Help me understand this ram rank compatibility table please

[tJuggernaut29]

I am looking to buy ram for a Gigabyte G292-Z20 server with Epyc 7K62 cpu

 

Here is the rank compatibility table from the manual. 

My brain is too smol to understand this. please help.

 

 

So I know Micron 16GB DDR4 3200 2Rx8 ECC sticks are supported, because the server builder quoted them. However I am looking to use 32GB dimms

 

Would a 32GB DDR4 3200 PC4-25600 ECC REG RAM 2RX4 stick be compatible per this table? I am not understanding how to read the table.

 

thanks! =]

 

The 16 dimm slots on the server are labeled like this if this helps at all

P0_DIMM_A0

P0_DIMM_B0

P0_DIMM_C0

----

P0_DIMM_H0

 

P1_DIMM_I0

P1_DIMM_J0

P1_DIMM_K0

----

P1_DIMM_P0

 

manual [page 32]

https://download.gigabyte.com/FileList/Manual/server_system_manual_g292-z20_z22_e_1.0.pdf?v=0c1b197e601cac96ea882b926471dfac 

 

[Eigenvektor]

Here's my interpretation of the table, though I'm not 100% sure I'm correct.

 

From what I can see, the board has 16 slots and supports 8 channels. This means you can either have one or two memory modules per channel. When the manual talks about "DIMMs Populated", I assume they are talking about DIMMs per channel. So "1 DIMMs Populated" means 1 memory module per channel, or 8 memory modules total. From which follows that 2 DIMMs Populated would mean 2 per channel or 16 modules total.

 

For 3200 MT/s, you can only have one memory module per channel, or a total of 8 memory modules and it is possible with RDIMM or LRDIMM, but not 3DS RDIMM.

 

When you're using RDIMM, 3200 MT/s is only possible with 1 module per channel (i.e. 8 modules total) and the modules must either be 1R, 2R or 2DR. When you're using LRDIMM, you can also only have 1 module per channel or 8 modules total. You can either use modules that are 2S2R, 2S4R or 4DR.

[tJuggernaut29]

1 hour ago, Eigenvektor said:

When you're using RDIMM, 3200 MT/s is only possible with 1 module per channel (i.e. 8 modules total) and the modules must either be 1R, 2R or 2DR. When you're using LRDIMM, you can also only have 1 module per channel or 8 modules total. You can either use modules that are 2S2R, 2S4R or 4DR.

 

So for RDIMM the 1R or 2R is all that matters? the x4 x8 or whatever doesnt mean anything?

 

thanks

[Eigenvektor]

55 minutes ago, tJuggernaut29 said:

So for RDIMM the 1R or 2R is all that matters? the x4 x8 or whatever doesnt mean anything?

From what I could find, the X4 essentially tells you how many DRAM chips there are per module. My guess would be that the board as such doesn't care how many there are. Based on this post, X4 should have better performance than X8, which has better performance than X16.

 

2RX4 means there's two ranks, where each chip has a 4 bit wide data-bus. Since a rank has a 64 bit wide bus in total, that's 64 / 4 = 16 chips per rank, or 32 in total (+extra for ECC). And supposedly more chips = faster (and probably more costly)

 

(~edit: not entirely sure if this is related to the Single Die-Package (SDP) and Dual-Die Package (DDP), but apparently DDP often implies X16 - https://forums.anandtech.com/threads/dual-die-vs-dual-rank.2597797/)

 

Here's a more technical explanation: