The PCI-E lanes from the CPU are not split, and are dedicated to the first PCI-E x16 slot. Most motherboards don't, including the Z77 Pro3: Motherboards optimised for multi-gpu setups can split the CPU PCI-E lanes to allow two slots to operate at x8 speed.
The last sentence/part is not normal for a standard dual GPU setup, instead the two slots fall back to x8 speed at PCI-E 3.0 serviced by the CPU. A good example would be a graphics card in the second PCI-E x16 slot.
It seems less of a worry unless you have other add-in cards using a lot of this bandwidth.Ī single PCI-E 2.0 x 4 card could saturate the DMI.
Pcie x4 usb 3 card full#
The DMI 2.0 interface is equivalent to 4 x PCI-E 2.0 lanes, so 2GB/s full duplex. I didn't realise each PCI-E lane was actually made up of two signalling paths for full duplex transfer. Even if you use 500MB/s each way, you still have 1.5GB/s to spare.ĭMI becomes a potentially significant bottleneck only for NVMe and SSD arrays but not many home users are going to copy massive amounts of data from NVMe to a RAID array of SSDs at 2GB/s while doing other stuff on some other drives. There is no problem there if all you have is individual USB3 and SATA3 drives: the DMI bus is symmetrical, which makes it 2GB/s in + 2GB/s out. The total bandwidth of the DMI is 2GB/s for this board (DMI 2.0). If you want to copy data from one drive to another, this needs to pass through the DMI into RAM, and then back through the DMI to the second drive. USB3 provides a dedicated RX and TX pairs, two in each direction for USB3.1 on Type-C, which eliminates the need to share bandwidth on a single wire pair and waste so much time waiting or polling. To that, you need to subtract USB2 protocol overhead, the protocol overhead of whatever device protocols are laid on top of it, and the fact that USB2 is half-duplex - whenever the host is sending commands or data to a device, the device cannot send anything back and devices need to wait for the host to poll them to declare interrupts, which means USB1/2 waste tons of time waiting to get polled by the host and switching between receive and transmit since USB1/2 only have a single pair to both receive data from and send data with.ĭue to all of the wasted time and overhead, you will rarely manage to extract more than 35MB/s out of USB2. There's very little performance difference if any at all.Ħ0MB/s is the raw theoretical absolute maximum data rate on USB2. Conversely you can buy a simple Rosewill add in card, power it from the PSU and split chores between your built in USB ports and the add in card. It's expensive but they do work to solve issues like that. And I'd consider that typical when someone can buy a dock for 40 dollars with that card I mentioned had four individual HUBS, one port for each hub, plugging devices into them won't cause amperage drops or performance drops on the other HUBS/ports on the card.
So not only does it come close, it matches it. So yeah it can match the native SATA throughput since the drive itself is the bottleneck. UASP further decreases the latency penalty of USB 3. I have a USB 3 dock here on my desk that will max out an OCZ enterprise SATA SSD, specifically an Intrepid 3700, I have multiple sizes. The USB controller used in a typical Western Digital or Seagate external drive enclosure is not going to come close to an internal SATA drive. I've never seen UASP devices, but I'm guessing you will only find this is in devices targeted at the server market. The USB controller does add latency and reduce performance compared to the native SATA interface of the drive. Never the less, I've never seen an external USB 3 drive match a SATA drive for performance. Sorry, USB 2.0 is up to 480 Mbps, or 60 MB/s although I'm not sure this is accounting for encoding overhead. I've attached backup disks to USB 3 that max the drive (150 - 200 MB/s depending on where the heads are) in exactly the same fashion as a native SATA. A 100MB/s hard disk would be consider slow by new drive standards. WIth USB 3 external enclosures supporting UASP drives easily max out. Modern SATA drives are capable of over 100 MB/s.Įverything stated here regarding performance of USB 3 and SATA attached USB is wrong. USB 3.0 is technically capable of 60 MB/s, but I've never seen more than 40 MB/s and the latency is relatively high. If you actually want any level of performance or reliability from the drive though, you would be better with SATA drives.Įxternal USB drives use SATA internally, but the USB controller adds another layer that reduces performance. Speed and power from an add-in card should be much the same as the onboard USB 3.0 ports.
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