Is 2 x 8 GB RAM faster than 1 x 16 GB RAM ?

spapakons said:

Nowadays RAM is too fast to notice any difference between single channel and dual channel configuration. In the first DDR modules the difference was more obvious. Even if the difference is small, why not.

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Mostly correct but you will notice a difference if you play high end games with integrated graphics. Especially if it's an AMD system. With dual channel, you are doubling the speed of your video memory which makes a big difference.

This seems pretty much what i expected.
Normal bob who uses his pc as a browser and doesn't even know how to monitor usage on his pc isn't gonna 1. Care or 2. Notice

Anyone building a system for gaming or even just a high end rig, theres just no need to go for 1x.

Dual modules usually cost a little more than buying two single modules. If you cannot afford a dual module kit, buy a single large module so you have an available slot for future upgrade. It is preferable than buying a small capacity dual kit. I would rather buy a single 16GB module or a 2x 16GB kit. Buying a 2x 8GB kit is not cost-effective as a future upgrade would be 8+16 or you would have to replace the 2x 8GB kit with a 2x 16GB kit. In both latter cases you would replace at least one 8GB module.

The main reason to buy memory in pairs is because of matching - you can buy sets from different sources and as long as they, and the motherboard are designed and constructed for Dual Channel RAM they will work as a dual set.

It's better to get matching sets to reduce manufacturing variation between brands.

Dual channel RAM, theoretically, gives a much better bandwidth so improves speed of data throughput.

You also have to be aware that most motherboards will have a positional requirement so in a 4 slot motherboard the dual channels are slot 1&3 and/or 2&4 this also gives better cooling airflow when just two modules are fitted.

Dual channel RAM is at present at the start of being replaced by 4 Channel (or Quad) Ram - although I have read that current Quad Setups are not as good as they theoretically could be so best to research well and probably wait a while

Note
Most of the better system builders know what they need to do to properly match Dual Channel RAM, as an example I recently decided to up the RAM on my desktop so contacted my builder to order two 16GB modules to add to my existing 16GB modules. the technician said not to go that way due to matching issues - He offered to take back the two existing Ram Modules and replace them with two New 32GB modules - And charged me for the two matched 16GB Modules I had requested,

So I now have 64GB of Dual Channel Matched RAM and two empty slots for future use If I need to go to 128GB

You were lucky that you returned the old modules. Normally you would either combine the old and new modules or replace them wasting the money you paid for the original set. Dual channel works with mixed capacities, as long as all modules are of the same frequency and each pair is of the same capacity. Although the ideal would be to maximize capacity by installing 4 same capacity modules. Regarding the quad channel, it might work with a BIOS update on compatible motherboards with 4 RAM slots if we install 4 same capacity modules. Keep that in mind and have a look at manufacturer's support site for suitable BIOS.

jvickers said:

Quick question, Ghot. Assuming that you have 2x16 3200MHz in your system and want to add 2x8 more or 2x16 more, aside from ensuring that they're the same MHz, should you get pairs that match, or can you use any matched pair in the other two slots? Often, they'll discontinue a certain RAM chip, so you're left with purchasing a different pair. I've never really given this much thought until seeing your post here.

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There are many other settings that should match, frequency is just one of those, There's Cas latency and others as well as voltage, rank etc. It depends on BIOS if it could adjust itself automatically or it lets you do it manually so both sets can work at same settings, Rare are BIOS versions that can adjust each module or set to independent settings. That's why it's always recommended to buy RAM in sets of 2 or 4. Some times even 2 of same modules bought independently will not work properly let alone when they are different. It seems that only systems with DDR3 were flexible enough to allow for mix and match in many cases.

My builder, is not cheap, (I no longer build systems myself, but have specified and built my fair share). What the builder does is they buy their Memory and match it down to the manufacturing batch number, not just the normal parameters, like speed and so on.

I have always bought memory in pairs, except when there was a short period when some old intel processors worked best with three modules

Dual channel works if you match frequency and capacity. Other parameters are configured automatically to match the slowest module.

spapakons said:

Dual channel works if you match frequency and capacity. Other parameters are configured automatically to match the slowest module.

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If lucky,much depends on BIOS.

spapakons said:

Nowadays RAM is too fast to notice any difference between single channel and dual channel configuration. In the first DDR modules the difference was more obvious. Even if the difference is small, why not.

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For common tasks, your are right. But there always are some people who demand the peak performance, like for video editing or especially in video games like online FPS. For them, even the unnoticeable difference for typical Office user, may be critical.

Although most High end Games and Video Editors will these days utilise the Graphics RAM for processing the Still Image processors (especially Raw Image processors), still rely on the Main RAM to calculate the Maths required to edit, Which was the main reason that I upped the RAM in my Desktop

I demand and always strive to have performance I paid for.

CountMike said:

If lucky,much depends on BIOS.

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To be honest, I have not done a mixed capacity dual channel since DDR2 era, so I don't know how good it works with DDR3 and DDR4 modules. In the past every time I did it always worked fine except one or two low quality motherboards that didn't. That's why I prefer well known brands and I avoid very cheap implementations.

With AIDA64's Cache and Memory benchmark, anyone can test the "actual" read and write RAM speeds in single channel vs. dual channel arrangements.

Run the Cache and Memory benchmark with the RAM installed in TWO channels, then rerun the benchmark with one of the RAM sticks removed, which coverts the computer to single channel.

The value of the AIDA64 Cache and Memory benchmark, is that the Memory benchmark shows the RAM read and write speeds directly.
The CPU or vid card or resolution or quantity of the RAM... don't factor into the results.
This benchmark just reads the RAM's speed, by itself.

This is the main reason I used AIDA64's Cache and Memory benchmark to compare single to dual channel speeds.

User mixing and matching RAM affects the "stability" of the RAM.
Single vs. dual channel affects the read/write speed of the RAM.

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And IF you think the total RAM quantity affects AIDA's Cache and Memory benchmark (it doesn't)... you can also use a set of two RAM sticks in a single or dual channel arrangement, by simply moving one of the sticks from say... channel B to channel A where the other stick is.

Generally, most motherboards have the channels set up (wired), as follows...

Counting away from the CPU, (to the right)... dual channel will be with the RAM sticks in slots 2 and 4, or slots 1 and 3.
Single channel would be with the RAM sticks in slots 1 and 2, or slots 3 and 4.

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The point here... is that anyone can use AIDA64's Cache and Memory benchmark to make these tests.





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For "stability"... use two stick, matched sets of RAM.
For "speed"... use dual channel rather than single channel.

For the best of both worlds... use TWO stick matched sets of RAM in dual channel arrangement. :)

If you cannot afford maximize your RAM (buy a 2x 16GB kit), it is better to buy a single 16GB module now and match it for dual channel later, than buying a 2x 8GB kit. I don't like having to replace my modules at the next upgrade, while having a single module at start I can buy another module to do dual channel later.

spapakons said:

If you cannot afford maximize your RAM (buy a 2x 16GB kit), it is better to buy a single 16GB module now and match it for dual channel later, than buying a 2x 8GB kit. I don't like having to replace my modules at the next upgrade, while having a single module at start I can buy another module to do dual channel later.

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Put it this way, i've got 2x8gb sticks just now, Sometime im sure il upgrade to 32gb, Im just gonna be buyin another 2x8gb modules same of what i have, Done it before with no issues, Will do again

There have been a few reports lately of Memory manufacturers using lower density Memory chips on the modules due to the recent cost spike for the chips, This could mean that even buying Modules sold as exactly the same could be different enough to give a performance hit

If you ever had need to add extra modules take extra care to fully match the specs

The above density issue can also apply to NVMe Drives so be careful with these too