How do I count memory chips on the GTX960 128-bit 4GB before there is no way back? [warning:deep technical dive]

magicdark1337 · Oct 29, 2015

Disclaimer : this post might contain some deep technical "things" which may be unsuitable for youngsters; it also can contain strange humor, which may be unsuitable for adults, or might not be considered as humor
Hello folks,

I am collecting bits and pieces of information out of programmers curiosity + I plan on building a humble gaming machine;

I am looking at gtx 960 oc 4gb version, and there is a slight moment I am stuck/puzzled at:

Card's memory bus width is 128 bits => 4 'lanes' by 32bit => if they do use 4x1gb chips it's okay for me;
<hardcore>
But if they are using a single lane and attach two 512 mb's on both sides of card, hence placing 8 x 512mb chips on the 128 bus, I consider it's not okay. Since in theory it would gradually cut the bandwidth twice @ 2~4gb load (I know such load is slightly improbable but lets assume it happened), right? Generally speaking I would buy "a 2 gig card with blackjack and gradually even more useless 2 additional gigs". (It's like you buy a pair of boots, and they give you another one free, but the free one is ugly as an ugly duck, and even if you put it on, it would be quite an unpleasant voyage).
</hardcore>

I poked around google here and there but didn't really find a thorough review that would actually go this deep, and only found photos of front side of the card.

You have any ideas/suggestions how I could check before I buy it, rip it out of the box and the seller won't talk to me any more should I become unsatisfied with what I saw?

Pardon my non-native English [strike]speech[/strike] text,
also I'm sorry if your wife lol'd hard while reading about buying boots

cst1992 · Oct 29, 2015

Why do you think that the memory bandwidth will be lower if the chips are on both sides? The only thing I have seen reviewers saying is lack of cooling on the back chips if the card has no backplate.
Other than that, I don't think you need to worry.

magicdark1337 · Oct 29, 2015

cst1992 :

Thank you for your reply.

I think the bandwidth will gradually drop in this scenario:

Lets say these are memory chips:
[0] , [2] , [4] , [6]
[1] , [3] , [5] , [7]
The chips are connected vertically, so 0-1, 2-3, 4-5, 6-7 are on the same 32 bit "lane".
When the load is 2 gb, it would mean that chips 0,2,4,6 are filled to the max and consuming a single lane each.
Now lets say my load increases by 512 mb, and it goes to chip 1.
Chips 2,4,6 still use a full "lane", but 0 and 1 are sharing the lane, so if I suddenly request data from these two, it would take twice the time to transport it.

So gradually filling to 4 gb all lanes become shard and therefore theoretical bandwidth drops twice.

cst1992 · Oct 29, 2015

I don't know exactly, but it's a multilayered PCB.
The card may as well have 8 16 bit-lanes, and a 2 GB load may be stored as 256 MB on each chip for most available bandwidth.
Someone more knowledgable will be able to tell you better.

hang-the-9 · Oct 30, 2015

magicdark1337 :

You are WAY overthinking things, and not only that you are using guesses and assumptions without actually knowing how the memory in the video card works or is connected together.

To use your boots example, you are looking at boots, and saying they are cheap and not comfortable from 50 feet away without actually knowing what they are or how they fit.

Memory chips don't "fill" like buckets do and overflow into the next one for one thing.

magicdark1337 · Nov 4, 2015

hang-the-9 :

Thank you for your reply,
Please provide more information on how the memory in the video card works and/or is connected together, and in case if it doesn't really matter, why is it so

I may be way overthinking it, and of course I don't know some things therefore I'm here seeking knowledge.

The sole opinion about "overthinking" doesn't really help

hang-the-9 · Nov 9, 2015

magicdark1337 :

You need to look for some technical documentation on the specific card you are looking at for any details about how the memory would work. Usually the presentations at or prior to release that vendors do for tech journalists contain some details about the layout and architecture of the card.

This has a bit of info but there does not seem to be any details about how the full thing works, which is not surprising as companies would not want too many details about the products out there so competitors can copy them. http://www.anandtech.com/show/9547/nvidia-launches-geforce-gtx-950-gm206-the-lesser-for-159

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How do I count memory chips on the GTX960 128-bit 4GB before there is no way back? [warning:deep technical dive]

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