Monday, April 25th 2022
NVIDIA RTX 40-series "Ada" GPUs to Stick to PCI-Express Gen 4
NVIDIA's next-generation GeForce "Ada" graphics architecture may stick to PCI-Express 4.0 as its system bus interface, according to kopite7kimi, a reliable source with NVIDIA leaks. This is unlike Ada's sister-architecture for compute, "Hopper," which leverages PCI-Express 5.0 in its AIC form-factor cards, for its shared memory pools and other resource-sharing features similar to CXL. This would make Ada the second graphics architecture from NVIDIA to use PCIe Gen 4, after the current-gen "Ampere." The previous-gen "Turing" used PCIe Gen 3. PCI-Express 4.0 x16 offers 32 GB/s per-direction bandwidth, and NVIDIA has implemented the Resizable-BAR feature with "Ampere," which lets the system see the entire dedicated video memory as one addressable block, rather than through tiny 256 MB apertures.
Despite using PCI-Express 4.0 for its host interface, GeForce "Ada" graphics cards are expected to extensively use the ATX 3.0 spec 16-pin power connector that the company debuted with the RTX 3090 Ti, particularly with higher-end GPUs that have typical board power above 225 W. The 16-pin connector is being marketed as a "PCIe Gen 5" generation standard, particularly by PSU manufacturers cashing in on early-adopter demand. All eyes are now on AMD's RDNA3 graphics architecture, on whether it's first to market with PCI-Express Gen 5, the way RDNA (RX 5000 series) was with PCIe Gen 4. The decision to stick with PCIe Gen 4 is particularly interesting given that Microsoft DirectStorage may gain use in the coming years, something that is expected to strain the system bus for the GPU, as SSD I/O transfer-rates increase with M.2 PCIe Gen 5 SSDs.
Sources:
kopite7kimi (Twitter), VideoCardz
Despite using PCI-Express 4.0 for its host interface, GeForce "Ada" graphics cards are expected to extensively use the ATX 3.0 spec 16-pin power connector that the company debuted with the RTX 3090 Ti, particularly with higher-end GPUs that have typical board power above 225 W. The 16-pin connector is being marketed as a "PCIe Gen 5" generation standard, particularly by PSU manufacturers cashing in on early-adopter demand. All eyes are now on AMD's RDNA3 graphics architecture, on whether it's first to market with PCI-Express Gen 5, the way RDNA (RX 5000 series) was with PCIe Gen 4. The decision to stick with PCIe Gen 4 is particularly interesting given that Microsoft DirectStorage may gain use in the coming years, something that is expected to strain the system bus for the GPU, as SSD I/O transfer-rates increase with M.2 PCIe Gen 5 SSDs.
28 Comments on NVIDIA RTX 40-series "Ada" GPUs to Stick to PCI-Express Gen 4
Day180 PCI-E 5 device still= 0
Poor Intel
Earliest I predict it being a part of mainstream is 2025, weirdly Intel may push it because it's the new entrant & this could be a differentiating factor they'd obviously wanna promote!
I mean, PCIe 4.0 x16 will have the same bandwidth as PCIe 5.0 x8, meaning you need 2x PCIe 5.0 NVMe at full speed and on RAID 0 to really make things closer to a bottle neck.
But again, I wish it will have PCIe 5.0 just for the sake of it and coz other things will have it in it's lifetime.
I mean, you can certainly have a bus-powered card, (if you castrate the connection to x4, and the bus to 64-bit - 6400 or you take the 3060, then under-clock to 3050-performance)
If the rumours are true and the frequency of Navi 31 is 3GHz, then it will have logically double the pixel-fillrate of Navi 21 (Navi 33 64RBs half of Navi 21, Navi 32 128RBs, Navi 31 192RBs) while the memory bus will still be 256bit and with the GDDR6 being at 6950XT level or slightly more (20Gbps?, the Samsung 24Gbps option probably shouldn't be ready for launch) it will need to throw the kitchen sink in order not to be bandwidth limited, so at least 256MB infinity cache (rumour is for 512MB which is an insane amount of transistors/mm2 on 6nm, without the additional logic that the module will incorporate, we are talking for at least 24 billion transistors and more than 250mm² just for the 512MB cache portion of the chiplet) , PCI-E 5.0, better compression etc in order to help with all the memory access related issues of the memory stack.
Then there's the added overhead of getting two chiplets to talk to each other (all while sharing the same castrated 256-bit bus!) The only thing improved in this aspect is the doubling of infinity cache, plus a 10% bump in GDDR6 clock!
You'll be lucky if the performance is 40% faster at 4k
See TPUs review on this.
Now seriously, the easy prediction i can offer is that if infinity cache is 512MB, AMD will try to label Navi 31 as an 8K capable card, forcing reviewers to examine 8K resolution and will try to change the narrative into how it can win in some titles in 8K res vs Nvidia AD102 with it's only 96MB cache, when in reality the comparison should have been at 4K where the 96MB for the Nvidia Architecture is just fine...
www.techpowerup.com/review/pci-express-4-0-performance-scaling-radeon-rx-5700-xt/
The difference between PCIe 2.0, 3.0 and 4.0 were 1% or 2%, depending on the resolution.
The next year he followed up with a more testing, but this time with a 3080.
www.techpowerup.com/review/nvidia-geforce-rtx-3080-pci-express-scaling/
In this series of testing, he included PCIe1.1 spec in the 16x lanes as well as PCIe1.1 8x lanes. For PCIe 2.0 the difference where few percent more, but PCIe 3.0 and 4.0 were still at a 1% difference, not enough to be at all worried about.
While a 3090 or a 3090ti are faster than a 3080, they are not so much faster as to present serious PCIe bus bottlenecking situation for the PCIe 3.0 bus, and minimal bottlenecking for PCIe 2.0.
The problem is that there aren't many people having 8K displays (and those aren't OLED based unless we are talking about 10.000€-30.000€ TVs) and the forecast is that it will take around 5 years for 8K OLEDs to reach mainstream prices (when Chinese manufacturers gradually ramp up production in the next 5 years - let's see how the war and its reverberations will escalate first :(
And honestly I'm sick and tired every time AMD tries to change the narrative however they fit them (for example they decided for 6650XT, a $400-500 SRP card depending on the brand/model to place it as an 1080p card, guiding the reviewers to take priority in their conclusions for the 1080p difference vs the competition due to the fact that infinity cache size kills the performance at higher resolutions (for example a MSI RTX 3060 Gaming X is 1-2% faster than a MSI RX 6650XT Gaming X at 4K)
Sure 4K isn't the intended resolution for these cards, but there are many games like Doom Eternal, Resident Evil 3, F1 2020 etc + older ones of course that the MSI RTX 3060 Gaming X averaging more than 60fps at 4K max settings, now add to that all the games that with slightly lower settings can hit 60fps at 4K with very minor visual differences and the catalog isn't small.
But set aside the 4K argument which rightfully shouldn't be the main criteria for 3060-6650 performance difference, why not 1440p, is it too much to ask for a 400-500 SRP card? (after all the average fps in TPU setup, a 6650XT is hitting at QHD is very similar with a reference 6900XT at 4K, around 82 vs 87 average fps, so if 6900XT is fine for 4K why not QHD for 6650XT?) Is it the fact that $399 SRP 3060Ti is around 20% faster in QHD and +37% in 4K for example? (reference vs reference or OC vs OC)