RAM upgrade: single rank vs dual rank (1Rx8 vs 2Rx8)?

[StevenQC]

Hi!

Want to add second stick of RAM in my new Omen 30L, so I can have 32GB instead of 16GB for MS Flight Simulator 2020!

I ordered a RAM stick from Amazon that matches capacity, speed and brand of the pre-installed RAM stick . BUT... one parameter doesn't match:  it is 1Rx8 (single rank) instead of the 2Rx8 (dual rank) of the pre-installed RAM.

I'm having a hard time finding infos online (including HP product page) about wether it is ok to mix 1Rx8 with 2Rx8 in Omen systems in particular, and also in general... Moreover, most of the matching RAM sticks I found in online stores seem to be 1Rx8, at least for "non-unavailable" single sticks (not sold as a pair)... 

Do I have to return my 1Rx8 RAM stick and get a 2Rx8? Maybe from another brand? Maybe matching the rank number (2Rx8) is more important than matching the brand?

Current pre-installed RAM in my Omen 30L (AMD):

Kingston HyperX Fury 16GB 3200 2Rx8

The RAM stick I ordered on Amazon: 

Kingston HyperX Fury 16GB 3200 1Rx8

P.S. I know about the RAM speed that steps down to 2166 or something like that, because of the XMP thing being locked by HP, but that's another problem with its own solution!

Thanks in advance!

[itsmyname]

Have you tried the new RAM by itself in your computer?

Have you tried the new RAM with the current RAM in your computer?

If your motherboard supports the higher-density "1Rx8" RAM, it should support the lower-density (twice as many memory chips on the stick) "2Rx8" RAM in a "mixed" environment.

But, if you are a belt-and-suspenders kind of person, you probably want to avoid "mixing" the RAM.

[DGroves]

you CANNOT mix ranks in a memory bank

A single-rank DIMM has one set of memory chips that is accessed while writing to or reading from the memory. A dual-rank DIMM is similar to having two single-rank DIMMs on the same module, with only one rank accessible at a time. A quad-rank DIMM is, effectively, two dual-rank DIMMs on the same module

to further explain,  most consumer motherboards have 2 or 4 dimm slots and if you read the manual you will see that most modern boards with 2 dimm slots are dual channel (each slot is one memory channel/bank) so in this case each bank can use different rank dimms

however some boards with 2 dimm slots are single memory channel, and each slot is part of the same memory bank/channel

in this case mixing dimm ranks will not work

boards with 4 dimm slots are usually  dual bank/channels and are labeled like A_1 A_2 / B_1 B_2

the 2 a slots are one bank and the b slots are another memory bank so you could populate slots a with 1 rank dimms and slots b with 2 rank modules you can not for either bank (A/B) mix dimm ranks

boards with 8 dimm slots are usually QUAD memory controllers

there are exceptions to the number of slots/banks, and these exceptions are usually usually found in servers/workstations

https://www.crucial.com/support/articles-faq-memory/what-is-a-memory-rank

[StevenQC]

Thanks Itsmyname!

Well I haven't yet unboxed my new RAM because I'm too busy reading responses to my interrogations about it on a couple of forums!

And I'm trying to get more info from HP themselves about my motherboard and if it supports 1Rx8 RAM sticks or not... because in the documentation for my Omen 30L it only says this:

• Dual channel (1 DIMM per channel) memory architecture.
• Two DDR4 UDIMM (288-pin) sockets.
• Supports up to PC4-25600 (DDR4-3200).
• Supports 8 GB and 16 GB DDR4 UDIMMs.

So basically you're saying that if I install my 1Rx8 alone in my system and it works, that will mean that it will work also when mixed with the pre-installed 2Rx8? 

And how do I test RAM in a extensive definitive way (I wouldn't want a BSOD that gets triggered from faulty RAM support just in certain situations not yet tested...!)

Well thanks again!

[StevenQC]

Hey thanks DGroves!

I re-read the documentation for my Omen 30L and based on what you're saying, I guess it should work?! You say that if the 2 RAM slots are "dual channel" (which they are}, then it means I can mix 1Rx8 with 2Rx8 (a 1-rank DIMM in 1 slot + a 2-ranks DIMM in the other slot).

Here's what the documentation for my Omen 30L says:

• Dual channel (1 DIMM per channel) memory architecture.
• Two DDR4 UDIMM (288-pin) sockets.
• Supports up to PC4-25600 (DDR4-3200).
• Supports 8 GB and 16 GB DDR4 UDIMMs.

So I guess it will work? 

But then would it run at an optimal performance? Or would the performance be better with same rank numbers on both RAM slots (two 1Rx8 sticks OR two 1Rx8 sticks)? 

And if so, would two 1Rx8 sticks be better? OR two 1Rx8 sticks?

So many questions! Thanks again!

[DGroves]

again,..........................you can not mix dimm ranks in a memory bank (simple as that)

how many memory banks and dimm slots per bank differs on various motherboards read the service/user manual for your system to determine the number of mem banks the board has

http://h10032.www1.hp.com/ctg/Manual/c06592761.pdf

again,.................rank is simply how the dimm chips are organized on the dimm module

[itsmyname]

Note that "dual-channel" mode takes each byte of data being written to the RAM (or read from the RAM) and writes "half" of each byte to the first stick, and the other "half" of the byte to the second stick.

So, instead of the elapsed time (we're talking microseconds) of eight "pulses" to write 8 bits to one stick, we have only 4 "pulses" per stick, done in "parallel", which obviously makes the transfer of the one byte much faster.

To achieve "dual-channel" mode, you need two "identical" sticks of RAM (same capacity, same speed, but not necessarily the same manufacturer).  At the time of the POST (Power On Self Test), the motherboard checks the two sticks of RAM, to see if the qualifications for running in "dual-channel-mode" have been satisfied. If not, then the two sticks run in "single-channel" mode. 

So, YES, you can use "mixed" RAM in the two slots, but the computer will operate the RAM in "single-channel" mode.

Note that many sticks of RAM will operate at slower speeds, in addition to operating at their "rated" speed. So, if you have one stick that is rated at "2400" and one stick that is rated at "3200", the motherboard is very likely to run the "3200" stick at the slower "2400" speed. 

Use the free SPECCY utility to examine the RAM. The "SPD" (serial presence detect) tiny chip on the stick of RAM will list the rated speed of each stick, plus the slower speeds that the RAM is capable of using. SPECCY will also report whether the computer is using "single-channel" or "dual-channel" mode.

[StevenQC]

Hi DGroves,

You said "again,..........................you can not mix dimm ranks in a memory bank (simple as that)"...

Ok, well the documentation for my Omen 30L & it's motherboard mention that the 2 RAM slots are dual channel architecture, BUT... it doesn't mention anything about the "banks"... How can I know if the 2 slots are one bank or 2 banks??

Based on what you said, without knowing the bank configuration of the 2 slots, I can't know if I can mix a single-rank DIMM with a dual-rank DIMM... Is that so? Sorry if I'm missing something obvious or something, I'm new to the concept of RAM banks...!

Thanks again!

[StevenQC]

Hi Itsmyname,

If I understand correctly, in order for the RAM to run in dual-channel mode, the 2 sticks of RAM need to be identical, BUT... "identical" here means each stick needs: same capacity, same speed, (not necessarily the same manufacturer), AND SAME NUMBER OF RANKS... is that right? "Same number of ranks", that's the part that is almost never mentioned in articles or how-to-videos about RAM upgrades... why is that?

Ok so the best for me is to return my 1Rx8 HyperX Fury stick, and try to find a 2Rx8 version, so it can be mixed with the pre-installed 2Rx8 in my Omen, and it would run in dual-channel mode then.

Cheers,

[DGroves]

your manual does tell you..................... it says Dual channel, and has 2 dimm slots so therefor each dimm slot is a single bank

IE- you have 2 banks of ram, using a dual channel memory  controller if you insert different ram sizes or different rank dimms the system "should" boot but will be running in single channel mode instead of dual and only have 50% of the memory bandwidth of dual channel  although the total ram of each module will be seen/useable