Using an m.2 hat with the PiDP-10 + short intro

[John Johnson]

Hello!

New to the group, and glad to find like minded people. Had a pdp-11/23, (w/ terminal, dual 8” floppies) a long time ago that was used as a sort of smart terminal attached to an HP system. Always been interested in DEC stuff. I also have an Altairduino, and a Netronics ELF-II I put together in 1982. But basically everything I wanted as a teen/young adult I still want. lol

.

I  haven’t bought a pidp-10 kit yet, but got my rpi setup yesterday.

When assembled, the stacking connector for the gpio pins doesn’t extend above the m.2 hat.

I think I’ve seen mention of the hat being used in this group. How does that work?

Is it a matter of balancing seating on the Pi with pins protruding above?

Or are there triple-height stacking connectors?

Or…?

[Kind of torn between the PiDP-10 and PiDP-11.)

Thanks for any info!

John

[Steven A. Falco]

There should be a lot of information in the list archives, but I can say that my setup uses a Pimoroni NVMe board that mounts on the back side of a Pi 5. That way, the cooling fan for the Pi CPU is unaffected and I don't have to worry about the connector heights.

I attached one of my emails from last year - it has more details and a photo. After using this for a year I wouldn't change a thing. It runs 24/7 very reliably.

Steve

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[terry-...@glaver.org]

On Sunday, June 29, 2025 at 8:31:06 AM UTC-4 jjte...@gmail.com wrote:

I think I’ve seen mention of the hat being used in this group. How does that work?

I have a bunch of the Pimoroni bottom-mount boards coming for use on the PiDPs.

I originally felt that the transfer rate of a SDXC card was so much faster than the maximum speed of the Unibus (3Mbyte/sec)  or Massbus that I didn't need something faster. The problem is that the transfer rate is not constant - the more data you write, the slower the SDXC card gets. This leads to extra lag in the emulation (the emulated OS is doing a write and waiting for completion).

I run a bunch of Pi 5s (not in PiDPs) emulating part of the DEC section of the SPC* Academic Computer Center - a pair of VAX 8650s and a pair of PDP-11/70s, each on its own Pi 5. I decided to try the official Pi M.2 HAT+ and a $25 Kioxia BG6 256GB NVMe drive on one of the Pi 5's (in this case, in the emulated VMS environment - backing up and verifying a mostly-full 2GB RA92 to another RA92 on the emulated system, as well as a 32GB  'dd' in the Pi OS bash shell) and the difference was amazing. First, the SDXC:

SPCVXA::$ @benchmark
  26-JUN-2025 20:08:31
%BACKUP-I-STARTVERIFY, starting verification pass
  27-JUN-2025 04:23:41
8 hours 15 minutes, mostly in write phase.

root@spcvxa-host:/home/pi# dd if=/dev/zero of=tmp.tmp bs=1M count=32000
32000+0 records in
32000+0 records out
33554432000 bytes (34 GB, 31 GiB) copied, 1174.98 s, 28.6 MB/s

Now, the NVMe with the exact same files (copied from the SDXC card):

SPCVXA::$ @benchmark
  27-JUN-2025 14:32:42
%BACKUP-I-STARTVERIFY, starting verification pass
  27-JUN-2025 17:15:43
2 hours 43 minutes, mostly in write phase.

root@spcvxa-host:/home/pi# dd if=/dev/zero of=tmp.tmp bs=1M count=32000
32000+0 records in
32000+0 records out
33554432000 bytes (34 GB, 31 GiB) copied, 38.5643 s, 870 MB/s

Needless to say, the other 3 systems got HATS and NVMe cards as well.

* Refer to https://www.glaver.org/blog/?p=926 for  more info

[Steven A. Falco]

I suspect you will also see an improvement in lifespan with the M.2 cards, at least if they are of high quality.

Since the M.2 cards are intended to replace the hard drives in laptops and desktops and are therefore a bit difficult to replace, they have to have a good lifespan. In contrast, uSD cards are often used in cameras and can be treated as more ... disposable. :-)

Steve

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[John Johnson]

Ah! Okay.

I thought the gpio connector was used for something, but it runs fine disconnected. 

I’ll get some short standoffs and mount mine on the back too. 

Thanks Steve!

[John Johnson]

Not sure why my reply with pics was deleted, but thanks!
I can remount mine on the back using shorter standoffs.

On Sunday, June 29, 2025 at 10:38:30 AM UTC-4 steve...@gmail.com wrote:

[John Johnson]

Thanks for the replies!
(My replies yesterday were being deleted ¯\_(ツ)_/¯)
Anyway, I ordered some standoffs, and will remount the m.2 hat to the bottom of the pi, just flip it around.
I didn't realize the gpio connections to it weren't used, but it runs fine detached.
Thanks again!

[Chuck McManis]

I also note that the m.2 drive can get warm itself. I've not had any issues with overheating but it is a thing,

--Chuck

[Andrew Barron]

I am using a Pineberry 'Pinedrive 256GB' M.2 hat for my Pi5. Pineberry has two models. I picked the one that mounts on the back because I needed the 40 pin header to be free of obstructions. 

The only change I had to make to the PiDP-10 was to mount the nylon mounts upside down.