RAM QUESTION

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RAM QUESTION

Postposted on Sun Mar 02, 2014 5:34 pm

So I plan on posting a build over in that special builder's forum but before I do that I have a question/concern that I would appreciate some kind guidance on. I will be building for video editing and I am not sure exactly how much RAM I will actually need. I am getting at least a dual channel 16GB kit. The motherboard I will be getting will support 32 GB over a total of 4 slots. So with the high price of RAM I was considering getting a set of 16GB (8GB x 2) and a set of 8GB (4GB x 2) to total 24GB of ram for the computer instead of going with 32GB...

So what I would like to know is if having RAM set up like that is going to cause any kind of issues. I would buy the same brand of 1600 speed memory. I am assuming it would work just fine but I am not sure...
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Re: RAM QUESTION

Postposted on Sun Mar 02, 2014 6:00 pm

Unless you know specifically that your application requires an exact amount of memory in the range of 16-24 GiB, why don't you start with 2x8 GiB? If you find that an initial 16 GiB is not enough, then add a second 2x8 GiB kit for 32 GiB total.
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Re: RAM QUESTION

Postposted on Sun Mar 02, 2014 6:19 pm

That's what I was intending on doing I just wanted to know if mixing different sizes would cause any sort of an issue...
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Re: RAM QUESTION

Postposted on Sun Mar 02, 2014 6:46 pm

iamjsmith83 wrote:That's what I was intending on doing I just wanted to know if mixing different sizes would cause any sort of an issue...


Mixing sizes is generally not an issue, but you will lose some performance; If you have 8GB in one channel and 16GB in another channel, you will only have dual-channel memory bandwidth for the first 16GB, the last 8GB will perform at the single-channel speed, which may not matter for video editing.
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Re: RAM QUESTION

Postposted on Sun Mar 02, 2014 6:56 pm

I'm suggesting that you do not need to set out to mismatch your memory. Start with 2x8 GiB then decide if you want to add another 2x8 GiB. Choose either 16 GiB or 32 GiB total without worrying about the 24 GiB option.

$148 2x8 GiB PC3-12800 G.Skill F3-1600C9D-16GAR (DDR3-1600, CAS 9, 1.5 V)
$160 2x8 GiB PC3-12800 Crucial BLS2K8G3D1609ES2LX0 (DDR3-1600, CAS 9, 1.35 V, low profile)
$160 2x8 GiB PC3-12800 Mushkin 997110S (DDR3-1600, CAS 9, 1.35 V)
$165 2x8 GiB PC3-14900 G.Skill F3-1866C9D-16GSR (DDR3-1866, CAS 9, 1.5 V)

While it is generally possible to mix two different sizes of DIMMs, you may end up needing to run your memory at slower speed or with more relaxed timings than the XMP profiles call for just to keep your system from being unstable.
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Re: RAM QUESTION

Postposted on Sun Mar 02, 2014 7:12 pm

Chrispy_ wrote:If you have 8GB in one channel and 16GB in another channel, you will only have dual-channel memory bandwidth for the first 16GB, the last 8GB will perform at the single-channel speed


You can just put 12GB in each channel to avoid this, can't you?
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Re: RAM QUESTION

Postposted on Sun Mar 02, 2014 7:39 pm

Melvar wrote:
Chrispy_ wrote:If you have 8GB in one channel and 16GB in another channel, you will only have dual-channel memory bandwidth for the first 16GB, the last 8GB will perform at the single-channel speed


You can just put 12GB in each channel to avoid this, can't you?


If you have 12 GiB modules, it would be possible. But memory doesn't really work that. Its got to be binary based. 1,2, 4, 8, 16, 32, 64, etc.

You may be thinking in terms of triple channel, which would be a 4-4-4 setup, in three separate channels.
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Re: RAM QUESTION

Postposted on Sun Mar 02, 2014 7:57 pm

I have successfully configured a system to run with 12 GiB of DDR3 (2+2+4+4), but I will also tell you that a very tech-savvy user accidentally swapped the order of the DIMMs in that system and experienced erratic system crashes and lockups that he eventually blamed on a failed motherboard or memory. This was despite two tries at trouble-shooting DIMM installation order that I suggested over the phone. Once I got my hands back on the system, I was able to fix the problem by getting the DIMMs installed in the one configuration that works, but that was after wasting $$$ on a new 2x8 GiB memory kit that wasn't needed.

It's just much easier and more reliable to use two or four identical DIMMs. Start with 2x8 GiB. If that's enough, great. If it's not enough, you can pick up another 2x8 GiB at a later date.
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Re: RAM QUESTION

Postposted on Sun Mar 02, 2014 8:13 pm

Thanks a lot. I appreciate it.
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Re: RAM QUESTION

Postposted on Sun Mar 02, 2014 9:43 pm

TheEmrys wrote:If you have 12 GiB modules, it would be possible. But memory doesn't really work that. Its got to be binary based. 1,2, 4, 8, 16, 32, 64, etc.

You may be thinking in terms of triple channel, which would be a 4-4-4 setup, in three separate channels.


No, I'm talking about putting one 8GB DIMM and one 4GB DIMM in each channel. Both channels would have the same configuration so it shouldn't drop back into single channel mode. I'd personally not do this for the reasons JAE stated, but it should work.
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Re: RAM QUESTION

Postposted on Sun Mar 02, 2014 10:16 pm

I'm not sure which OS you're using, but keep in mind that the very popular Windows 7 Home Premium is limited to 16GB of RAM. The "Pro" variant does not have this limitation, nor does Windows 8.
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Re: RAM QUESTION

Postposted on Mon Mar 03, 2014 8:31 am

Melvar wrote:No, I'm talking about putting one 8GB DIMM and one 4GB DIMM in each channel. Both channels would have the same configuration so it shouldn't drop back into single channel mode. I'd personally not do this for the reasons JAE stated, but it should work.


I would advise against this too. Generally it's okay to mix RAM but as JAE has explained, you have to be careful with configuration, otherwise you can get instability.

Some chipsets will allow DIMM mismatches in a channel (so 4+8 in channel A and 4+8 in channel B), other chipsets will support DIMM mismatches but you have to keep all RAM of speed/timings in each channel (so 8+8 in channel A and 4+4 in channel B)

It's rare that you can't make it work (hasn't happened to me before and several laptop/workstation vendors ship machines with RAM mismatches) but it's often more hassle. Unless you're really penny-pinching, go for either 16GB or 32GB of RAM. 12GB or 24GB will save you very little money and it may make things harder by forcing you to do a BIOS update and fiddle with timings manually when it can't decide which SPD timings to standardise the FSB on.
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Re: RAM QUESTION

Postposted on Thu Mar 06, 2014 7:17 pm

firstly, I'm a newbie

just to answer your question in short form, no, the dimm setup in channel 0 and 2 does not need to match 1 and 4. (or some variation on that in the case of 8 slot motherboards) The first pair can be both a different size, and a different speed, than the second pair. But identical pairs must be used in a dual-channel supporting bank.

In the case that the rated ram speed (the "ram speed". this is just the best frequency and timing that is assured to you on a set) of the pairs do not match, all ram will be run at the best frequency and timing configuration of the slowest pair. sometimes, some ram will not like to run at a slower timing or frequency than it is advertized for, and this, I believe, is what causes the phenomenon of ram not working properly when you add two sets of different speed, in different channels. I believe this is the higher speed ram having trouble when it is run at a slower speed (which should not happen, usually this is an indicator of bad chips) more on this below. Also I am unaware if some BIOS' fail when they do not find a matching profile between the higher and lower speed ram, rather than just configuring the higher speed ram at the lower speed's specs. This could be them taking into account the previous problem about finicky sub-standard ram not wanting to downclock. and see here from wikipedia

"If the motherboard has two pairs of differently colored DIMM sockets (the colors indicate which bank they belong to, bank 0 or bank 1), then one can place a matched pair of memory modules in bank 0, but a different-capacity pair of modules in bank 1, as long as they are of the same speed. Using this scheme, a pair of 1 GiB memory modules in bank 0 and a pair of matched 512 MB modules in bank 1 would be acceptable for dual-channel operation."

"Modules rated at different speeds can be run in dual-channel mode, although the motherboard will then run all memory modules at the speed of the slowest module. Some motherboards, however, have compatibility issues with certain brands or models of memory when attempting to use them in dual-channel mode. For this reason, it is generally advised to use identical pairs of memory modules, which is why most memory manufacturers now sell "kits" of matched-pair DIMMs. Several motherboard manufacturers only support configurations where a "matched pair" of modules are used. A matching pair needs to match in:"


As with most things in the PC space, problems arise from cost cutting **** and marketing that is just a tiny bit away from outright lies, rather than with the actual spec stuff itself.

now if you're interested here is some extra information.

based on what I could find when I looked into this before. some of this stuff is to do with increased variation that isn't present anymore, nowadays with there being two memory controllers, largely, and everything pretty much defaulting to either 1600 or 1333.

In the early days of dual-channel, some of the dual-channel setups were ganged, and not truly independent. two 64 bit channel were ganged together, instead of two separate but synchronizing 64 bit paths. this was apparently evident on some AMD chipsets. this is not the case nowadays. there are two fully independent 64 bit channel wired and controlled to operate together as one. when you had the ganged setup, it was known to cause problems when you had mismatched ram pairs in different dual-channel banks. I think some of what it is talked about is a holdover from that era and time.

Also, it should be noted that on Haswell chips, Intel has implemented a new memory accessing scheme whereby you don't even need the capacity of the ram pair to match in one dual-channel bank. Intel calls this "Flex mode". And it basically uses the memory in dual-channel mode up to the limit of the smaller module, and accesses the rest of the larger module in single-channel. the larger must be in the first bank.

I'm not gonna say you should listen to me over these other fine folks that have experience I lack. but this was a subject I have done a lot of research on so I took the opportunity to collect my thoughts once more and in the process share I what I had come up with. no idea if putting say, your 16gb g.skills in one bank, then, your future 8gb [enter name here] in the second bank would cause the system to be unstable if the second pair didn't like the timings or frequency or whatever. or the motherboard wasn't built for this or such. but the spec says it's all good, any problems you might hear of, may not apply to today's cpu-memory relationship and standard of 1600. but I couldn't say. like was suggested, if you don't mind messing with your ram timings, then you could probably get it working, in the case that something screwy went on to prevent this from working as it otherwise has been designed. it is true that all identical is the safest bet with regards to this stuff.

references:

http://www.intel.com/content/dam/www/pu ... asheet.pdf "(section 2.1.3)
http://web.archive.org/web/201109290240 ... epaper.pdf
https://www.overclockers.com/forums/sho ... p?t=622173 (4th post)
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Re: RAM QUESTION

Postposted on Fri Mar 07, 2014 10:42 am

Having repaired/upgraded probably well over a thousand (maybe even two thousand) PC's from Dell/HP/Acer/Fujitsu/Lenovo or even home-brew builds the one thing I can say for certain is that no manufacturer is consistent.

HP/Dell/Asus will sometimes have completely different behaviour based on the model, BIOS revision, RAM type used and there can be component differences between to PC of the same model range.
It's rare that you can't make an imbalanced setup work at all, but you'll often have to do some hocus-pocus involving slower timings, using the correct DIMMs in the correct slots, and possibly even bios updates/rollbacks.

As you mentioned, what the specs and marketing blurb *says* the system can support doesn't always correlate with what happens in the real world - though the longer something has been on the market, and the more updates and revisions there have been, the closer the two things are to each other.

I think the key issue here is that a pair of 8GB DIMMs is better value than a pair of smaller 4GB DIMMs. If you already have the smaller DIMMs lying around spare, it's worth trying, but it's not worth buying smaller DIMMs to try and save money - that's just a false economy in the long run.
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