the "dragons" I encounter along the way. :-)

[Ken Hansen]

Just a datapoint - the processor in an RPi Zero 2W is the same as in the RPi 3B+, but with less RAM and fewer ports.

In my opinion, an RPi Zero 2W is fine for a PiDP-8, the RPi 4 is good for PiDP-11, and if you want to run everything on the PiDP-10, you want an RPi 5.

That said, I'm not sure how much RAM is needed on an RPi 4 or 5 for the PiDP-11 or PiDP-5 respectively, but an 8 Gig RPi 5 seems like overkill, expensive overkill for a simple, single-purpose PiDP-11 - RPi 4 are still available in many different RAM capacities.

An 8 gig RPi 5 is $120 in the states, a 16 gig Rapi 5 is $205, not sure why you are seeing $265 CDN for an 8 gig RPi 5 in Canada...

Ken

On Mar 27, 2026, at 13:07, Hugh Fisher <hvfi...@gmail.com> wrote:



Hello everyone - I'm new to the group. My PiDP-11 replica ships on Monday. Does anyone have recent experience running their replica, or even just running SIMH, on a Pi Zero 2 W?  Starting out, my use case is to run it headless and play with BSD 2.11 and ancient Unix over VNC (Wi-Fi). 

I've got a couple of Pi 4s here that I'm using for other things, but I can pick up a 512MB Zero 2 W for $15 at Micro Center, so wanted to consider that as an option first.

Thanks!

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[Whit Turner]

Prices are getting nutty again. 2 years ago I bought an 8GB Pi 5 from Digikey for $80. Now they want $172! And 6 months ago I bought a 4GB Pi 5 from Mouser for $60. Now they want $110.

There are plenty in stock, no surprise.

Whit

To view this discussion visit https://groups.google.com/d/msgid/pidp-11/F93B8F09-10DC-4B32-82C0-990132631BFE%40w5fc.org.

[sunnybo...@gmail.com]

Hopefully my images don't get this post deleted, but here are prices from amzn and digiky as of 1 minute ago... All prices $Canadian from the .ca versions of the sites

-r

[terri-...@glaver.org]

On Saturday, March 28, 2026 at 4:30:39 PM UTC-4 sunnybo...@gmail.com wrote:

Hopefully my images don't get this post deleted, but here are prices from amzn and digiky as of 1 minute ago... All prices $Canadian from the .ca versions of the sites

 

rpilocator - Find Raspberry Pi Computers in Stock shows the 1GB Pi 4B in stock at Pishop in Canada for CA $47.85: https://www.pishop.ca/product/raspberry-pi-4-model-b-1gb/

[John H. Reinhardt]

[Accidentally sent directly to Whit]

On 3/28/2026 1:35 PM, Whit Turner wrote:
> Prices are getting nutty again. 2 years ago I bought an 8GB Pi 5 from Digikey for $80. Now they want $172! And 6 months ago I bought a 4GB Pi 5 from Mouser for $60. Now they want $110.
>
> There are plenty in stock, no surprise.
>
> Whit
>

RaspberryPi has raised prices three times in the past few months. First in October on the Compute Modules
https://www.raspberrypi.com/news/5-10-price-increases-for-some-4gb-and-8gb-products/

Then in December on more general Raspberry Pi boards
https://www.raspberrypi.com/news/1gb-raspberry-pi-5-now-available-at-45-and-memory-driven-price-rises/

And most recently (at least acknowledged) in February
https://www.raspberrypi.com/news/more-memory-driven-price-rises/

I think there may have been a more recent increase not noted in the RaspberryPi News page.

The demand of AI for high-bandwidth memory (HBM) is causing memory producers to shift from consumer type chips to HBM resulting in a shortage which has driven prices up 300% or more.

https://counterpointresearch.com/en/insights/memory-price-tracker-january-2026

Experts say not to expect relief until sometime in 2027...

If you're looking for a Pi, check the authorized resellers first. They are by contract required to sell at the RaspberryPi suggested MSRP.  This means they can't charge a premium - at least they're not supposed to.  It also means they may be out of stock.  Other sellers, either through places like Amazon and Ebay are not authorized and can charge anything they want.


--
John H. Reinhardt