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Comment by doikor | Hacker News Reader

With DDR5 it is very unlikely that you are going to add more memory modules on consumer boards. This is because if you add more then 2 you half the speed on both AMD and Intel platforms (and you don't get full speed with just 1 stick). Also if the new module is not exactly the same as the previous ones you can very easily run into stability issues.

This is why on consumer land you are pretty much always buying your memory as a kit (of 2 modules with DDR5). And if you want more you buy a bigger kit and sell your old ones or throw them in the trash.

On server side the memory controller on the CPU is much more beefy and the motherboard better built to allow for more memory sticks to run at full speeds. But even then you usually have to go and find memory that the OEM qualified/teste for you.

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> This is because if you add more then 2 you half the speed on both AMD and Intel platforms (and you don't get full speed with just 1 stick).

Modules have been added in pairs since forever due to motherboards being able to use dual channel. Except on the cheapest cheapest options (not all laptops).

That doesn't mean you can't add more than one pair.

Did that change with DDR5?

Also note that this CAMM module is already dual channel. You don't need pairs any more.

Yes, four slot DDR5 is going to be much slower than two slot DDR5 due to signal integrity difficulties. Look at a DDR5 motherboard’s qualified memory configurations and compare the x2 setups to x4 and you will see the huge difference in clock rates.

If that's the case, would it be possible to deactivate those sticks for extra speed if memory usage is currently low?

The calibration to get just 2 sticks to be stable is around 20-50 seconds already, during which the memory controller is testing different sequencing and even clocks for individual lanes to minimize interference. So unless you want to stop the entire CPU if you need that memory, no.

You're running a signal at 2.4+ GHz (commonly 3 GHz for DDR5-6000) over 288 pins over several centimeters simultaneously, it's not pretty.

No, the signal integrity loss is caused by the physical presence of the additional modules.

What's "much slower"? 10%? 30%? 60%? Are the speeds that don't work in an x4 configuration even within spec, or "overclocked"?

Is that why everyone is complaining about ddr5 prices? Atm I'm fine with my ddr4 box and will probably still be for the next few years.

Tbh the last time I've seen a noticeable difference from memory speed was when I overclocked my ram (and system bus!) from 66 to 100 Mhz. Back in the pentium 1 / amd k5 era, i believe.

I do have a feeling what you're describing only means 5 more fps in some benchmarks...

And last, a friendly reminder. If your working set doesn't fit in ram you're screwed no matter what your ram speed is :)

As doikor said, it’ll halve your RAM speed. That’s not a rule, but it’s typical.

So... if you want a reasonable amount of ram for real work (64 G+) you're better off with ddr4?

You just buy large modules. There are 64 and 128gb modules (mainly meant for servers)

For example 64gb from Samsung for 350€ https://www.dateks.lv/en/cenas/atmina-ram/1028642-samsung-64...

I think they go up to 512gb per single module these days. The really big ones are really hard to buy for us mere mortals but you can get them through various data center/enterprise hardware vendors.

> Also if the new module is not exactly the same as the previous ones you can very easily run into stability issues.

Even with the same module, syncing up 4 modules to rated speed is going to be a challenge to boot, let alone have it be stable. If you want density, a platform that supports RDIMMs is the way to go with DDR5.

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