[NetMageSCW]

>The sad part is that DDR5 is the thing that doesn't need to be soldered, unlike GDDR. But then Apple solders it anyway.

Apple needs to solder it because they are attaching it directly to the SOC to minimize lead length and that is part of how they are able to get that bandwidth.

[AnthonyMouse]

Systems with socketed RAM have had on-die memory controllers for more than two decades. CAMM2 supports the same speeds as Apple is using in the M5.

[foldr]

CAMM2 most likely wouldn't work for the Max and Ultra chips:

https://news.ycombinator.com/item?id=43266848

https://news.ycombinator.com/item?id=43267075

[AnthonyMouse]

The logic of those posts is questionable.

The premise of the connector is that it attaches to the board in a similar way as soldering the chips (the LPCAMM connection interface is directly on the back of the chips) but uses compression instead of solder to make the electrical connection, so the traces are basically the same length but the modules can be replaced without soldering. There is no reason you couldn't use two modules to get a 256-bit memory bus. It sounds like AMD designed Strix Halo to assume soldered memory and then when Framework asked if it could use CAMM2 with no modifications to the chip, the answer was yes but not at the full speed of the CAMM2 spec.

CAMM2 supports LPDDR5X-9600, which is the same speed Apple uses in the newest machines:

https://www.micron.com/content/dam/micron/global/public/docu...

The Max chips have a 512-bit memory bus. That's the one where the comment you linked suggests putting one module on each side of the chip as being fine, and there is no M4 Ultra or M5 Ultra so they could be using LPCAMM2 for their entire current lineup. The M3 Ultra had a 1024-bit memory bus, which is a little nuts, but it's also a desktop-only chip and then you don't have to be fighting with the trace lengths for LPDDR5 because you could just use ordinary DDR5 RDIMMs.

[foldr]

> but uses compression instead of solder to make the electrical connection

This is still going to have higher parasitic resistance and capacitance than a soldered connection. That's why it's not just a drop-in replacement for soldered RAM. You'd either have to use more power or run the RAM slower.

> one module on each side of the chip as being fine.

It's fine if you've got space to spare. It's not very practical for a laptop form factor.

>but it's also a desktop-only chip and then you don't have to be fighting with the trace lengths for LPDDR5 because you could just use ordinary DDR5 DIMMs.

Given how few desktops Apple sells compared to laptops, I seriously doubt that they'd want to use a completely different memory configuration just for their desktop systems.

[AnthonyMouse]

> This is still going to have higher parasitic resistance and capacitance than a soldered connection. That's why it's not just a drop-in replacement for soldered RAM. You'd either have to use more power or run the RAM slower.

This isn't accurate. A compression interface can have the same resistance as a soldered connection.

There is a small infelicity with DDR5 because the DDR5 spec was finalized before the CAMM2 spec and the routing on the chips isn't optimal for it, so for DDR5 CAMM2 requires slightly tighter tolerances to hit 9600 MT/s, which is presumably the trouble they ran into with Strix Halo, but even then it can do it if you design for it from the beginning, and they've fixed it for DDR6.

> It's fine if you've got space to spare. It's not very practical for a laptop form factor.

The modules take up approximately the same amount of space on the board as the chips themselves. It's just a different way of attaching them to it.

> Given how few desktops Apple sells compared to laptops, I seriously doubt that they'd want to use a completely different memory configuration just for their desktop systems.

DDR5 and LPDDR5 are nearly identical, the primary difference is that LPDDR5 has tighter tolerances to allow it to run at the same speeds at a lower voltage/power consumption. When you already have the design that meets the tighter tolerances, relaxing them in the system where you're not worried about 2 watts of battery consumption is making your life easier instead of harder.

[foldr]

>This isn't accurate. A compression interface can have the same resistance as a soldered connection.

All the information I can find suggests that CAMM2 will have higher parasitic resistance and capacitance than a soldered connection. Do you have a source for this claim?

The issue isn't just reaching a certain speed, but doing it at the same power consumption.

>The modules take up approximately the same amount of space on the board as the chips themselves.

They do take up more space, as anyone can easily check. Modern laptop motherboards can be very small, so this is significant.

>DDR5 and LPDDR5 are nearly identical [...]

What I mean is that Apple isn't going to want to invest any resources in adding the option of external RAM just for the relatively tiny desktop market. It's not that it's technically difficult; it just doesn't make sense from a logistical point of view.