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Question about large DIMMs

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zachj

Chainsaw Senior
Joined
Aug 19, 2002
Location
Redmond, Washington
DISCLAIMER: I am not asking if my particular motherboard support 32GB DIMMs; I'm asking a general question about large-capacity DIMMs.

Does anyone know what is technically required for a motherboard to support 32GB/64GB RDIMMs or LRDIMMs? Obviously the CPU (with integrated memory controller) and presumably also the chipset, but what else? Is there something at the BIOS level that is required to support these? Is there some other physical design/component required (like extra copper in the memory traces to handle higher memory loading)?

I ask because there are a ton of motherboards (OEM and otherwise) that list support for 16GB RDIMMs but make exactly zero mention of support for higher capacity DIMMs. Importantly, no manufacturer explicitly states that 32GB DIMMs won't work; they simply list what does work, and from this it isn't clear whether the implication is that 32GB DIMMs physically won't work or merely that the manufacturer hasn't bothered to perform validation testing...

While I'm generally of a mind to just try it to see if it works, 32GB DIMMs aren't cheap and I'm not keen on paying a 15% restocking fee + return shipping on such an expensive component.

Thanks
Z
 
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trents

Senior Member
Joined
Dec 27, 2008
Be careful in concluding that an amount of RAM above the stated max capacity is actually being used even when that amount is reported by Windows.
 
OP
zachj

zachj

Chainsaw Senior
Joined
Aug 19, 2002
Location
Redmond, Washington
I have previously read similar guidance but I don't see much in the way of concrete facts around when and why issues will arise. I've certainly seen plenty of posts about how Windows won't display the right amount (ex: 32-bit Windows won't allow more than 4GB, iGPU gobbles up extra memory, etc.) but posts about issues when using too-large DIMMS are much rarer.

Let me ask it this way:
  1. Must there be BIOS-level support for LRDIMMs? Or are they supported as long as the chipset and processor support them?
  2. If there are physical requirements for large DIMM support beyond chipset/CPU, what are they?

My sense is that HP could have added 32GB LRDIMM/RDIMM support for the Z420/Z620 if they wanted to, but elected not to solely for the sake of product segmentation. The question is whether this was merely validation--in which case it would probably work today without being officially supported--or if there was actual modification required to BIOS/hardware to make it work--in which case clearly it won't work.

Thanks
Z
 
OP
zachj

zachj

Chainsaw Senior
Joined
Aug 19, 2002
Location
Redmond, Washington
Question about 32GB/64GB DIMMs

DISCLAIMER: I am not asking what's supported; I'm asking what is required to make it physically work (whether or not officially supported).

Does anyone know if there's a physical/BIOS requirement beyond CPU/chipset in order for a motherboard to accept large capacity RDIMMs/LRDIMMs (i.e. 32GB and 64GB DIMMs)? I've posted a related question elsewhere on the forum, but it occurs to me that the memory sub-forum might be the better place to ask...

Specifically, if I've got a motherboard with a C602 chipset and a Xeon E5-2660v2 CPU, is that all I need to guarantee functionality of 32GB RDIMMs/LRDIMMs or must the BIOS/firmware also specifically implement code for the large capacity DIMMs? Are there other more arcane physical components required to enable large capacity DIMMs (ex: more copper in the memory traces to reliably handle the higher loading)?

While I'm generally a subscriber to the "why don't you try it and see if it works" school of hard knocks, I'm not remotely interested in spending upwards of $250 on a stick of RAM I might not be able to return.

Thanks
Z
 
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Johan45

Benching Team Leader Super Moderator
Joined
Dec 19, 2012
You might want to check the details on your motherboard at their site. QVL list etc..
You'll need to do some work I think. I went to the crucial site following a google of 32 gb dimms found a 4x32 set low speed microns punched in your workstation details and came back not compatible.
 
OP
zachj

zachj

Chainsaw Senior
Joined
Aug 19, 2002
Location
Redmond, Washington
I know for a fact that HP lists the Z420/Z620 as not supporting 32GB DIMMS (neither LRDIMMs nor RDIMMs). But just because they're not supported doesn't mean they don't work...

Hence my question: what's actually required for 32GB DIMMs to function (whether officially supported or not)?

Thanks
Zach
 

trents

Senior Member
Joined
Dec 27, 2008
It is a fact that 32-bit Windows cannot USE more than 4gb of RAM. That is a limitation of the 32-bit code algorithm of the OS.
 
OP
zachj

zachj

Chainsaw Senior
Joined
Aug 19, 2002
Location
Redmond, Washington
Of that I am most certainly aware...

Again, my question is about using DIMMs that are higher-capacity than what the motherboard manufacturer officially supports. Where a motherboard manufacturer states support for 16GB RDIMMs, what happens if I use 32GB RDIMMs (or LRDIMMs)? It isn't clear to me what, if anything, a manufacturer has to do to enable support for extra-large DIMMs; is it just validation or are there hardware/BIOS changes required?

I'm asking this because I know a few years ago you couldn't actually buy 32GB DIMMs anywhere, meaning manufacturers "added" support for them at a later date. I know this was done in some cases without shipping new hardware revisions, meaning at most it was a BIOS update. What's not clear to me is if such a BIOS update actually did occur or would actually be necessary.
 

trents

Senior Member
Joined
Dec 27, 2008
Okay, I misunderstood your original question. Will the computer work with modules inserted that are larger than specs indicate? In my experience if the computer still boots with the out of spec-sized modules then you will be okay and be able to use them without issue but maybe not have all of it actually available or you will lose dual channel mode or something like that. There are also other issues such as single-sided and double-sided, low density and high density that can create problems when using non specked modules but those kind of issues usually create a non bootable machine.
 
OP
zachj

zachj

Chainsaw Senior
Joined
Aug 19, 2002
Location
Redmond, Washington
And that's generally my belief as well, but unfortunately I don't possess a 32GB DIMM that I can test with and I don't really want to buy one and then get stuck trying to return it to the store. Maybe I need to go bone up on Newegg's return policy :eek:

In this particular case, I'm also struggling with the fact that I don't actually know which type of module is more likely to work...I believe an RDIMM would generally have a better chance of working in my particular motherboard because the manufacturer doesn't have any LRDIMMs on the supported memory list, but then that exposes me to "organization" risks (ex: double-sided, high density, etc.). However, it's my understanding that a 32GB LRDIMM presents itself to the host like a 16GB RDIMM--which I know is supported by my board--so that makes me think maybe the LRDIMM is the better one to test even though the manufacturer doesn't list any supported LRDIMMs for my board.

So then I have to buy both types of modules to test? Ugh...
 

Johan45

Benching Team Leader Super Moderator
Joined
Dec 19, 2012
I would think the BIOS would need to support the HW
 
OP
zachj

zachj

Chainsaw Senior
Joined
Aug 19, 2002
Location
Redmond, Washington
I would think so too but it's just a gut feeling on my part...do you have a technical explanation to substantiate my gut feeling?
 

trents

Senior Member
Joined
Dec 27, 2008
zachj, you already created a thread asking this same question over in General. Multiple threads dealing with the same issue created by the same person in different areas of the forum is considered poor forum etiquette.

Mods, let's look at combining these threads.
 

EarthDog

Gulper Nozzle Co-Owner
Joined
Dec 15, 2008
Location
Buckeyes!
If you would like to suggest a thread move or combining, report it. Otherwise, we have to run across the thread to see it. ;)

I've merged the threads which creates a small chronological mess, but all the information, since it is intimately related, is in one post.
 

Mr.Scott

Beamed Me Up!
Joined
Jun 9, 2013
I know for a fact that HP lists the Z420/Z620 as not supporting 32GB DIMMS (neither LRDIMMs nor RDIMMs). But just because they're not supported doesn't mean they don't work...

Hence my question: what's actually required for 32GB DIMMs to function (whether officially supported or not)?

Thanks
Zach

Don't confuse unsupported with untested.
If a manufacturer says unsupported, that means they're unsupported, for whatever reason. They would not say this outright if they didn't try them.
If they didn't try it, they would say untested or simply n/a.
 

caddi daddi

Godzilla to ant hills
Joined
Jan 10, 2012
if I remember correctly, the cpu moves stuff to and from the memory and if that's the case I would only write a bios that fit the cpu memory specs and there has to be a hardware cost to moving that bandwidth around the motherboard.
 
OP
zachj

zachj

Chainsaw Senior
Joined
Aug 19, 2002
Location
Redmond, Washington
Well I finally decided to pony up the dough and test it...I can confirm that the generation 2 HP Z620--the one that supports Intel Xeon v2 processors--does support 32GB DIMMs...specifically, I tested these:

M393B4G70BM0-YH9
4Rx4 PC3L-10600R 1333 1.35V ECC REG
https://www.samsung.com/semiconductor/dram/module/M393B4G70BM0-YH9/


These are not LR-DIMMs (load-reduced); these are traditional registered ECC, but they're quad-ranked using Samsung's "dual-die package" memory that essentially combines 2 DIMMs onto a single module. Be warned that I have not evaluated what happens if all DIMM slots are populated with 32GB DIMMs, and I expect it may not work; what I know for sure is that you'd get reduced memory speeds if you populate more than one DIMM per channel.

Obviously HP doesn't certify these for use on the Z620 (nor even on the Z820 for that matter) but I can confirm that they work.

For anyone wondering why I would want to do this: a single dual-socket Z620 workstation makes a wonderful home virtualization lab once it's loaded with 256GB of RAM, and it's dirt cheap on eBay. It's roughly equivalent to an HP DL360 Gen8 but in a desktop form factor without the noise.

Thanks
Z
 

SamirD

Registered
Joined
Feb 24, 2018
Hate to bump an older thread, but in the interest of completeness of information for someone searching for it, I've got some additional information to add to the thread. :)

According to a post on the HP forum, someone else has also confirmed that RDIMMs do work, despite the fact that they are not expressly supported in the HP specs:
https://h30434.www3.hp.com/t5/Busin...O-work-on-z420-z620-workstations/td-p/7232654

I wanted to let the community know that I've installed 32GB RDIMMs in both the z420 and z620 and they *DO* work...Obviously the configuration is unsupported by HP but both Windows and ESXi have no problems with them. The only minor gremlin I've noticed is that populating 2 DIMMs/channel with quad-ranked DIMMs (as 32GB RDIMMs are) causes the system to ramp up the fans for 10-20 seconds before POSTing and it creates a bit of a noisy boot delay. But for a total of 256GB/384GB (z420/z620) of ram that's worth it! Be warned of the vagaries of Intel's support for quad-ranked RDIMMs on Ivy Bridge, though. Your memory speed will drop down to 800MHz, for example, and there's no workaround for that, so it's a tradeoff between large memory and fast memory. Note that I have *NOT* tried load-reduced DIMMs (LRDIMMs). They may work too, since they are officially supported on z820 workstations, but they'd be a similarly unsupported configuration from HP's perspective on the z420/z620. The advantage of LRDIMMs--if in fact they end up working--is that your memory speed would not drop to 800Mhz. So I think it would be worth somebody spending $75 bucks to try it out 🙂 Thanks Zach
In this post there is also a mention of LRDIMMs and the uncertainty of them working. Well, I happened to have some 32GB LRDIMM modules and may end up trying them as they haven't worked in my Dell R710 like I originally planned. I'll update this thread with the results if I do. :thup:
 

SamirD

Registered
Joined
Feb 24, 2018
Okay, so I'm here to confirm that 8x of the following 32GB LRDIMM modules work together for a total of a whopping 256GB of RAM. And this is with my 2011 version bios (the older one that doesn't support v2 processors): :clap:
hp 712384-081
samsung m386b4g70dm0-cma4qm
32gb 4rx4 pc3-14900L-13-12-c0

Other modules may work too, but these are what I'm running memtest on in my z420 right now. Caveats are the following:
  • Probably because of my 2630L cpu that only supports up to 1333 speed memory, this 1866 memory only runs at 1333 even when just one channel is populated. The good thing is that it runs at 1333 even with both channels populated. I would expect 1600 speeds with a faster processor like the 2650L or 2689.
  • Cooling may be an issue as during my first memtest, I noticed failures about halfway through. I opened the system to swap out the memory for another set and noticed that the modules in the sockets between the cpu and drive cages were scalding to the point I couldn't touch them. The cpu heatsink and memory with the fan on it were fine. And this is with the thermal management idle on the fans set to be floored, so even at maximum airflow, when the memory was stress-tested I believe heat caused them to start to error out. I have placed another fan in the system blowing directly on the first bank and am repeating the memory test on the same set of memory--hopefully this time all goes well.
There you go folks, 256GB in a regular nondescript cpu tower that when coupled with a nice 6-8 core cpu and populated with a bunch of drives makes a nice compact VM machine + nas in just one unit. :thup: