- How can this
be faster than this,
when it should clearly be the other way around?
For years, I've been reading comments from people
who believe that the faster the gigahertz,
the faster the CPU.
And why shouldn't they believe that?
Gigahertz, also referred to as clock speed or frequency,
is quite literally a measure of how fast
the transistors in a processor switch.
So all else being equal,
more gigahertz should be more better.
But all else is not equal.
And in today's video,
we're going to dive into what those unequal things are,
and just how unequal they can be.
We're also going to dive into today's sponsor: Arozzi.
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To make sure that our test is as fair as possible,
both of our CPUs used identical test benches:
ASUS TUF B550-PLUS motherboards,
Noctua NH-D14 coolers,
16 gigs of dual-channel 3600 MHz C14 memory,
a Crucial P5 NVMe SSD,
and an RTX 3060 XC from EVGA.
We're going to have all these parts
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Well, most of them.
GPUs can be kind of hard to find.
(baby crying)
Now for the CPUs.
To keep politics out of the conversation,
we're going to be using only AMD branded processors,
but these principles can be applied to any other situation
where CPUs are being compared.
Naturally, we started with a full run of our benchmark suite
at out of the box speeds,
so we can see how the higher-gigahertz 3600XT
fared against the 5600X.
Remember that both of these CPUs
have exactly the same number of cores and threads.
Somewhat intuitively, the newer processor
does outperform the older one,
and sometimes by a considerable margin,
but why?
Well, many modern processors
are capable of dynamically boosting their clock speed
under favorable conditions.
Say, for example,
when they have a really good cooler installed.
Maybe our 5600X is just
a mad CPU frequency boosting machine.
Let's try reining it in,
and seeing what happens then.
At our locked clock speed of 3.4 GHz,
the 5600XT still wins in every single test.
So clearly then,
gigahertz is not the only determining factor
for CPU performance.
But these numbers aren't enough to tell the whole story.
Let's look at gaming.
If I only measured average FPS
in Shadow of the Tomb Raider and Grand Theft Auto V,
I might think that a 5600X is only about 5% faster
than a 3600XT in the real world.
But take something more CPU-bound like CS:GO,
and these two CPUs,
with the same core counts running at the same frequencies,
are nowhere near each other.
But then, dropping the clock frequency even further,
to 2.4 GHz,
it's clear that the lower the clock goes,
the slower our CPUs get.
So what is it?
Does gigahertz matter, or not?
There are a couple of takeaways here.
Starting with that, yes, gigahertz absolutely matters.
Which raises the question, then:
Why don't CPU manufacturers just run their chips
at higher clock speeds?
I mean, bring on the 10 GHz CPUs, am I right?
Well, that was the plan actually,
but higher clock speeds come at the cost
of more power consumption,
which tends to result in hotter-running chips.
Thankfully though,
there are a lot of other levers that CPU designers can pull
to improve performance,
which leads us to our second takeaway.
CPUs, or any kind of processor for that matter --
GPUs, phone SoCs, anything --
should never be compared using gigahertz alone.
It is clearly an important spec,
and manufacturers do need to disclose it
because it enables us to compare products
within their own families.
But if you want to talk about an M1 Mac
versus an Intel Mac,
or an AMD GPU versus an NVIDIA one,
don't even bring it up.
You would only be revealing your ignorance on the subject.
Let's talk then about some of the ways
a CPU can differ, aside from gigahertz.
An obvious one is that they can be designed
to process more threads or tasks in parallel.
Intel was the first to process two concurrent threads
on a consumer chip with hyperthreading, or SMT,
while AMD was the first to build a truly multi-core CPU,
with their X2 series dual-cores
that were capable of doing nearly double the work
under ideal conditions.
The only drawback to additional cores
is that they increase die size,
meaning cost and power consumption,
and they can't be used to accelerate
single-threaded workloads.
So in many consumer applications like games,
they're only helpful up to a point.
Currently AMD and Intel's mainstream lineups
top out at 16 and eight cores, respectively.
So we can't keep pushing core counts forever
and expect consumer applications to scale.
And clock speeds have been locked in the same range
for over 15 years.
Then, what have they changed
to really push forward single-core performance?
The simple answer is IPC, or instructions per clock.
If we think of a CPU like a mine,
and each core like a miner
running back and forth doing work,
the clock speed is how many times
our miner can run back and forth per second,
while the IPC is how much they can carry on each load.
Look at the Apple M1, for example.
Joe Average gamer might laugh
at its meager 3.2 GHz clock speed.
But when it comes to the real world,
it performs pretty damn well,
like this sexy retro GPU T-shirt from lttstore.com.
What that tells us about it
is that it has better IPC
than a CPU that runs at a higher frequency,
but performs the same.
The problem, though, is IPC sounds a lot simpler than it is.
You can't just add more instructions to each clock cycle.
Let's go back to our mine analogy.
The problem is that our mine contains
every single possible type of mineral or rock.
And let's say those represent different apps or programs,
and each of them requires specialized equipment.
So let's say you level up your miner
by adding more points to their shovel,
and suddenly there's a boost to your coal gathering.
But sifting for gold,
well the shovel doesn't help you with that,
so performance is entirely unaffected.
That's how you can see a new generation of CPU come out
that absolutely crushes Cinebench,
but gets the same FPS in games.
So IPC is problematic.
Along with clock speeds and core counts,
it's one of the most important ways
to predict a processor's performance.
And yet, unlike those other attributes,
nobody can agree on a fair and objective way to measure it.
The way that we enthusiasts use the term,
saying things like: this new CPU
has 20% higher IPC than the old one,
can be misleading.
A manufacturer could easily spend all their time
tuning performance for a single commonly-benchmarked program
like Geekbench or Cinebench,
when that wouldn't be representative
of the real-world experience of using it.
Though AMD and Intel
also throw the term around in this way when it suits them.
So, I blame them.
Now, there are major CPU design factors
that can cripple the real-world performance
of a "high IPC" CPU that's tuned for a particular benchmark.
Let's talk about waste.
Going back to our mine analogy,
adding cache to a CPU
is kind of like making easy piles of our minerals, or data,
that can be shoveled
and carted out of the mine more quickly.
The bigger the pile, the more likely it is
that you can just fill up your wheelbarrow, and off you go.
On the other hand, if there's nothing in the pile,
the miner has to go deeper into the mine,
or to the system memory, to retrieve it.
That's going to take longer.
Then there's the branch predictor.
It is kind of like mine supervisors,
who attempt to proactively communicate
which minerals are going to be needed in the near future,
rather than just having the miners wait around for an order.
CPU designers can dramatically improve performance
with accurate branch prediction,
but the logic for it takes up space on the CPU
that could also just be used to add more miners.
So it ends up being a delicate balancing act.
Speaking of the physical layout of the cores,
imagine if our miner parked their wheelbarrow
right next to the mineral heap
instead of five steps away,
and carried it like that.
CPU designers are always looking for ways
to make each load more efficient.
And sometimes the actual physical proximity of CPU elements
can be a big difference maker.
So an obvious solution to this problem, then,
is to stop using gigahertz,
stop using IPC,
and rather use a broad industry standard set
of real world tests.
The problem with that is,
if we're looking at real-world benchmarks,
we end up with real-world messiness,
including politics between competing brands,
who would each, naturally, prefer tests
that favor their own products.
This is why to this day, we still need reviewers,
lots of them,
so that you can see a wide variety
of different methodologies and test suites,
and how the product that you're considering stacks up.
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As always, thanks for listening, folks.
I hope it helps you make the right choice
next time you're looking to upgrade.
If you enjoyed this video, hey,
give a thumbs up and make sure to check out
"Is four-core still enough?".
You might be surprised by the results.
They're only helpful-
(sound of hitting the floor)