T7810 - Mixing RAM Question (2Rx4 and 2Rx8)

• Memory modules of different sizes can be mixed (for example, 2 GB and 4 GB). But, all populated channels must have identical configurations. • Memory modules must be installed beginning with the first socket. NOTE: Registered DIMMS (R-DIMMs) and Load Reduced DIMMS (LR-DIMMs) cannot be mixed. • If memory modules with different speeds are installed, they operate at the speed of the slowest installed memory modules. NOTE: If all DIMMs are 2133, the CPU ordered may run the memory at a slower speed.

T7810 Owner's Manual.pdf

Precision T7810 Spec Sheet

The above is pasted from pg. 34 of the owner's manual.

If using non-Dell memory,.Crucial is highly recommended as it's guaranteed to work in Dell's.  Kingston Value Brand (KVR) almost never works.  Volts can be off in off-brands causing further problems.  Make sure brand name and MHz are still the same.

Right ... I did see that part in the manual. But this question is a bit more specific :). It isn't an issue of size it is about slightly mismatched specs on the data-bus width especially because how ECC works is different between 2RX4 and 2RX8. I'm just not sure if the motherboard/bios will adapt to it.

Hi @Niren ,

Thank you @bradthetechnut calling me out for this post. Let's break down your questions:

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So, I was thinking of getting 2 X 32GB to add to the system

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I'm afraid not. Page #53 on the owners manual stated "Memory module capacity: 4 GB, 8 GB, and 16 GB" only.

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So, the question is if this configuration is supported -- i.e. mixing 4 X 2Rx8 and 2 X 2Rx4 chips.

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Many discussion on this topic as most user guides and manuals emphasis only on matched memory type (e.g. UDIMM, RDIMM, LRDIMM, etc.) or rank (e.g. dual rank, quad rank, etc.) but not data-bus width (e.g. x4, x8, etc.). In fact, it should be fine provided that memories with same data-bus width installed in pairs on the same DIMM channel. Several discussions as listed below for reference. 

• Mixing 2Rx4 and 2Rx8 DDRIII Memory DIMMs
• r720XD mixing 2RX4 with 2RX8?
• T620 mixing 2Rx4 & 2Rx8 DIMMs

It isn't an issue of size it is about slightly mismatched specs on the data-bus width especially because how ECC works is different between 2RX4 and 2RX8. I'm just not sure if the motherboard/bios will adapt to it.

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A Dell moderator explained in this thread that "The x4 & x8 refers to the number of banks on the memory component or chip. The higher the number of banks, the fewer the chips in the memory module, the better the reliability and power consumption. Our servers support mixing memory modules of different Ranks and number of banks."

Lastly, if you want to know more about data bus width, you may read on this article.

Hopefully information above helps.

You're welcome.  And that's true for pgs. 35 & 53 of the manual.  So it's either a typo or missed info an pg. 53.

I have a question. Im using dell g3 3579 and i want to know if it is okay to mix 1Rx8 and 1Rx16 in the two slot of rams on my laptop. My stock ram is 1Rx16 and i cannot find online with that bank size but i can find ram with the same brand, speed and latency, and the only problem is it is 1Rx8. Can i mix it? 

I was notified by Dell directly today that the G series are rebadged enhanced Inspirons.  So, for now, until new categories are added, G series should be posted in the Inspiron forums.  Inspiron Laptops