SPD information incomplete, Lenovo Thinkstation C20 Dual-Processor

[c20]

I’ve recently acquired a Lenovo ThinkStation C20 (4263) system (Intel Tylersburg 5520).

The dual-processor mainboard is equipped with six identical 4 GB RAM-Modules.

 The OS w10 pro x64 (10.0.15063.413 (Win10 RS2)) indicates 24 GB of Memory.

 

AIDA64 indicates 24 GB of Memory in the Memory Tab, but the SPD information lists 12 GB (3 of 6 RAM-modules) only.

May I ask if this is a bug or a feature?

[Fiery]

Sadly, most 2-way and 4-way server motherboards use a SMBus mux to handle the SPD for more than 8 DIMM slots.  Such muxes are proprietary and not documented at all, so we can only support a few of them where we somehow could obtain the technical guidelines on handling the mux.  I'm afraid we have absolutely no such information on any Lenovo server motherboards though, so we can only support them without handling the SMBus mux.  It usually manifests as AIDA64 being able to detect half or 2/3 of the installed memory modules -- exactly as it is in your case.

[c20]

54 minutes ago, Fiery said:

Sadly, most 2-way and 4-way server motherboards use a SMBus mux to handle the SPD for more than 8 DIMM slots.  Such muxes are proprietary and not documented at all,...

Thank you for your reply.

Finally I've got an explanation, even if there isn't any solution to expect.

[Fiery]

35 minutes ago, c20 said:

Thank you for your reply.

Finally I've got an explanation, even if there isn't any solution to expect.

We can implement any mux, as long as we get the technical guidelines on it.  In case Lenovo is willing to help us out about that, we'd be happy to add a mux for your motherboard.  It's a discontinued product, so if you ping the right person at Lenovo, there's a chance they figure there's nothing wrong handing out such details on an old-ish product...

[c20]

2 hours ago, Fiery said:

 It's a discontinued product, so if you ping the right person at Lenovo, there's a chance they figure there's nothing wrong handing out such details on an old-ish product...

The 2 groups of memory slots are assigned to a single CPU each. Currently I presume that only the SPD of the 1st CPU is recognized.

Are you sure this is really a Lenovo issue or might it be a limitation of the Intel Tylersburg 5520 chipset? If Lenovo had followed an Intel reference design the Information needed might already have been published by Intel.

Simpler question: Are there other 5520-dual-processor-mainboards, where AIDA64 is able to read all SPD Information (e.g. https://ark.intel.com/de/products/36599/Intel-Server-Board-S5520HC )? 

[Fiery]

It is rooted in

17 hours ago, c20 said:

The 2 groups of memory slots are assigned to a single CPU each. Currently I presume that only the SPD of the 1st CPU is recognized.

Are you sure this is really a Lenovo issue or might it be a limitation of the Intel Tylersburg 5520 chipset? If Lenovo had followed an Intel reference design the Information needed might already have been published by Intel.

Simpler question: Are there other 5520-dual-processor-mainboards, where AIDA64 is able to read all SPD Information (e.g. https://ark.intel.com/de/products/36599/Intel-Server-Board-S5520HC )? 

It is rooted in the limitation of the chipset, since it can only handle up to 8 DIMM slots by default.  So the SMBus mux is necessary to make sure it can handle up to 16 DIMMs slots (using a 2-way / binary mux).

The SMBus mux of Intel S5500BC, S5520HC, S5520SC and S5520UR motherboards are handled by AIDA64.  Rare exception, but it's there.  The mux of a few Asus and Supermicro motherboards are also handled.