single and dual bank in laptops

zalazin

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I have an HP i5 10210u with 32 GB of ddr 4 both dual bank crucial sodimms one a 2400 the other 3200. Machine runs perfectly fine but at 2400 the slowest memory rule. The mobo on this laptop is rated for 2666 mem. Well I picked up a PNY 16GB 2666 single bank sodimm and removed the 2400 one. The machine did run at 2666 but performance actually dropped about five percent and is sluggish, Why? is it because of the single bank sodimm..? i put the 2400 dual bank back and perfomance returned....
 

Shikami

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Dual ranks will always be a better choice. It can get complicated though in the way that some measure "performance" of memory; and even more complicated with particular topologies and VRM support that cause lower clocking. With your previous memory 2400 to 2666, there was only a 33MHz mem clock and a 133.33 I/O clock difference. The CAS latency are all very similar between the two. Not much of a gain for the cost when measuring clocks. However, ranked RAM has a nice trick.

The memory controllers are, basically, an aggregate of two separate regions mapped to each controller-. With most desktop processors we have two 64bit controllers that each have a mapped area they work in. With 16GB DIMM installed in one bank, and a 16GB DIMM installed in another bank, it is easy to think of the mapped bottom of memory, and the top of memory. Lets say for ease without ranked RAM, it allows a read from one controller, and the other controller a refresh. Here is an example of all banks installed and interleaved: https://en.wikipedia.org/wiki/Interleaved_memory. Sometimes, when all banks have a DIMM installed you will have the controller "rank" the mapping for each installed bank. This was actually the old way of doing things that some Mac users may recall.

So, at least one cycle you are "losing" out and is really only 64bit at a time with single rank. Dual rank allows not only the two controllers to be interleaved, but also to interleaved with the ranks. It hides latency and increases over all interactions to RAM for more page hits. So, refresh one rank of the RAM, but read from the other rank on just one controller alone. The secondary controller you can write one rank, and refresh on the other rank. This is ping'ed-pong'ed around with both controllers and ranks of the RAM, both being interleaved. More dual 64bit controller like with dual rank isn't it? Usually the difference alone is around 5% when measuring (which you noticed), and usually all high end computers are ranked DIMMs, and even up to quad ranking with many servers.

To note, only one rank at a time is accessible. One rank is being accessed for data while the other rank is being readied for it. Some controllers have limitations to the ranking that they can address-this is usually server land.
 

BinarySynapse

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the crucial was 3200 CL 17, dual bank, pny was 2666 CL19 single bank

I mean what are the timing's they're actually running at? If the 2400 RAM was something like CL16 (13.32ns) and moving up to 2666 increases the timings to CL19 (14.5ns), that's a 7% increase in latency and could account for your overall 5% lower performance.
 

zalazin

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I mean what are the timing's they're actually running at? If the 2400 RAM was something like CL16 (13.32ns) and moving up to 2666 increases the timings to CL19 (14.5ns), that's a 7% increase in latency and could account for your overall 5% lower performance.
This whole thing sort of sounds like if you mix single and dual rank with the two sodimm sockets you sort of create a flex memory situation though not quite as bad......
 

zalazin

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Now I do have two 8GB samsung modules with a 1RX8 on the label, which according to google articles means it is single rank, Now will these two in dual channel give me full speed or will the single rank of both slow the perfomance down?
 

dasa

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You shouldn't be able to tell the difference between single and dual rank outside of synthetic benchmarks.
Run a memory benchmark before and after with something like AIDA64 or userbenchmark.
Results will likely be within margin of error unless you close down a heap of background processes.
 

zalazin

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I did all that if you check my posts... Its got to be something related to the rank thing. I originally bought the 3200 16 gb for my Zephrus G14 which has one single rank 8GB soldered on board with another single rank on a upgradable second slot. I knew installing the 3200 16gb would create a flex memory scenario . However I dropped in memory bandwidth from 50000 to 20000 on the Sandra memory bandwidth test.. more than than half. Now after what you posted and what I have read I understand why. Either all single rank or all dual rank.. Well I guess you learn something new every day....
 

Shikami

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I'm going to say, I don't think you can do Flex, unless you do have more than two banks. Laptops can have, but usually do not have much expansion plotted. Good theory, but Flex does allow dual channel if you had two symmetrical DIMM's and a third asymmetrical DIMM. For example, 8GB and an identical 8GB will be dual channel, and is called the symmetrical zone and is interleaved. A third asymmetrical zone top of memory 4GB DIMM will be single channel non-interleaved access. According to datasheets for SODIMM it is written: "There is no support for memory modules with different technologies or capacities on opposite sides of the same memory module. If one side of a memory module is populated, the other side is either identical or empty." So, you may be experiencing compatibility and support of the channels, and therefore see such a drop in bandwidth.

I just follow a few rules. 1, I try to get the datasheet for memory support: AMD a little difficult due to them not releasing the information (https://www.amd.com/en/support/tech-docs?keyword=&f[0]=tech_docs_document_type:data_sheets&f[1]=tech_docs_product_type:processor), Intel easier (e.g. https://www.google.com/search?q=int...i60l2j69i65.3684j0j7&sourceid=chrome&ie=UTF-8). 2, Motherboard and/ or RAM supplier QVL is what I follow. 3, I never go after much of the expensive non-compliant RAM because mostly bullshit not worth the cost, and unless you follow particular guidelines you may have issues (for example, procuring RAM that exceeds the VRM and abilities of the motherboard design). 4, Never-ever mix different chips and manufacturers, must purchase identical DIMM's 4, Always go for dual rank with desktops.

Your datasheet readings: https://www.intel.com/content/www/us/en/products/docs/processors/core/core-technical-resources.html
 
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