What is the point of using CM4 instead of Pi4?

[raspberry_user]

Hi, somebody said that the CM4 is faster and smaller than the Pi4. However, the CPU on both seem to be the same and in order to use GPIO/I2C, we need to buy an I/O board that ends up having a larger unit than the Pi4. So what is the point of using the CM4 besides the additional support for eMMC and PCI SSD? Is the memory speed and system bus speed the same on both products? It looks like if I need GPIO/I2C, better to just stay with the Pi4?

[W. H. Heydt]

Where did you read that the CM4 is faster? As you note, it's the same SoC as the PI4B, so the speed is the same.

CMs are, generally speaking, for industrial and embedded applications. While you can just plunk a CM4 on the IO board--and you're right that it's bigger, but it also has features that a Pi4B does not--the usual course is for a company to design and implement a carrier board with only the features they actually want in their product, and is--therefore--likely to be rather smaller.

For the overall user community, CMs, and in particular, the CM4 are a non-issue.

The end user interest in some quarters is driven, I think, by some of those extra features on the IO board: RTC, fan header, optional external antenna, ability to take 12v (or more) input power, and--especially--the PCIe connector. If those are things you want, or think you need, then the CM4/IO board might be pretty exciting. If a Pi4B has basically everything you're looking for, then ones reaction to the CM4 is likely to be, that's nice, let me know when something interesting comes along.

And for those thinking of the CM4 as a super-charged Pi0/Pi0W, you'll really need a carrier to go with. I would imagine someone will manage to make a carrier board that isn't much bigger (if any at all) than the CM4 itself. But it's probably going to take a bit.

[aBUGSworstnightmare]

CM4 is intended for industrial use, with users developing their own full-custom-to-their-needs baseboard. The CM4IO is just intended for development purpose, although it will be a product in it's own.

[ejolson]

Hi, somebody said that the CM4 is faster and smaller than the Pi4. However, the CPU on both seem to be the same and in order to use GPIO/I2C, we need to buy an I/O board that ends up having a larger unit than the Pi4. So what is the point of using the CM4 besides the additional support for eMMC and PCI SSD? Is the memory speed and system bus speed the same on both products? It looks like if I need GPIO/I2C, better to just stay with the Pi4?

That's right. The CM4 is for industrial users putting them inside of stuff where they will be directly connected to a custom-built circuit board with lots of special-purpose features. For the hobbyist-maker community the Pi 4B is much easier to work with.

The nice thing is that if the software for your one-off build turns out to work well and generate interest from others, you could hire an engineer to convert the hardware part of the project to an CM4 based system that is easy to manufacture at scale.

In my opinion, it's seriously important to consider the alternative of open-source fame before trying to make a closed-source fortune.

[raspberry_user]

I read that the CM4 is faster from one of the reviewers. Don't remember who that is. Am I correct that if I don't use GPIO ports, then the CM4 is good as it is smaller than the Pi4 and it has eMMC builtin without the need to have an I/O board? I know eMMC is faster than SD card. How is eMMC compared with SSD and USB 3.1 memory stick?

[trejan]

I read that the CM4 is faster from one of the reviewers.

Same speed. It has the same SoC as the Pi 4 and runs at the same 1.5GHz.

without the need to have an I/O board?

You need some kind of I/O board as there is no way to connect to the CM4 without it. It may be a custom one designed for your specific device or a generic one like the official Compute Module I/O board.

If the Pi 4 does everything you need then you don't need to use a CM4.

[fruitoftheloom]

I read that the CM4 is faster from one of the reviewers. Don't remember who that is. Am I correct that if I don't use GPIO ports, then the CM4 is good as it is smaller than the Pi4 and it has eMMC builtin without the need to have an I/O board? I know eMMC is faster than SD card. How is eMMC compared with SSD and USB 3.1 memory stick?

Please stop reading unsubstantiated rubbish, just read the Official Blog.

You need an I/O base board, it will not function without

https://m.youtube.com/watch?feature=you ... iHgmNBOzkc

[jamesh]

In my opinion, it's seriously important to consider the alternative of open-source fame before trying to make a closed-source fortune.

Fame is well know for paying the mortgage. Unlike money.

Or is it the other way round?

[ejolson]

I read that the CM4 is faster from one of the reviewers. Don't remember who that is. Am I correct that if I don't use GPIO ports, then the CM4 is good as it is smaller than the Pi4 and it has eMMC builtin without the need to have an I/O board? I know eMMC is faster than SD card. How is eMMC compared with SSD and USB 3.1 memory stick?

I suspect since the CM4 is smaller it will more likely need a heatsink. Also, like you said, it is not smaller once it is attached to the carrier board.

One question to ask when trying to understand the CM4 is what custom circuitry do you want on the carrier board that is not included in the 4B already. If the answer is none, then the CM4 is not for you.

[davidcoton]

In my opinion, it's seriously important to consider the alternative of open-source fame before trying to make a closed-source fortune.

Fame is well know for paying the mortgage. Unlike money.

Or is it the other way round?

That's why you (and I) are not rich. Or famous.

[ejolson]

In my opinion, it's seriously important to consider the alternative of open-source fame before trying to make a closed-source fortune.

Fame is well know for paying the mortgage. Unlike money.

Or is it the other way round?

My understanding is that working for someone else is usually the way to pay the mortgage. In most cases that leads to neither fame nor fortune, though it's possible, but only if that someone else has really good ideas.

[jamesh]

A tiny amount of airflow over the CM4 will cool it sufficiently not to need a heatsink. If the device is not loaded particularly heavily you won't need either in most circumstances.

[lurk101]

My understanding is that working for someone else is usually the way to pay the mortgage. In most cases that leads to neither fame nor fortune, though it's possible, but only if that someone else has really good ideas.

I can count on the fingers of one hand those who have achieved fame through open source. Mostly it's abandoned projects, developer burnout, or corporate capture.

[W. H. Heydt]

I read that the CM4 is faster from one of the reviewers. Don't remember who that is. Am I correct that if I don't use GPIO ports, then the CM4 is good as it is smaller than the Pi4 and it has eMMC builtin without the need to have an I/O board? I know eMMC is faster than SD card. How is eMMC compared with SSD and USB 3.1 memory stick?

The eMMC on any CM, other than the original CM, is optional (see the "CM* Lite versions). However, you still need a carrier board, even if the carrier has nothing but a power connector on it (probably not practical to connect the required 5v supply directly to high density connectors on the CM4).

What I expect to see in relatively short order will be a minimal carrier that gives the standard GPIO block, a single USB 2 data connector, some form of HDMI connector, maybe a CSI connector, perhaps some sort of PCIe connector, and a power connector. In other words, something that looks like a "super-charged", slightly larger and thicker, much more power hungry Pi0/Pi0W.

[lurk101]

A tiny amount of airflow over the CM4 will cool it sufficiently not to need a heatsink. If the device is not loaded particularly heavily you won't need either in most circumstances.

Does it incorporate a large heat spreading copper plane like the Pi4?

[ejolson]

My understanding is that working for someone else is usually the way to pay the mortgage. In most cases that leads to neither fame nor fortune, though it's possible, but only if that someone else has really good ideas.

I can count on the fingers of one hand those who have achieved fame through open source. Mostly its abandoned projects, developer burnout, or corporate takeover.

Admittedly those who achieve either fame or fortune are rare. Comparing how many in each category may be better left to a different thread.

One difference, however, is that going out of business instead of making a fortune with closed source code is a complete loss, whereas, a failed open source project can be appreciated and even built upon by anyone else at a later time.

[davidcoton]

What I expect to see in relatively short order will be a minimal carrier that gives the standard GPIO block, a single USB 2 data connector, some form of HDMI connector, maybe a CSI connector, perhaps some sort of PCIe connector, and a power connector. In other words, something that looks like a "super-charged", slightly larger and thicker, much more power hungry Pi0/Pi0W.

And a DSI connector, pretty please. (To my mind the most potentially useful omission from the Pi0.)

[davidcoton]

One difference, however, is that going out of business instead of making a fortune with closed source code is a complete loss, whereas, a failed open source project can be appreciated and even built upon by anyone else at a later time.

Well, you can always open the source when the business fails.

[W. H. Heydt]

What I expect to see in relatively short order will be a minimal carrier that gives the standard GPIO block, a single USB 2 data connector, some form of HDMI connector, maybe a CSI connector, perhaps some sort of PCIe connector, and a power connector. In other words, something that looks like a "super-charged", slightly larger and thicker, much more power hungry Pi0/Pi0W.

And a DSI connector, pretty please. (To my mind the most potentially useful omission from the Pi0.)

I considered adding that in.... Add that to a "Pi0-like" board and then combine the result with an RPF 7" display, using it with the RPF keyboard (because of the built in USB hub), and it'd be a fairly slick system.

[raspberry_user]

Anybody knows why the I/O Board came with USB2 rather than USB3? To use USB3, one has to insert a big USB3 adapter to that PCI slot that could be better used for something else.

Anybody knows the actual weight of the I/O Board? It looks very big.

[trejan]

Anybody knows why the I/O Board came with USB2 rather than USB3? To use USB3, one has to insert a big USB3 adapter to that PCI slot that could be better used for something else.

The USB 3 controller on a Pi 4 is attached via PCIe. If you had that on the CMIO then you wouldn't have a PCIe slot...

[jdb]

I read that the CM4 is faster from one of the reviewers. Don't remember who that is.

Fortunately, you don't have to remember.

Your browser history saves that information for you.

What website lead you to form the opinion that "CM4 is faster"?

[trejan]

What website lead you to form the opinion that "CM4 is faster"?

There are lots of poorly written articles out there about the CM4 because they all seem to be copying from each other. They're trying to say faster than previous CMs but the way they've written it sounds like it is faster than a Pi 4.

Whoever did the Techradar article messed up so badly that they've used a photo of a Rock Pi.

The Compute Module 4 is built using the same 64-bit quad-core processor as the one used for the standard model of the Raspberry Pi 4, but it also boasts faster CPU cores, more interfacing capabilities, a wireless connectivity option and much more to improve its suitability for deeply-embedded applications.

[W. H. Heydt]

Anybody knows why the I/O Board came with USB2 rather than USB3? To use USB3, one has to insert a big USB3 adapter to that PCI slot that could be better used for something else.

The simplest answer is: Because the BCM2711 (the SoC used on the Pi4B and the CM4) doesn't *have* a USB 3 interface. It does have a USB 2 interface. The reason a Pi4B has USB 3 ports is because the single PCIe lane that is part of the SoC is connected to a PCIe-to-USB hub, and it supports USB 3.

So...for development purposes, the best use is to directly expose the PCIe lane and let the carrier board developer decide what to do with it...which *might* be USB 3...or it might not.

Anybody knows the actual weight of the I/O Board? It looks very big.

Not sure the weight is relevant to anything. It is significantly larger that a B-series Pi, but there are some good reasons for that. I has a lot more on it than there is on a B-series Pi. It has the usual stuff...40-pin GPIO block, 4-pin PoE header, a pair of USB 2 ports, a micro-SD slot. It also has an empty space to attach the CM4. In addition, there is a power distribution section that can handle up to 26v (which has to be limited to 12v if you're going to use the PCIe connector). It has that PCIe connector. It has a USB micro-B connector for programming the eMMC flash on the CM4. It has (I'm told) a fan header. It has an RTC and a battery holder. It has a pin header for 2 more USB 2 ports.

The features of the IO board aren't crammed together. They're spread out where you can get at them without having attachments interfering with each other. The object is to give people easy access to as much as possible, rather than to make a board that is as compact as possible. Third-party developers will likely strive for significantly more compact--and likely far more expensive--designs.

[Gavinmc42]

Gumstick must have had early prototypes/data
They already have some simple IO boards.
We will probably see more appear sooner or latter.

With the standard Pi's you are limited to that footprints.
Embedding CM4s will be easier as it is smaller.
Easier for the industrial guys, who seem to take 50% of Pi sales if I heard Eben correctly.
32 versions now makes Raspberry a serious leader in this area?

They may have annoyed existing CM3 users with the changes.
I suspect the CM4 market is going to be bigger than all previous CM's.

Just guessing but looking at that BCM2711 SoC on the micro PCB, the CM4 PCB might be able to take the older SoC's too?