Does a PCIe 3.0 CPU Limit Other Things???

[PC HEROES]

 

Hello... I have wondered for years now that if I or someone else got a PC like this: Example PC

 

Will the CPU which is locked on PCIe 3.0 take away from other Parts that are PCIe 4.0 like the Motherboard, M.2, and GPU? If the Motherboard has PCIe 4.0 Capability like being able to use a Gen4 M.2 and PCIe 4.0 GPU will it be Locked to PCIe 3.0 because of the CPU???

 

[filpo]

4 minutes ago, PC HEROES said:

will it be Locked to PCIe 3.0 because of the CPU???

yes, the CPU doesn't have the PCIe 4.0 lanes for these

AMD Ryzen 5 4600G Specs | TechPowerUp CPU Database

The chipset may split some of these lanes for extra M.2's etc. but they will still be at pcie 3.0 since the CPU doesn't have any PCIe 4.0 lanes

4 minutes ago, PC HEROES said:

Hello... I have wondered for years now that if I or someone else got a PC like this: Example PC

Are you considering this pc for you/a friend/a client?

Edited April 23 by filpo

[PC HEROES]

7 minutes ago, filpo said:

yes, the CPU doesn't have the PCIe 4.0 lanes for these

AMD Ryzen 5 4600G Specs | TechPowerUp CPU Database

The chipset may split some of these lanes for extra M.2's etc. but they will still be at pcie 3.0 since the CPU doesn't have any PCIe 4.0 lanes

Are you considering this pc for you/a friend/a client?

No, I was just using this as an example question. I would never pair a CPU that is Locked w/ PCIe 3.0 and use PCIe 4.0 Parts. Seems sad that just because the CPU is limited that the other should be too, like they somehow could not have found a way around this.

 

Also anyone else seeing this might get some knowledge out of it.

[filpo]

2 minutes ago, PC HEROES said:

Seems sad that just because the CPU is limited that the other should be too

it has to use the CPU's pcie lanes for the fastest bandwidth between m.2's/expansion slots so if the CPU's pcie lanes are at 3.0, that's the highest that can be used

3 minutes ago, PC HEROES said:

like they somehow could not have found a way around this.

PCIe compatibility is already quite good, like you can basically use any pcie gen with any other pcie device. Yes, performance will most likely be worse by some margin, but it will still most likely work

 

Put it like this, you can't make new lanes in a bios update, they're part of the CPU's hardware

3 minutes ago, PC HEROES said:

Also anyone else seeing this might get some knowledge out of it.

fair point 

[Bigchungusbutbigger]

You can't utilize the full speed of gen 4 ssds and newer GPUs are gen 4 So yeah thought for gaming, it's alright.

[PDifolco]

15 minutes ago, PC HEROES said:

 

Hello... I have wondered for years now that if I or someone else got a PC like this: Example PC

 

Will the CPU which is locked on PCIe 3.0 take away from other Parts that are PCIe 4.0 like the Motherboard, M.2, and GPU? If the Motherboard has PCIe 4.0 Capability like being able to use a Gen4 M.2 and PCIe 4.0 GPU will it be Locked to PCIe 3.0 because of the CPU???

 

The example PC is just bad unless it's the result of a GPU upgrade, but anyway it will be limited to PCie3 due to the CPU

This won't really affect anything unless you got a 4 lanes GPU like a 6400X,  your M2 speeds will be capped to 3GB/sec too, but it's not a big deal neither

[Agall]

26 minutes ago, PC HEROES said:

 

Hello... I have wondered for years now that if I or someone else got a PC like this: Example PC

 

Will the CPU which is locked on PCIe 3.0 take away from other Parts that are PCIe 4.0 like the Motherboard, M.2, and GPU? If the Motherboard has PCIe 4.0 Capability like being able to use a Gen4 M.2 and PCIe 4.0 GPU will it be Locked to PCIe 3.0 because of the CPU???

 

4600G and the APU dies are completely different, they're technically not 'Ryzen' architecture since they're using a monolithic die and not MCM. They'll usually have the same CPU performance capabilities, like any Zen3 8c/16t APU at the same clock will generally perform the same as a Ryzen Zen3 8c/16t CPU at the same clock, though the performance isn't 1:1 overall. The monolithic APU dies only have 16MB of L3 cache compared to Ryzen MCM CCDs that have 32MB for Zen2 or higher. Even the brand new 8700G only has 16MB of L3 cache.

 

The difference between the APU dies and Ryzen MCM dies also translates to their North Bridge (I/O die for MCM). They at least upgraded the North Bridge for the 8000G series to PCIe 4.0, but that's an AM5 part.

 

Really for anyone with that system, a drop in 5000x3D CPU would be amazing. Not only would it improve PCIe performance, but also fully utilize the RX 6650 XT since that's a PCIe 4.0 8x card. Even the 5600x3D if the system user lives nearby a Microcenter.

 

*Just make sure they're using a compatible BIOS before upgrading CPUs*

[Alex Atkin UK]

57 minutes ago, PC HEROES said:

Seems sad that just because the CPU is limited that the other should be too, like they somehow could not have found a way around this.

I feel you're missing the point here.  Those PCIe 4 slots are wired directly to the CPU, its the fastest connection to the CPU so the "way around it" is get a CPU with PCIe 4.

 

Let's say instead of wiring the PCIe x16 slot directly to the CPU they added a PCIe 4 MUX instead.  Sure, a GPU using PCIe 4 x8 would have the full bandwidth of PCIe 3 x16 (thanks to the mux doing the conversion to the CPU), but then that slot wouldn't be able to support native PCIe 4 directly to the CPU on a supported CPU, it would most likely be limited to PCIe 3 x16.  It would also add cost, complexity and more latency to that slot.  In 99% of cases, it would be a worse solution.

[PC HEROES]

17 minutes ago, Alex Atkin UK said:

I feel you're missing the point here.  Those PCIe 4 slots are wired directly to the CPU, its the fastest connection to the CPU so the "way around it" is get a CPU with PCIe 4.

 

Let's say instead of wiring the PCIe x16 slot directly to the CPU they added a PCIe 4 MUX instead.  Sure, a GPU using PCIe 4 x8 would have the full bandwidth of PCIe 3 x16 (thanks to the mux doing the conversion to the CPU), but then that slot wouldn't be able to support native PCIe 4 directly to the CPU on a supported CPU, it would most likely be limited to PCIe 3 x16.  It would also add cost, complexity and more latency to that slot.  In 99% of cases, it would be a worse solution.

I know that putting in a CPU that already has PCIe 4.0 is the "Preferred" thing to do. This was just a question and NOT a Real World Scenario. I know EXACTLY what I am doing. I posted this for people who might not know the differences between the two.

[Needfuldoer]

[ Moved to CPUs, Motherboards, and Memory ]

 

Computer components will only run as fast as the slowest link in the chain. If your CPU supports PCIe Gen3, but the motherboard and GPU support PCIe Gen4, then everything will run at PCIe Gen3 speeds because the CPU can't go any faster.

 

Every new generation of PCI Express doubles the amount of data each lane can carry. PCIe has very good forward and backward compatibility, so even if something isn't running at its full capabilities, it will run.

 

Source: https://en.wikipedia.org/wiki/PCI_Express#Comparison_table

 

The place where this really hurts for now is on PCIe Gen4 x8 video cards. In theory, they have as much bandwidth as a PCIe Gen3 x16 card. However, if you pair them with a CPU that only supports Gen3, they're only getting half the bandwidth they "should" have because there are only 8 lanes.

[PC HEROES]

25 minutes ago, Needfuldoer said:

[ Moved to CPUs, Motherboards, and Memory ]

 

Computer components will only run as fast as the slowest link in the chain. If your CPU supports PCIe Gen3, but the motherboard and GPU support PCIe Gen4, then everything will run at PCIe Gen3 speeds because the CPU can't go any faster.

 

Every new generation of PCI Express doubles the amount of data each lane can carry. PCIe has very good forward and backward compatibility, so even if something isn't running at its full capabilities, it will run.

 

Source: https://en.wikipedia.org/wiki/PCI_Express#Comparison_table

 

The place where this really hurts for now is on PCIe Gen4 x8 video cards. In theory, they have as much bandwidth as a PCIe Gen3 x16 card. However, if you pair them with a CPU that only supports Gen3, they're only getting half the bandwidth they "should" have because there are only 8 lanes.

Again... I don't need any Pics or Graphs explaining the differences between the different CPUs and PCIe Types. This was only supposed to be for people who DON'T know the difference but it is good to have them for those people. This Thread only needed a Yes or No Answer.

[Needfuldoer]

5 minutes ago, PC HEROES said:

Again... I don't need any Pics or Graphs explaining the differences between the different CPUs and PCIe Types. This was only supposed to be for people who DON'T know the difference but it is good to have them for those people. This Thread only needed a Yes or No Answer.

There is no direct yes or no answer to your question unless you ignore workload as a variable.

 

If you're just browsing or word processing, you won't notice a bottleneck at all.

 

If you're trying to play Cyberpunk on maximum settings at PCIe Gen3 x8, you might.