So many of us only ever end up using one slot on our motherboard, usually for a GPU.
But what would happen if you filled all of them?
It's not that unrealistic. Let's say you're a gamer.
You gotta have your GPU, but you also need to connect your desktop to Wi-Fi,
so you throw in a wireless card. You stream, so you need to capture card, and you've got a pretty big game library,
so you're out of M.2 slots, so you add some more storage with one of these babies.
Then there's the fact that you've got this unnatural attraction to PCs with
lots of USB ports, so you throw in one of these, and that's five cards,
which happens to be the same or more than most modern motherboards can accept.
Will this overload your system in some way?
Well, as is the case with so many things in PC land,
the answer depends on what kind of CPU and motherboard you have,
what cards you're using, and exactly what it is you're trying to do.
Further complicating matters is that even PCI Express slots that look identical
can operate at very different speeds.
Let's break it down. Some slots connect directly to your CPU,
while others connect to your motherboard's chipset.
The CPU direct ones are generally going to provide the smoothest experience,
since they're not going to be shared with any other devices.
The issue is that the PCIe lanes, the data paths that feed these slots,
add a lot of cost and complexity to the CPU.
That's where chipset lanes come in. In PC terms, the chipset is a chip, or well, set of them, if you will,
that lives on your motherboard and handles a great deal of your computer's input and
output, or IO. SATA ports, USB ports, and network ports are commonly connected to the chipset,
and on modern platforms, that requires a lot of PCIe lanes.
Intel's Z790 chipset, for example, supports up to 28 additional PCIe lanes.
But this presents a problem. The problem is that the chipset itself has to have some kind of link to your CPU,
and this link usually takes the form of, you guessed it, PCIe lanes.
Now, as you can imagine, there wouldn't be much cost savings if this link
had the same number of lanes as the downstream chipset,
so typical desktop systems cut that link all the way down to just eight or even four lanes.
Now, in most cases, that's not a huge deal, and to illustrate why,
let's think of our system kind of like a restaurant. The CPU can be the kitchen, and the connected devices can be our customers.
Our GPU is going to sit at the 16-seater VIP table over here.
Every guest gets a dedicated chef, so no one ever goes hungry,
and the same goes for the four-seater family and friends table where our boot SSD hangs out.
As for the rest of the dining room, well, hey, as long as their orders are staggered,
nobody ends up waiting too long for their meal, and in the real world, that's usually how things go down.
Expansion cards like Wi-Fi, Sound, or USB and SATA cards,
even capture cards, are very unlikely to all be operating at peak capacity at the same time.
And even if they did, they wouldn't come close to saturating that link back to your CPU
because of their relatively low data rates.
However, where you can run into problems is if you're using your chipset lanes for high-speed
storage. Let's say, for example, you work with large amounts of high-resolution video footage.
You could overwhelm the link between the chipset and the CPU in multiple ways.
For example, by transferring footage from an external drive that uses the fastest versions of
USB or Thunderbolt to a high-speed PCIe drive that's also running off the chipset.
This could result in lower than expected speeds and even slow down
anything else that is connected to the chipset. Imagine, for instance, a capture card that starts dropping frames whenever you do a file transfer.
Another thing to watch out for, especially you gamers, is that many CPUs allow the 16-lane GPU slot to be split into two 8-lane slots.
This is good because it gives users the flexibility to install
two GPUs for machine learning or a GPU and another high-performance accelerator.
But it comes at the cost of reducing the bandwidth to your main GPU.
Making matters worse, the way the lanes are split up is not always easy to control.
You might consult your motherboard manual, good idea by the way,
and think, oh, okay, these two slots can share 16 lanes,
but I only really need one lane for this Wi-Fi card.
That leaves 15 lanes for my GPU.
But it doesn't work like that. The mere act of installing another card,
any card in that slot will more than likely cut your GPU bandwidth in half.
Fortunately, your gaming performance won't drop that much,
but there are cases where these fine details can make a big difference.
This high-speed network card, for example, uses 16 lanes that run at Gen 4 speeds.
If we put it into a Gen 3 motherboard, that's okay, it'll work,
but it will run at half the bandwidth. But then, if the slot on that motherboard were to only get 8 lanes,
now we've cut the overall bandwidth in half again to just one quarter of what the card expected.
Don't get too freaked out, though. You don't have a network card like that at home,
and unless you're moving around large amounts of data regularly,
you likely won't notice slowdowns just from having all of your slots filled.
If you do need more lanes though, the good news is there are solutions.
Workstation and enterprise platforms like AMD's Threadripper and Epic
or Intel Xeon are built with a huge number of PCIe lanes connected directly to the CPU.
The only problem is that if you need one of those, you're gonna have to figure out how to get one of your kidneys out as painlessly as possible.
Thanks for watching! If you guys liked this video, check out our other video on PCI Express Gen 7.