AMD patch confirms Zen 4 Epyc will support 12-channel DDR5 RAM

Daniel Sims

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In brief: A new Linux driver for AMD’s Epyc server CPUs has added support for the company’s upcoming Zen 4 generation of processors. The patch notes mention DDR5 RAM along with some other details regarding memory.

The latest Linux Error Detection And Correction driver for Epyc processors adds support for AMD’s 19h, 10h-1Fh, and A0h-AFh models, as well as Registered DDR5 (RDDR) and Load-Reduced DDR5 (LRDDR) memory. AMD’s current Epyc CPUs only support DDR4 RAM, and we already know Zen 4 will work with DDR5.

RDDR and LRDDR are types of memory used for servers. Compared to typical DDR, the former offers them higher bandwidth and scalability, while the latter supports higher-density memory.

While the current Epycs are limited to eight memory controllers per socket, the patch confirms Zen 4 will have 12. It’s unclear how much of this information could apply to Zen 4 desktop CPUs.

Over the summer, AMD confirmed Zen 4 was on track to launch next year. Made on TSMC’s 5nm node, the processors are expected to support AM5 sockets and PCIe 5.0. In November, AMD revealed the “Genoa” and “Bergamo” data center Zen 4 CPUs, which should launch in 2022 and 2023, respectively. Genoa will come with 96 cores while Bergamo, designed for cloud data centers, will have 128.

The desktop Zen 4s are expected to max out at 16 cores.

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HardReset

Posts: 1,625   +1,275
While the current Epycs are limited to eight memory controllers per socket, the patch confirms Zen 4 will have 12. It’s unclear how much of this information could apply to Zen 4 desktop CPUs.
Since DDR5 is essentially dual channel DDR4 with one DIMM, not hard to guess desktops will support at most "dual channel DDR5". Threadripper is another question, probably "six channel DDR5" there.
 

yRaz

Posts: 4,334   +4,968
Since DDR5 is essentially dual channel DDR4 with one DIMM, not hard to guess desktops will support at most "dual channel DDR5". Threadripper is another question, probably "six channel DDR5" there.
are you talking about clock speed or do DDR5 dimms have essentially 2 internal channels?

I also don't understand why they limit desktops to 2 channels. The professional market isn't going to stop buying highend parts just because a 16 core part now supports 4 channels. I know gamers don't exactly NEED 4channels but there is no reason not to give it to them. Pixar isn't going to start buying desktop ryzen parts just because they went from 2 channels to 4.

For the professional market cost really isn't an issue, getting maximum performance is.
 

HardReset

Posts: 1,625   +1,275
are you talking about clock speed or do DDR5 dimms have essentially 2 internal channels?

I also don't understand why they limit desktops to 2 channels. The professional market isn't going to stop buying highend parts just because a 16 core part now supports 4 channels. I know gamers don't exactly NEED 4channels but there is no reason not to give it to them. Pixar isn't going to start buying desktop ryzen parts just because they went from 2 channels to 4.

For the professional market cost really isn't an issue, getting maximum performance is.
Internal memory channels. That makes talking about memory channels bit harder. We probably need new term for that.

Quad channel memory makes motherboards much more expensive. Offering quad channel for desktops would create two categories for motherboards: one support dual channel and another support quad channel. Cheap motherboard with quad channel is pretty much no go. Also there would be need for two different sockets, again cheap motherboards don't want too many pins on socket/LGA. Because AMD already have different Threadripper line for quad channel, why they should make another one for desktops?
 

Puiu

Posts: 5,463   +4,394
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are you talking about clock speed or do DDR5 dimms have essentially 2 internal channels?

I also don't understand why they limit desktops to 2 channels. The professional market isn't going to stop buying highend parts just because a 16 core part now supports 4 channels. I know gamers don't exactly NEED 4channels but there is no reason not to give it to them. Pixar isn't going to start buying desktop ryzen parts just because they went from 2 channels to 4.

For the professional market cost really isn't an issue, getting maximum performance is.

More memory channels add a lot of complexity and cost to both the CPUs and motherboards. it makes sense to have them added to workstation class hardware although high end desktop CPUs could definitely use the extra bandwidth.
 

Avro Arrow

Posts: 2,204   +2,591
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What happened to their 256-core, 512-thread monster? I guess it became another casualty of the silicon shortage. When the competition already can't match what you have, it's better to spread things out a bit so that nobody gets left out in the cold. That means you can take care of more customers and create more relationships which helps you in the long-term.

I hope that AMD keeps using DDR4 for the home desktop platform because DDR5 isn't appreciably faster than DDR4 at this time but you can be damn sure that it'll be more expensive regardless.
 
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HardReset

Posts: 1,625   +1,275
What happened to their 256-core, 512-thread monster? I guess it became another casualty of the silicon shortage. When the competition already can't match what you have, it's better to spread things out a bit so that nobody gets left out in the cold. That means you can take care of more customers and create more relationships which helps you in the long-term.
Rumored for Zen5, not coming until about 2024 earliest.
 

yRaz

Posts: 4,334   +4,968
More memory channels add a lot of complexity and cost to both the CPUs and motherboards. it makes sense to have them added to workstation class hardware although high end desktop CPUs could definitely use the extra bandwidth.
I mean I guess it's easier to just add cache to a CPU, but we're getting to the point with all these cores that we kinda need more memory channels. 8 cores are becoming the standard and we're probably only two generations away from 16 cores becoming standard. It's nice to have multiple cores but they need bandwidth.

I think DDR5 will slow down the idea of going from 2 channels to 4, but I I have a feeling that day is coming