(dramatic music)
- Wait a second.
Everyone knows it's bad to mix and match your memory.
But how bad is it?
I mean, if you found a really sweet deal
to double up the RAM and your gaming rig,
would you be such an evil person if you pulled the trigger?
What if the RAM that's in your system
isn't available anymore?
Are you stuck with it forever?
Let's find out.
After we find out just how smoothly Linus here
is gonna segue to his sponsor.
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(upbeat music)
We never wanna feed you misinformation or myths,
particularly if it causes you to miss out
on a free or cheap upgrade.
So we took five different memory sets from our inventory,
rated for various speeds and latencies,
throw them on an AMD test bench
with a Ryzen 5 3600X and 2060 Super, and went to town,
checking configuration after configuration
after configuration after...
Well, you get the point.
And after many grueling hours of mind-numbing benchmarks,
we're here to give you the exciting results.
Guess what? It barely matters.
Or at least, it sometimes barely matters.
We created a baseline for reference
using two eight gig modules clocked at 3,200 megahertz
with primary timings of 6-18-18-36.
We ran our benchmarks, took notes,
and then started swapping out modules one by one.
And you might be as surprised as we were to find out that,
honestly, for the most part,
with two sticks you can get away with quite a lot
as long as you're willing to tweak some values
here and there in the system BIOS.
If you don't overclock your memory subsystem.
And I'm talking either with XMP or manually,
RAM compatibility with DDR4 has come a long way
to the point where basically it just freakin' works.
Faster modules will generally have no issues clocking down
and running steady with the slower ones,
especially if they're under four gigahertz.
And our performance measurements demonstrate this
with pretty much all of our configurations
within the run-to-run variants of our tests.
But the enthusiasts among you will know
that if you wanna get the most out of a modern system,
increasing your memory speed is really important.
What if we take then half of our reference kit
and half of a slower kit and run them in dual-channel
at the reference kit's frequency of 3,200 megahertz?
Our slow kit here is timed pretty similarly, 16-18-18-35.
But the traditional rule of thumb
is that for every speed bin bump,
you would expect to also raise your CAS latency by one.
I am really not sure if this is gonna work.
Crazily enough, though, the results look pretty good.
Almost as good as our RAM style Tech Scarf on LTTStore.com.
And the benchmarks look identical.
So what we've managed to show here is that if you get lucky
and you're mismatched RAM will run at your target speed,
there's unlikely to be any performance difference.
But remember how I promised we'd find some differences?
What happens if we up the ante,
and mix our 2,666 with our high-speed 4,000 megahertz kit?
Well, the reason DDR4 4,000 costs more than this stuff
is that it's been sorted or binned by the manufacturer
according to their internal performance targets.
Now, sometimes you get lucky
and this puppy'll over overclock to the moon,
but other times, you get our little friend, Mr. 2,666 here.
He managed to be compatible with the big, bad,
extreme gaming modules, but not at their rated speed,
where the system failed to even power on properly.
Things broke down even further
when we tried to populate more than two DIMM slots.
The thing is the more modules you install
the greater the load on your CPU's
integrated memory controller.
This didn't cause any performance issues per se,
as long as we could get the RAM all running,
but it did cause some flaky and undesirable behavior.
For example, when we populated three slots with a mixture
of our reference and slow modules,
the system would post and bench at 3,200 speeds just fine,
at the start, but here's the thing.
AMD's Ryzen processors have a feature called flex mode
that allows two modules to run in dual-channel,
with a third running in single-channel.
That's great for getting maximum performance
out of a non-ideal configuration,
but you've gotta be very careful
how you populate your slots.
As soon as we put our 2666 module in the B1 slot,
it got real unhappy, spitting out memory error codes
and getting stuck in a restart loop
until we reset the CMOS and dialed it all back to 2,666.
As for populating all four DIMM slots
and getting the system to work?
That was no easy feat,
with only a single configuration posting,
and only when we toned it all down to meet
at 3,200 megahertz.
That was below our highest rated modules
3,400 megahertz speed.
Funnily enough, though,
we tried back to this configuration later,
and despite using the same BIOS settings
with the same sticks in the same slots,
it actually failed to post properly during round two.
Which goes to show that while your friend
might have no trouble running a poop mix of memory
with no performance penalty,
you can't count on the same result.
And here's the big problem with that.
Two mixed modules was pretty much fine,
but most people aren't mixing memory
at the time that they buy their brand new system.
It's when they're upgrading down the line
and trying to max out an older system,
that these kinds of questions come up.
So the chance that mixing and matching
will result in unpredictability
when you're maxing out your system and filling all the slots
is just too high to ignore.
Speaking of unpredictable,
get subscribed so you don't miss the next installment
in our crazy Intel home upgrade series.
Andy is doing a man-cave. (clicking tongue)
Back to mixing memory though.
Is there anything that you can do to improve your odds?
Well, yeah, actually.
For starters, buying an upgrade
that is rated for the same speed and primary timings
will help your chances.
And so will finding a module that was built
using dies from the same manufacturer.
And when I say manufacturer, I'm not talking G.Skill
or Corsair or Kingston, I'm talking about the actual chips
that are soldered to the module.
So if you've got a module here with Samsung B-dies,
good for you, by the way, those are nice.
Try to get more of the same,
even if they have a different logo on the heat spreader.
"But, Linus," you might ask,
"what about different capacities?
"Can I pair up similarly specced
"eight gig and 16 gig modules
"and finally join team dual-channel?"
Yes, you can.
It's called asynchronous dual-channel.
So we also ran benchmarks with different capacity modules
of similar speeds and not only did it all register properly
but as long as your workload doesn't exceed the capacity
of the smallest module
you shouldn't notice any performance impact
With that said,
we still cannot in good conscience recommend going out,
buying whatever set of modules is on sale,
rubbing them together for good luck,
and throwing them at your rig.
Both the best and the worst thing about PC gaming
is that every system is wildly different from the next.
To the point where what works for your friend,
or for us today, might not work for you.
You might hit the silicon lottery
and get something that overclocks just fine
and has perfect compatibility,
or you might get something that runs
at exactly its rated speed and not a hertz more!
Worse yet, you might land yourself in a restart loop
or even run into unpredictable blue screens
on a rig that otherwise seems to be working fine.
So we would strongly recommend
if you're upgrading your memory
flip your current modules on Facebook Marketplace
or eBay or something and buy matching replacements.
If however, you've got the spare parts lying around
and you wanna see if you can give yourself an easy upgrade
with minimal or no performance loss,
and you're not afraid of a little bit
of fine-tuning in the event of some crashing,
the good news is that it can work.
So please do some of your own testing
and let us know in the comments below
just how far you were able to push your mismatched hardware.
Who knows, maybe you've had access
to a free upgrade this whole time.
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If you guys enjoy these kinds of deep dives into memory,
check out our previous look
at the performance impact of ECC memory.
It is slower,
but it might help you keep memory errors at bay.
You can check out findings on that sweet stuff
at the link down below
Or I think we've probably got a thing here. (clicks tongue)