4. Will GPUs have direct access to DRAMs or CPU mediates in between???
Generally, the CPU is the only component that has direct physical access to the system memory. This was first introduced several years ago after the northbridge component or memory controller hub of a chipset became integrated in the CPU with the Athlon 64 and 1st Generation Intel Core i-series.
But with the Radeon 6000 series, AMD introduced a technology they're branding as Smart Access Memory, or SAM, otherwise known as Resizable Bar Support. This allows for a 'flyover' type access inside the CPU that allows the GPU to communicate directly with the system memory without any mediation by the CPU. It's pretty cool stuff.
3. Forgive my stupidity, Does CPU directly connects to gen 4 pcie NVMe port and the gen 4 gpu port for transmission of data, and not chipset involved as a mediator here?
For AMD, their processors are based on a 'system-on-a-chip' philosophy that was popularized with their AM1 platform. A lot of core components are integrated into the processor with SoC's. And with AM1 there wasn't even an actual chipset. It was just the processor and everything hanged off of that, from the bios to usb ports, to expansion slots to sata controllers.
With AM4, the chipset is no longer a core component that is absolutely essential to the system. It's more of an in-law that you visit every now and then to borrow power tools or cooking pots. The differences between X570, B550 and A520 is more for market segmentation, motherboard profitability and to play into the consumer mindset with established standards when it comes to platforms (that is there should be a high end chipset, a mainstream one and an entry level one). They offer features, but not raw performance upgrades. You could have an A520 motherboard with the VRM of an X570 and you'll see zero difference in CPU benchmarks.
So yes, with the current AMD chipsets, the CPU is directly interfacing to the graphics card, storage (nvme and sata), and USB ports. But the exact implementation varies from board to board. It's up to the manufacturers to decide what/how to connect to the CPU.
2. When we transfer data from a SATA SSD from Gen 3 NVMe port / a direct SATA Port(500MB/sec) to gen4 NVMe device, as it is obvious there will be a speed mismatch, will that be a Bottleneck or not??
Point to note, is that sata is always sata, it can never be anything else. When you insert a m.2 sata drive into the motherboard, it will be using the sata pins of that interface, the nvme/pcie portion of the interface is unused in that situation. The m.2 standard specifies usb, sata and pcie pins on the same tiny connector. There's no overlap, but motherboard manufacturers can choose to exclude any of the three, so you could have an m.2 slot with no usb or pcie, but just sata. Or just pcie but no sata or usb. In such implementations, nothing bad happens if you install an incompatible device, it's just not detected in the bios.
Since interconnects are asynchronous, the transfer speed would be limited by the sata drive. But this doesn't mean you'll have a bottleneck. You could copy from another sata drive at the same time to the same nvme and get 2x 500MB/sec speeds. Or three at 1500MB/s, theoretically. It'll increase for as long as bandwidth is available and the flash memory on the nvme drive can keep up.
Transfer speeds are like power ratings on a power supply. If a system only needs 50w, a 500w power supply can happily supply that, even though it is rated for more. If an nvme drive is rated at 5000MB/s then you can write to that from a 10x sata raid 0 array at 5000MB/s, again theoretically.
i have few more doubts! please clear it!
1. as u know B550 Offers 1 GEN 4 pcie port and another 1 GEN 3 PCIE Port for GPU, if i use multiple GPUs, not SLI or CROSSFIRE, 2 independent GPUs Connected in Gen 4 first port and another one in Gen 3 port, now i am gonna do a VT-d i/o with gen 3 GPU and will attach a completely different monitor, and will redirect a VM to that GPU, as the set up is like that.
Q1) will the Gen 3 operate on x16 or will it be x8 or x4 coz, the specs says the MOBO supports x4, does that mean it supports only x4 or will it operate on x16 lanes As it is an independent GPU .
Q2) or Whenever there is multiple GPUs accomodated in 2 different GEN Ports, will they only operate in x8 lane regardless of SLI and Crossfire.
There's a few things to unpack here. First is the concept of PCIe Lane Bifurcation. Every motherboard's manual will explain how PCIe lanes are distributed. Taking a generic example of a motherboard with 2 16x slots, when you have one GPU installed in the first slot, it'll have access to all 16 lanes. But if you install a GPU, or any other device in the second slot, then the lanes are automatically split into 8x for the first and 8x for the second slot. This is non-configurable, it happens automatically with most non-HEDT chipsets (anything that isn't x99, x299, x399 or trx40).
Now for B550, you'll have 4 lanes to the m.2 slot for storage, and 16x lanes for the first pcie slot, intended for the graphics card. Any other pcie device you install will be connected to the chipset, and will have to go through the gen3 link back to the CPU. It will have to share bandwidth with everything else attached to the chipset, so it is a sub optimal configuration. It will be bottlenecked in some way. This is how it would be for the vast majority of B550 motherboards.
But of course this depends on the motherboard's implementation. As an outlier example, the Asrock B550 Taichi has three pcie 16x slots, the first two are connected to the CPU and the last one is connected to the chipset. The first one is 16x electrically, but this will automatically drop down to 8x if a card is installed in the second slot. The second slot is 8x electrically. And the last one is 4x electrically. So if you install graphics cards in the first two slots, then they'll both be directly connected to the CPU at 8x gen4. And this is as good as it gets for dual graphics card systems that are not HEDT based.
To answer your question, the speed of the device is dictated by what's possible with the slot that you're going to be using. A top end gen4 graphics card with a 16x connector, if installed in a 4x gen3 slot, will only operate at 4x gen3 speeds. Keep in mind that any gen3 slot on a B550 motherboard is through the chipset, and never directly to the processor.
PCIe is designed to be backwards compatible/switchable.
As practical example, take a look at this riser cable. It's a 1x cable, and I cut off the edge, opening up the slot:
I'm using this cable to install a 16x graphics card into a 1x slot, and it works perfectly fine at 1x speeds because that's how PCIe is designed:
And if you look closely, the card has a 16x sized connector but the pins are only in the first half, this card is actually 8x electrically.
I apologize for the dust, I wasn't expecting visitors, haha.
