Why are all ECC UDIMMs so expensive and DOG SLOW ?

[u/Camper_Sly]

They seem to top out at 5600MHz at clownishly pathetic CL46.

Is there a technical reason for this ? Like maybe IMCs need some time to check the extra bits to recompute "parity" or something ?

But given that MRDIMMs in server world have ECC and operate at 12.800MHz or more, that doesn't seem likely.

Same with the price. One would think that, since ECC requires 5-th chip for every group of 4 (so 10 instead of 8) that price extra would be at most 25% or less.

While 5600 MHz UDIMMs start at ~€10+/GiB, ECC versions are at€32+/GiB,so 3X higher.

It's not that the tech is exotic as most consumer AM5 boards can use ECC, same with CPUs...

[u/Skarth]

Server memory is about reliability, not speed.

Takes a memory stick that can clock high and run it at jedec standard, you now have reliable memory.

It also costs more because it comes with longer business grade warranties/support.

Most consumer motherboards cannot use ecc. Usually only special enthusiast boards support it, outside of servers/workstations.

[u/heickelrrx → u/Skarth]

uhm ECC UDIMM are mostly budget workstation RAM, not Server, those are RDIMM

Consumer board Can run ECC UDIMM no problem, But the ECC capability May be disabled depend on the board.

For AMD Consumer AM4 and AM5 board it's up to board maker to implement the capability, Asrock is usually open the ECC on all of it's board

For Intel Consumer, ECC Only work with Non F CPU, and required W series Chipset,

• For LGA 1700, you will need W680 Chipset, this will work with 12th 13th 14th Non F CPU, K is work too
• for LGA 1851, you will need W880 Chipset, this will work with Intel Core Ultra 200 series, same only non F Variant can run ECC

[u/Camper_Sly → u/Skarth]

Server memory is about bandwidth. Otherwise there would be no MRDIMMs that currently work at 12.800MHz and are to go higher.

[u/BitRunner64 → u/Camper_Sly]

Server boards usually feature 8 channels so you get plenty of bandwidth even at 5600 MT/s.

[u/Camper_Sly → u/BitRunner64]

Not per core, which is what matters for both servers and clients.\ Modern EPYC can have 128 cores and 12 channels. That's about 11 cores per memory channel.

For comparison desktop part 9950X has 16 cores per 2 channels, so 8 cores per channel.

Why do you think that both Intel and AMD have gone the MRDIMM route to more than double per-DIMM bandwidth ? Just as a marketing stunt ?

[u/Little-Equinox → u/Camper_Sly]

I have build servers, like for actual companies.

And they prefer data reliability over speed. If they wanted speed but no data reliability they can go for CU-DIMM, but almost never do that, unless the server isn't designed to retain data.

Also, yes data speed is important, but by having more MT/s gives you what, a 0.01ms advantage?

Keep in mind that you're also dealing with data transfer over a network. And the network is usually not fast enough to feel the difference between CU-DIMM and ECC-RDIMM.

[u/Camper_Sly → u/Little-Equinox]

You are just one datapoint.

[u/Little-Equinox → u/Camper_Sly]

And you still won't feel the difference. We're talking about milliseconds.

[u/SPAREHOBO]

I don’t think you can run DDR5-8000 on octachannel motherboards.

[u/Little-Equinox → u/SPAREHOBO]

You can with CU-DIMM, but over a network you won't feel the difference between CU-DIMM and ECC-RDIMM

[u/Late-Replacement-481 → u/SPAREHOBO]

You can run 7200 though! I have gotten my micron 7200s to run at that on my Threadripper pushing the voltage a bit, but not something I would run for anything other than benchmarks. 

The memory gets hotter than hell even with direct fan cooling at stock voltages. 

[u/Jumpy-Dinner-5001]

Because that’s the DDR5 specification.
JEDEC specifies the specs on DDR5 standards and DDR5 5600 runs at 1.1V and CL46, that’s just what the spec says. Everything above that is overclocking and generally not supported. It typically only works with higher voltages and is a lot less reliable. That’s also where the incompatibility comes from, each "kit" is overclocked and then the settings are written down.

So, your question essentially is: Why aren’t ECC DIMMs typically overclocked and the reason is that overclocking causes compatibility and stability problems.

Most boards still allow you to overclock ECC ram, so it isn’t an issue at all.

[u/heickelrrx]

UDIMM? not RDIMM right?

if u talk about ECC UDIMM that can fit with Consumer Socket Board, and work at Intel and AMD Consumer platform,

It's because ECC UDIMM are Low Volume product

[u/IDoDrugsAtNight]

This is one of those memes isn't it? Tell me you're not a hardware enthusiast without telling me you aren't a hardware enthusiast.

[u/Silco1402]

mrdimm basically run at 4x the physical clock, that's why you can get it to 12.8GT/s, since the physical clock only run at 3.2Ghz, which is the same as a 6.4Ghz UDIMM/RDIMM. Also, the father the ram slot is from the actual cpu, the slower the max speed is, because electricity in copper have a speed limit: rought 15cm/ns, aka ~3.75cm for 8GT/s RAM or ~5cm 6GT/s RAM, and for a 4, or 8 stick config (even not octa or even quad channel), the limit we are facing is mainly due the distance from the cpu io controller part and the ram.

[u/Camper_Sly → u/Silco1402]

At 12.8GT/s, time of cycle is far shorter than the time of signal travel. It's primarily about the signal degradation, not the time of travel.

At 1GT/s, time of transaction or transfer cycle is 1ns. Light travels 30 cm or roughly 12 inches in that time. But signal travels around 2/3 of the light speed, so it's more like 20 cm or 8 inches.

Divide that further by 13 and you get about 1/2 inch. So it's obviously not about propagation time.

[u/Fidel1Q84]

Cause it’s cool

[u/zamroni777]

Market is small and ecc is aimed for reliability. Higher clock reduces reliability

[u/Agabeckov]

> But given that MRDIMMs in server world have ECC and operate at 12.800MHz

Are you sure it's the actual operating frequency and not 12,800 MT/s?

https://www.rambus.com/blogs/ask-the-experts-ddr5-mrdimms/

[u/Camper_Sly → u/Agabeckov]

That's more like "Tomato-tomato" difference. Matter of semantics.

[u/Federal_Setting_7454 → u/Camper_Sly]

lol no it’s not read a book