Xeon 8272CL Maximum Memory

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kellenw

New Member
Jan 15, 2022
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I have been researching this CPU and have seen numerous conflicting specs regarding the maximum memory supported by this CPU. Some say 1TB per socket while others say 4.5TB per socket. I'm hoping someone on here might be able to report real world experience with trying to push beyond 1TB on a socket and if it worked. Anyone? :)
 

NablaSquaredG

Layer 1 Magician
Aug 17, 2020
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If intels naming system is applicable for oems skus than it's a (L)ow power cpu...
No, it is not.

CL are most often the opposite of low power - they are usually 210W (/255Ampere) high power SKUs (like 8259CL, 8275CL, 8272CL, ...)
 

Stephan

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Apr 21, 2017
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8272CL means Cascade Lake Xeon (x2xx) and those have 1 TiB minimum. "C"-suffix is undocumented, possibly "custom(er|ized)", "L" suggests 4.5 TiB. "M" would be 2 TiB. That being said, you will need a huge board with 12-16 DIMM slots per CPU. One CPU has 2 memory controllers with 3 channels each, so best speed would be 6 DIMMs only, and only 32 GB RDIMMs at that. There is a benchmark somewhere that compared 16/32/64 RDIMMs, 32 GB came out in 1st place. If you up the game to 12x 128 GB LRDIMM per CPU, you will get to 1.5 TiB of RAM per CPU or 3 TiB total in a dual socket system. For Cascade Lake, that will be pretty much it. Also because 19" breadth limits how many memory slots can be crammed into the space next to the CPU sockets.

For Ice Lake Xeons (x3xx) there are 8 RAM channels for a possible total mainstream 2P system with 32 slots, 16 per CPU, and 32x128 LRDIMMs for 4 TiB in total.

Anything beyond FCLGA4189 with its whopping 4189 pads is running into mechanical stability and cooling issues in a 2U case. I suspect there will be a transit like with PATA to SATA or Ultra-320 SCSI 20 years ago to 4-lane twinax SAS.

That said you'd need a board which manufacturer has tested with that much of RAM. Don't build anything with RAM parts that aren't on the QVL.
 

RolloZ170

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Apr 24, 2016
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note there is a QS version of the 8272CL
this is the 8272L QS - the confidential is printed on the heatspreader, for that reason not in the brand string.
 

RolloZ170

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Apr 24, 2016
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What is the source of "Maximum Memory Capacity" number, something from DMI? Would want to check in Linux. Also since this could be part of a Multi Processor system, is this a per system limit or per CPU?
HWInfo / AIDA64 - register reading is not public (NDA)
 
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Stephan

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Apr 21, 2017
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HWInfo / AIDA64 - register reading is not public (NDA)
Anecdote: Needed socket P0 3647 pinout for troubleshooting a board-level issue in a project. Signal list is public, socket pinout is NDA. So I requested it. Months later, they sent sales reps and nothing else. Couldn't believe it. Then I saw $INTC share price. Now I am a believer.

Anyhow, thanks for the screen cap. These tools pretty much only source then.
 

Rand__

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Mar 6, 2014
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not even god knows.
Do you know if this is an actual limit or if this the limit that was possible with the dimm sizes available at the time?
I'll give you 5 bucks if you test it out for us - its only 18 256G modules, should be no problem, right?;)

The easier to reach 768G limit on Skylake was actually a hard limit... and Optane Memory counted towards it iirc, so I would think that this one is actually implemented too. Not too far off maybe with a bunch of 512G Optane modules...