Welcome back PCWorld fans, Keith here. Today I’m going to break down graphics cards jargon
so that you can better understand graphics cards reviews. I’m as guilty as any other reviewer for
jumping right into extremely technical language in my GPU reviews, and I know if you’re new to
the DIY PC community or even someone looking to upgrade your pre-built machine, then a lot of
the language used by reviewers may go right over your head. So let’s get into those details.
First, let’s make sure we’re all on the same page about what a graphics card is. At its most basic,
a graphics card is an add-in board that has all the components necessary to generate 3D graphics
or other graphics accelerated functions like video playback and provide a display source
for the computer. Powering that output is the graphics processing unit,
or GPU, and currently 2 major companies—NVIDIA and AMD—produce them for both the first-party
and third-party graphics cards that you can buy. A third company, Intel, will enter the market in the
next 6 months or so. For now we’ll be using NVIDIA and AMD as references through this video.
As I just mentioned, at the heart of every graphics card
is the graphics processing unit, commonly referred to as the GPU. It’s where all the acceleration
for your GPU-dependent workloads takes place, whether that’s pumping out blazing fast frame
rates for your competitive gaming experience or speeding up your Adobe Premier edits.
And making it all work are the graphics cores, shader cores, and other additional silicon inside
that GPU. Let’s break down what those do. When looking into AMD’s Radeon or NVIDIA’s
GeForce graphics cards, you’re going to hear two different terms for graphics cores: Compute Units
and Streaming Multiprocessors. Radeon cards will refer to Compute Units while GeForce
cards will call them Streaming Multiprocessors or SMs. These sit grouped together on the GPU,
sharing die space with any additional silicon dedicated to specialized tasks, and they’re what
allow the graphics card’s performance to scale up and down because they’re built on blocks. In
reviews and marketing you’ll typically see the total number of these shader cores mentioned
more often than the CU or SM count. In general, the more compute units or SMs you have, the better
the performance. But I will stress that compute units and SMs shouldn’t be directly compared,
as their designs are different for each vendor. Inside each Compute Unit or Streaming
Multiprocessor are ‘shader cores,’ which again have a different name depending on the vendor.
AMD calls them Stream Processors while NVIDIA calls them CUDA Cores.
Generally speaking, they have similar goals of completing parallel processes as quickly
as possible for all GPU functions. But again, they aren’t directly comparable on sheer count,
so don’t buy a graphics card based on it having a higher stream processor or CUDA core count.
That’s a common mistake people make when deciding what to buy.
The speed at which these shader cores operate is known as the GPU frequency, and it’s typically
rated in megahertz. These days GPUs operate at very high frequencies, pushing 2000MHz and beyond
with ease. Some people get caught up in comparing the speeds when choosing a graphics card,
but honestly you can only compare frequencies within architectures and not much else. For
example, if you’re looking at AMD’s RDNA2 graphics cards, you have to stay within that GPU family
when considering frequencies. Any attempts to match up Streaming Multiprocessor and/or
Compute Unit counts and then also core frequency between different GPU families will not actually
tell you which is the most powerful option. If you’ve read any review, you’ve likely seen
the terms TMU and ROP listed. So what do they do? Well, TMUs, or Texture Mapping Units,
are basically what they sound like. They’re the part within the GPU that fills the scene
with the textures needed to keep it from looking like a huge wireframe arrangement.
Its speed is measured by the texture fill rate, so keep an eye out for that as well.
Obviously, the faster, the better. But what about ROPs? That’s the Raster
Output Unit and it handles the last little bit of rendering work that the GPU does as it puts the
image on the screen. There was a time when the TMUs and ROPs were symmetrical in their count,
but have since been able to run with different amounts and are no longer tied together
within the GPU architectures. Depending on a GPU’s architecture,
it may sometimes come with additional silicon beyond the normal parts we’ve just discussed,
like Asynchronous Compute Engines in AMD cards that accelerate Asynchronous Compute functions or
Tensor Cores in NVIDIAs RTX cards that accelerate Machine Learning capabilities. As time marches on,
we’re seeing more and more new additional silicon being introduced to graphics cards,
so certainly keep an eye out for that when looking over reviews.
The last thing I’ll mention related to the GPU is the concept of process nodes. Process nodes refer
back to the semiconductor fabrication process, and marketing departments love to bang their drums
about them. It’s for good reason, though—they do matter. Generally speaking, the lower the
number, the newer the technology. Newer process nodes typically bring efficiency gains that allow
for higher core frequencies or lower power requirements—or both, when there’s a jump to
an entirely new, lower-numbered tier, like when going from 14nm to 10nm. Be aware though that
each node is named for marketing purposes, and really aren’t 100% based on actual measurements.
Because of that, they’re not directly comparable between different companies, either. At the time
of this video, AMD Radeon uses a 7nm node manufactured by TSMC while NVIDIA GeForce
uses a custom 8nm node manufactured by Samsung. The GPU may be the biggest component of a graphics
card, but it certainly can’t stand alone, and that’s where a graphics card’s memory comes
into play. Typically, most video card memory, or VRAM as it’s more commonly referred to,
is of the GDDR variety, and these days the cards run GDDR6 on the Radeon side and either GDDR6
or GDDR6X on the GeForce side. There was a time we had the HBM or High Bandwidth type
of memory running on consumer-grade graphics cards, but that faster memory is now relegated
to the Server and Professional markets. Like the GPU, memory also has different
terms you should know—let’s dig in. GDDR stands for Graphics Double Data Rate,
and it differs from your typical DDR RAM that you’d put into your motherboard. Instead, this
type of memory is entirely designed for working with graphics cards. Currently we’re seeing GDDR6
memory running at a speed of 16Gbps, which is extremely fast and about twice the speed of GDDR5,
which ran at around 8Gbps. AMD uses GDDR6 on all of its RDNA2 cards, including the top-tier
RX 6900X. NVIDIA also uses GDDR6 on their Ampere-based cards for the RTX 3070 and lower,
but for the RTX 3070 Ti and up, it uses the faster GDDR6X, which operates between 19-21Gbps.
The speed of memory modules is only one piece of knowing how fast the memory system is
overall. Just as important is the memory’s “Bus Width”. This is how wide the memory interface
is between the GPU and the memory. The wider the bus and faster the memory, the greater
the bandwidth of memory flow. Think of the bus like a highway, the more lanes or wider it gets,
the more cars can move through at once. Even if they all go the same speed, you can get many
more cars down a stretch of 8 lane highway than you can on a 4 lane in the same amount of time,
and that’s kinda how bandwidth works. That bandwidth is the key to overall memory
performance. The higher the bandwidth, the faster data can be fed between the memory and the GPU
core. This metric is usually more important as you increase your monitor’s resolution
and have more pixels displayed in one scene. The bandwidth requirement to fill out a frame at
1080p is far less than that of a frame at 4K. But Keith, how do AMD’s RDNA2 GPUs hold their own
against NVIDIA’s Ampere GPUs with a much lower memory bus? Well, that’s due to the last level
cache, or a small pool of reserve storage that holds very commonly used memory instructions.
AMD calls this Infinity Cache. Basically, it functions as local storage for memory right on the
GPU die, so that the GPU doesn’t have to shuffle as much data to and from the actual VRAM. Pretty
neat stuff. How much you get depends on the GPU in question—for example, the RX 6600 XT has only has
32MB of Infinity Cache while the higher-tier RX 6800 has 128MB. It’s a big difference.
Naturally, you have to feed power to all of these components, and so I’m just going to
brush across the general terminology and what you should be on the lookout for.
TDP, sometimes known as TGP, is quite decisive when discussing computer components because every
vendor seems to use whatever metric is best for them. While TGP is the Total Graphics Power, the
TDP of a GPU is supposed to be the Thermal Design Power or maximum amount of heat generated by the
card under normal loads, and many people use it as shorthand for how much power draw and heat to
expect from a graphics card. But I would honestly say that on this one, don’t get too hung up on the
number. Rather, focus on what reviews say about actual power draw and the efficacy of the cooling
solution for the card you’re looking at. The components that handle power delivery are
important and will often be referred to as ‘power phases’, ‘chokes’, or ‘MOSFETs. They
act as transformers by taking the power from the Power Supply and stepping them down to the
proper voltage for the GPU and memory. The more of these that exist, the cleaner the step down can be
and that can allow for better power delivery to the GPU and keep it running
more consistent in its clock speed, so keep that in mind when researching a card.
A graphics card can pull all of the power it needs through the PCIe slot and not require any
additional juice, or it could require the use of multiple 6 or 8 pin PCIe power connectors.
Generally, the more powerful the GPU, the more likely you’ll need one or more power connectors.
Keep an eye out for how many a graphics card requires and make sure you have those connections
available on your power supply. Oh yeah, be aware that NVIDIA uses a proprietary 12-pin
microfit connector for its RTX 30 series Founders Editions cards—you’ll need to make sure to use
the included adapter or an alternative to make it work with your power supply.
Some people find the rear ports on a graphics card confusing, but it’s actually pretty
simple. Basically, this is where you plug in your monitors, TVs, or VR headsets. Usually you get a
combination of HDMI and DisplayPort connections, but we’ve also seen recent cards that make use of
USB Type-C connections—useful for monitors that can take advantage of that.
What you need to research about these ports is the version of HDMI or DisplayPort you get.
Each generation supports different resolutions and refresh rates. For example, HDMI 2.0b caps out at
4K 60Hz, while HDMI 2.1 can go up to 4K 120Hz. Well, that brings this explainer to a close.
I really hope by this point you’re armed with a bit more knowledge and understanding of what
reviews are talking about when these terms are thrown around. There’s more to learn for each one,
of course, and so if you want to know what’s IN a Streaming Multiprocessor
or a Compute Unit or other details along those lines, let us know in the comments below. If
you enjoyed this video and got something out of it, please hit that like button and make
sure you’re subscribed here at PCWorld for even more PC Hardware Explainers, Reviews, and News!