[SOLVED] why B550 mobos are limited to single CPU graphics PCI-Express 4.0 slot?

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Jan 22, 2021
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Hello All,

Discrete graphics card is mandatory for RYZEN 5 3600 CPU, majority of B550 boards are equipped with single PCI-E 4.0 with 16x speed (Directly connected to CPU) slot.
Boards do have secondary PCI-E 4.0 slot but runs only on 4x speed (connected to chipset).
MSI B550 UNIFY and UNIFY-X also don't have PCI-E 4.0 - 8x slot
I observed that only ASUS B550 strix-E gaming or Asrock B550 taichi or gigabyte B550 Vision D have secondary 8x slot but I feel those are too overkill to run Ryzen 3600
I saw multiple reviews of X570 Tomahawk but nobody complaint about single CPU graphics slot
What to do if primary PCI-E 4.0 slot gone dead ? should we put graphics card in PCI -E 4.0 with 4x slot or it never get dead unless physically broken ?
not every user looks for SLI but extra 8x slot would give ability to add graphics card if primary 16x fails
Just trying to understand logic behind keeping only single CPU graphics slot? Am I missing something...or miss understood
Any insights would be greatly appreciated

Thanks
Mahesh
 

DSzymborski

Polypheme
Moderator
That's an easy one: because price competition is fierce, so leaving out something that very few people will value gives you the space to offer the things that people will. Multi-GPU solutions are deader than the VCR at this point and PCIE slot failures are fairly uncommon (and people will be covered by warranty for years). "PCIE redundancy four years from now" is a very niche need.
 

DSzymborski

Polypheme
Moderator
That's an easy one: because price competition is fierce, so leaving out something that very few people will value gives you the space to offer the things that people will. Multi-GPU solutions are deader than the VCR at this point and PCIE slot failures are fairly uncommon (and people will be covered by warranty for years). "PCIE redundancy four years from now" is a very niche need.
 
Jan 22, 2021
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Thanks all for quick and valuable response.
Yes during the warranty period, we can get Mobo replaced if PCI slot dies. Most probably I assume that graphics card would die within 2 to 3 years and needs replacement . However After 3 years, once warranty period is over, ONLY CPU graphics PCI slot goes dead, we don't have privilege to use 2nd 8x slot to keep going, we are forced to use 4x slot or simply need new mother board or need to do paid repair

just one question:
How graphics card works with 4x secondary slot?
This is specially would be the case for high end gigabyte B550 arous master or MSI B550 Unify and Unify-x. These boards having 16 phase VRM with rich future sets but excluded 2nd 8x slot. One like me would expect to run these boards for 5 years even if primary slot goes dead.

Almost 10 years back I own M2N sli-deluxe board with single graphics card and after 3.5 years its primary graphics slot got dead somehow but it got life due to secondary 8x slot for next two years with same graphics card.

Many Thanks
Mahesh
 

DSzymborski

Polypheme
Moderator
Thanks all for quick and valuable response.
Yes during the warranty period, we can get Mobo replaced if PCI slot dies. Most probably I assume that graphics card would die within 2 to 3 years and needs replacement . However After 3 years, once warranty period is over, ONLY CPU graphics PCI slot goes dead, we don't have privilege to use 2nd 8x slot to keep going, we are forced to use 4x slot or simply need new motherboard or need to do paid repair

just one question:
How graphics card works with 4x secondary slot?
This is specially would be the case for high end gigabyte B550 arous master or MSI B550 Unify and Unify-x. These boards having 16 phase VRM with rich future sets but excluded 2nd 8x slot. One like me would expect to run these boards for 5 years even if primary slot goes dead.

Almost 10 years back I own M2N sli-deluxe board with single graphics card and after 3.5 years its primary graphics slot got dead somehow but it got life due to secondary 8x slot for next two years with same graphics card.

Many Thanks
Mahesh
Nobody's saying that it doesn't happen, or isn't useful. That's a strawman argument. It's just not a priority for consumers and thus, when hard decisions are made as to what features to have, the ones people are less interested in are cut.

Let's flip this around. What features would you sacrifice from these motherboards to get a second x8 PCIE slot? Because you have to sacrifice something.

A full-size tire is undoubtedly more useful than a doughnut when you have a flat tire. But almost every consumer car does not have a full-size tire. Why? Because car buyers would rather use the additional space a full-size tire takes up in another way than have a full-size tire. Consumers prefer the storage space or having a smaller car overall. You really only see full-size tires on cars that have more utility; the calculus of costs vs. benefits changes for that part of the market.

For the few people that must have it all, well, having it all costs more than having most of it.
 
Jan 22, 2021
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Thanks for response. Ultimately in the case of B550, really don't have to sacrifices anything if they do provide another 8x slot.
16 lanes are reserved for CPU graphics, it does not matter if you use it with single 16x or dual 8x
ultimately 2nd 8x slot if used, makes primary slot bandwidth also 8x by force but that is how multi GPU slots works since PCI-E 2.0. They may drop SLI support to avoid license fee if wanted to.
And graphics card operates with 8x speed maximum.

In fact they have only 4 lanes reserved for 4th gen M2 storage drectly connected to CPU and it does not affected by having 8x slot.

Rest of M2 slots are driven by B550 chipset no matter you have 8x slot or not.
The Sata port and number of M2 slots combination are the once where you need to make compromise / trade off but that is all about chipset lanes and not related to 8x slot.

In fact if there is 8x secondary slot direct from CPU, one can put add in card with bunch of M2 slots and attach more high speed M2 disks with 4th gen connectivity if wanted to. ASUS seems more mature than other Mobo manufacturers and maintained secondary 8x slot plus add-ins card with bunch of 4th gen M2 slots with their new B550 strix-E and XE boards. This action made there B550 offering fully compatible with x570 but with bit higher price point.

Its disappointing to see that MSI and gigabyte has dropped 8x support for secondary PCI-E slot for no reason despite having strongest VRM setup on their high end models and thus decreasing high end Mobo value

Thanks. I honor your 1st comment and agreed with fact you said. They are manufacturing Mobos with specs having current selling points. I got answer now.

I have posted question to identify if there is technical challenge or superseded feature in avoiding 8x secondary graphics slot but it seems there are no issues to include 8x slot on mid range to high end boards and without that it would be single point of failure for board graphics specifically for Ryzen CPUs considering long life of mother board. Although you can get replacement in warranty period, that's different story.

Thanks
Mahesh
 
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