Thinkpads Forum

All four sticks are Samsung, PC3-12800S, CL 11, 1.35v, the only difference is there is a matched pair of 8GB sticks installed now and a matched pair of 4GB sticks on the way. Does it make a difference how they are installed in the four slots? For now, the two 8's are opposite each other and are the ones a person sees when removing the cover, with two empty slots underneath them. According to Speccy they are in slots #1 and #2, but according to CPU-Z they are in slots #2 and #3. Does it really make a difference? TIA

Ideally the 8s and 4s would be installed in pairs in the same channel, for symmetrical dual-channel configuration. Asymmetrical dual channel is supported in many cases but doesn't offer a consistent speed for all memory addresses.

From what I can tell..... each color is a single channel. So you'd want the two 8s in the top so there's one in the white and one in the black slots, then mimic that for the bottom.

Thanks for the reply. I've removed the cover and the two 8GB sticks, and I need to ask you, where should I be looking for this black or white you mention? Sorry, but I don't see it?

Very possible it's just certain motherboards that have it? In any case each pair of slots - towards the front and rear - should contain one each of each memory channel.

Bookmark this: https://forums.lenovo.com/t5/ThinkPad-P ... a-p/249257
Should also apply to W520/W530/W540

I don't think it matters which slot.

My W540 has also 24GB, because I'm using 3x 8GB RAM modules, since one of the slot closing mechanism is slightly defective.

I can't remember though which one I left without RAM, I can take a look later when I'm back at home.

Another thank you to all who have responded to my original post. The more research I do into this search, the more confused I get. There doesn't appear to be consistent numbering of the slots. Depending on the software I use-CPU-Z, Speccy, HWiNFO64, or Crucial Scan, I might have the two 8GB sticks now in slots 2+3, 1+2, 0+1, or in a photo on the Lenovo forum labeled 1+4.

It would be funny if it wasn't so frustrating.

I moved the two 8's to the two slots opposite each other closest to the keyboard, and they're staying there until the two 4's arrive. They're working in dual channel mode, the last BIOS time as reported in Task Manager is about 6 seconds, and the laptop seems to boot the quickest that way.

@CharlieDog - I've just picked up a W530 and I'm trying to figure out the same thing. I'm having trouble understanding your "notation". For the sake of my understanding, could we call:

Slot 0 - the upper slot under the keyboard
Slot 2 - the lower slot under the keyboard

(That would be consistent with the numbering for the W520)

Slot 1 - the upper slot under the back memory cover
Slot 3 - the lower lot under the back memory cover

So which slots did you populate to get dual channel operation? You say, "... the two slots opposite each other closest to the keyboard ..." Are you saying slots 0 & 2? If so, that would be different from the 510/520 series, where it was one slot under the keyboard and one under the back memory cover. (See: https://forums.lenovo.com/t5/W-Series-T ... d-p/438611)

Also, maybe you could clue me in - how do we test for dual channel operation?

[Edit: I see that under Windows, CPU-Z will tell you, but I'm using linux.

Reading around the web, it seems the information is under `dmidecode -t 17`, and that the RAM slots are labeled A0, A1, B0, B1. So you want to populate opposing pairs with matched sodimm's, eg A0 & B0 is one pair and A1 & B1 is another. Sometimes A is called a "Channel" or "Bank", similarly for B. So you want to populate the same slot number in different channels. There is some indication that you should populate A1 & B1 first, and then A0 & B0. If populated in this order, and the MoBo supports it, then it will run dual channel. How to tell if the MoBo supports it, other than to check the hardware specs, I don't know. Benchmarking could tell you, but if there's a direct way through software, I haven't found it.

These two links helped:
https://superuser.com/a/1365754
https://www.reddit.com/r/linuxquestions ... s_in_dual/

I realize you are concerned with a W540, but I have W/T520's and W/T530's. I can't find the words "dual" or "channel" in the HMM's for any of these.]

This is what I determined by going one module at a time in a Quad core W530 made in Nov 2013:

I guess not all W530s are created equal.

And that Lenovo link (below) that details which slots are which number is also inaccurate, at least for my recent W530 system.

link: https://forums.lenovo.com/t5/ThinkPad-P ... a-p/249257

You still want to populate slots 0 & 1 first and then 2 & 3, but they are numbered different than before (or maybe newer ones are different than mine)

I have a 2441-CQ7 i7 3840QM Quad with 4 slots date 1311, 2013 Nov. It has two slots under the keyboard, staggered on top of each other as one would expect. It also has two slots on bottom under the memory door and these butt against each other. They are not staggered on top of each other as the ones under the keyboard.

I have two 4GB modules and two 8GB modules all the same speed PC3-12800 / DDR3-1600 It came with the two 4GBs under the keyboard and I bought two 8GB modules (and another two to max it out at 32Gb).

Here's where the fun part comes in. I'm using HWinfo and CU-Z. Since CPU-Z numbers the slots 1-4 I'll just use the HWinfo numbers since they are same as Lenovo's CPU-Z reports the same order but goes 1-4 instead of 0-3.

When I populated the slots as per the Lenovo link above, I got dual channel but the sizes in the slots were all wrong.

When I only populated what the link says was slots 0 & 1, I got single channel and the slot #s were not what I expected either. Populating the two under the keyboard only, gave dual channel but using slots 2 & 3! So I went to one module at a time and have determined that the following is the correct numbering:

The upper slot under the keyboard is #3
The lower slot under the keyboard is #2
The slot closer to the ultrabay is #1
The lower slot between the HDD and docking connector is #0

So I put both the 8GB modules on the bottom and the two 4GB modules under the keyboard and it now says slots 0 & 1 have 8GB each while slots 2 & 3 have 4GB each. This matched Lenovo's suggestion to have the largest modules in slots 0 & 1.

You can populate only the two under the keyboard and it will give you dual channel and it does not matter the size. I suppose the speed does matter, but all mine were the same speed.


I hope this clears up some confusion because I sure was!