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?

 

[Armageus]

It's certainly possible, but not always advisable

98% of the time it'll be fine, especially in your case the likelihood of it working is increased by them being from the same manufacturer, same speed, same timings etc.

The other 2% of the time it can be a case that no matter what you do (e.g. manually setting the timings because the XMP profiles are slightly different) you struggle to get them stable, or simply you have a CPU whose memory controller can't cope with running 4 sticks (or needs additional voltage to do it)

 

[tamzzy]

especially in your case the likelihood of it working is increased by them being from the same manufacturer, same speed, same timings etc.

yes but not quite, and especially with corsair because they do use different manufacturers/densities hence why they have the version numbers on the ram sticks
even crucial did this to their ram too when they moved to higher density chips...they kept the SKU the same, but there were only 4 chips compared to 8 - the primary timings were the same but the secondary/tertiary were vastly different and slower on the high density chips

 

[Tetras]

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?

What is your PC?

Very hard to give advice without knowing the CPU and motherboard.

 

[itm]

What is your PC?

Very hard to give advice without knowing the CPU and motherboard

B450 AORUS ELITE / AMD Ryzen 7 2700X

 

[tamzzy]

B450 AORUS ELITE / AMD Ryzen 7 2700X

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

 

[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?

 

[Armageus]

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?

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

 

[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

 

[Armageus]

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

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.

 

[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?

 

[Armageus]

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?

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

 

[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?

 

[Armageus]

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?

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.

 

[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?

 

[Armageus]

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?

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

 

[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?

 

[Armageus]

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?

Outside of synthetic benchmarks or the select few memory sensitive games then I doubt you'll be able to notice.

 

[tamzzy]

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?

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.

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)

 

[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)?