Mixing and matching RAM

[itm]

Is it possible/advisable to mix RAM of different capacity?
So for example if a machine currently uses two slots, each containing 16GB Corsair Vengeance LPX DDR4 3200MHz Memory (total 32GB), could the other two slots be used for two 32GB sticks:

Corsair Vengeance LPX 64GB (2x32GB) DDR4 PC4-25600C16 3200MHz Dual Channel Kit (Black)

Order Corsair Vengeance LPX 64GB (2x32GB) DDR4 PC4-25600C16 3200MHz Dual Channel Kit (Black) now online and benefit from fast delivery.

www.overclockers.co.uk

...to provide a total of 96GB?

 

[itm]

What is your PC?

Very hard to give advice without knowing the CPU and motherboard

B450 AORUS ELITE / AMD Ryzen 7 2700X

 

[itm]

oh that's very unlikely.
zen/zen+ are/were notoriously finicky with ram
you'd be lucky to run 4 matching sticks of 8gb ram at anything higher than 3000mhz

So if there are currently 2 x 16GB sticks in place, and I want to upgrade it to either 64GB or 96GB, does that mean I should be looking at ditching the existing two sticks and completely replacing the RAM?

 

[itm]

The bigger question is what are you doing that you think needs 64 or 96GB of ram and is "ok" on a 2700X CPU?

I run a number of concurrent VM's using Virtualbox and am continually running out of RAM

 

[itm]

The best option then is to buy a 2x 32GB kit - you've nothing to lose by trying it with your existing RAM (although probably better to put the new kit in slots 1 & 2, and move your old RAM to slots 3 & 4).
Worst case it ends up being unstable and you remove your old RAM.

OK thanks. The existing RAM is in slots 2 & 4, presumably for a reason but I can't remember why. What's the reason for using slots 1&2 for the new RAM?

 

[itm]

According to the manual slots 1&2 are what should be used for Dual Channel (although 3&4 is also acceptable)

That's interesting...looking at that table I inferred that the columns DDR4_4 - DDR44_1 referred to the 4 RAM slots, and that to take advantage of dual channel you should use either slots 1&3 or slots 2 & 4.
Presumably I am misinterprering this table?

 

[itm]

The bit above the table is key - ChannelA = slot 2 and slot 4, Channel B = slot 1 and slot 3.

So you need to use a slot from both of those channels, i.e. slot 2 and slot 1, or slot 4 and slot 3 (which is what the diagram below shows, for 2 modules use either DDR4_2 and DDR4_1, or DDR4_4 and DDR4_3.

Sorry I'm still being really dumb...the text above the table says "Channel A: DDR4_2, DDR4_4".
In the table, DDR4_2 and DDR4_4 are the first two columns in the table. Do the 4 columns in the table not correspond to the 4 RAM slots on the motherboard?

 

[itm]

Yes but they aren't in order - hence why it has 2, 4, 3, 1 after the DDR4_

Ah OK gotcha - thanks for clarifying.

So do you think I'd see a noticeable increase in performance if I moved my existing RAM from slots 2-4 to slots 1-2?

 

[itm]

Agree with Armageus
Although you should note that high capacity RAM sticks also stress the IMC, so, you may find that even with 2 sticks of 32GB RAM, you may need to fiddle with voltages/speed/timings and there still may be a chance that it won't be 100% stable unless at JEDEC speeds (ie 2400mhz)

Is that something which is only likely to manifest itself under gaming-like conditions (as opposed to say productivity apps, audio production or music production)?