On 20-10-2020 11:21, Ahem A Rivet's Shot wrote:
> On Tue, 20 Oct 2020 07:50:30 +0100
> Andy Burns  wrote:
>
>> Martin Gregorie wrote:
>>
>>> I wonder how close in size that it to a mini-ITX motherboard and, if
>>> similar, do it's hold-downs match the mounting lugs in a mini-ITX case.
>>
>> CM4 is 55x40mm
>> miniITX is 170x170mm
>
>  Hmm rows of three mounted vertically, probably need about a 2cm
> pitch (height isn't specified) so a mini-ITX board with 24 compute modules
> could probably be built. The case would probably need to be mostly fan.

The connectors are on the bottom, though, not on the side like with the
SODIMM-like CM3, so you'd need some sort of adapter board which adds to
the height, plus room for up to 200 connections for each CM4. Well, I
haven't counted the actual number of signals... From the RPi blog: "two
high-density perpendicular connectors (one for power and low-speed
interfaces, and one for high-speed interfaces)" and from the datasheet:
"The electrical interface of the CM4 is via two 100-pin high density
connectors" and "The Module is 4.7 mm deep, but when connected the
height will be 5.078 or 6.578 mm depending on the stacking height
chosen." It also lists the complete pin-out:
https://datasheets.raspberrypi.org/cm4/cm4-datasheet.pdf

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