Whether we're talking dollars in your bank account, items on a seafood buffet, or dates
you've got lined up on Tinder, more is generally considered to be better. A sentiment that also
seems to hold true with the number of cores in your computer's CPU. At least if you buy into the
marketing. But hold on. Even though having many cores definitely gives you a boost in multi-threaded
applications like rendering 3D animations, there are actually situations where more cores
gives no benefit whatsoever, or can even actually hurt your system's performance.
But how could this be? Well, to start off with, the more cores you pack onto a CPU,
the more power they need, and the more heat they generate. And remember that because CPU cores are
crammed into a relatively small space, manufacturers end up working against some serious limits
when it comes to thermal design power or TDP. This means that to prevent the CPU from drawing too
much power and producing too much heat, the individual cores have traditionally run their
clock frequencies lower to improve efficiency. And even if the advertised boost clock for a CPU
with lots and lots of cores can appear to be high, it's often the case that they cannot maintain
these clocks for long periods of time, or that they only do it when you're running very light
applications. So if you're using your computer mostly for applications where single-threaded
performance matters more, such as games, that super-expensive 18-core CPU might actually yield
you a worse experience than something cheaper. And if you go with a really high-core-count CPU,
there's another wrinkle with how processors with that many cores access the system memory.
You see, in some cases, these larger CPUs need to have their cores split into two groups or
nodes of cores, with each group getting its own memory controller and segment of the physical
memory in a scheme called non-uniform memory access or NUMA. This is generally quicker than
the opposite solution called uniform memory access or UMA, where all the cores share one
big pool of memory. But here's the thing, a CPU that uses NUMA, which is better for latency-sensitive
applications, can often struggle when running a single program that uses tons of threads.
Because of the different memory access times between the nodes and the fact that each node
would have to wait on the other one to finish working on the same data, highly multi-threaded
programs like these often don't want to cross nodes, even if it would mean being able to take
advantage of the entire CPU. So back to UMA then, right? No. Because one controller manages all the
memory accesses to give every program equal time, rather than allowing access to the memory more
directly as in NUMA, UMA has a built-in performance penalty that increases the more nodes your system
has to manage. So using a CPU with separate groups of cores means you're going to be subjected to
one of these drawbacks and you're going to take a performance hit either way. And these are problems
that you simply don't run into on smaller chips with fewer cores because you're not dealing with
multiple nodes. But getting away from memory access, sometimes the cores themselves are even
designed in a way that bottlenecks them the more of them you slap onto a chip. Do you remember
how before Ryzen AMD processors seemed to be significantly slower than Intel despite having
more cores? Well a big reason for this was that those old bulldozer FX processors didn't use
full cores. Instead an FX CPU advertised as having eight cores would in reality have eight
integer units but only four floating point units that were shared between the eight cores. So if
you don't know what a floating point unit is you can learn more about that right up here. But the point is you could think of these CPUs as having four half cores that were missing which severely
hampered their single threaded performance in some key applications. Now this design allowed AMD
processors to handle more threads for a cheaper price but it also meant that their real world
performance lagged way behind Intel and the only way AMD could try and compensate was to increase
clock speeds which increased heat output and contributed to AMD's reputation for hot running
CPUs for many years. So what's our bottom line then? Although both AMD and Intel are using much
wiser strategies for their many core CPUs and clever boosting techniques to give them similar
single threaded performance to their less costly brethren, if the best sales pitch for a super
premium product is that it doesn't suffer a performance penalty in the applications that you
use, well you'd better make sure you've got a use case for it before spending your hard-earned cash
and no playing Fortnite and watching Ted Quickie definitely don't count. So thanks for watching
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