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USB 3 PCI-E card

Aggravated Salmon
By Aggravated Salmon
in Peripherals
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Go to solution Solved by mariushm,

Most if not all usb 3 controllers are designed to use a single pci-e lane ... so you'll have either 500 MB/s or ~ 970 MB/s theoretical connection to the chipset / cpu. However, due to arranging data in packets, you'll probably have 5-10% less of that. 

At the same time, usb 3.0 theoretical bandwidth is 5 gbps, but the data is sent between devices using 8b/10b encoding, which means for every 8 bits of actual data, you have 2 bits of stuff, so only 80% of 5 gbps is actually theoretically possible, or 4 gbps. Then, the device has to arrange data in packets an there's some limitations about how many packets can be sent, how much size can each data packet be, and each packet has some overhead (framing, signaling etc) ... basically, be happy if you get over 400 MB/s.

So a single pci-e lane is more or less more than enough for a single usb 3.0 used to the maximum.

 

You'd get slower transfer speeds if you access both usb devices at same time.

 

Doesn't matter if the actual edge connector on the card is x4 if the controller chip on the card can only use one pci-e lane anyway.

 

 

Posted

where can i get one of these: https://www.ebay.com/itm/PCI-Express-PCI-E-2-Port-USB-3-0-Front-Panel-19-Pin-Card-Adapter-Converter-Board/253477392142?epid=0&hash=item3b046e0f0e:g:YdIAAOSwgLdaofq8:rk:3:pf:1&frcectupt=true

 

PCI-E x4 card with 2 internal 19 pin USB 3 connectors

 

but with at least an x4 connection

1 USB 3 connection can saturate the x1 v2, let alone 4

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  • Solution

Most if not all usb 3 controllers are designed to use a single pci-e lane ... so you'll have either 500 MB/s or ~ 970 MB/s theoretical connection to the chipset / cpu. However, due to arranging data in packets, you'll probably have 5-10% less of that. 

At the same time, usb 3.0 theoretical bandwidth is 5 gbps, but the data is sent between devices using 8b/10b encoding, which means for every 8 bits of actual data, you have 2 bits of stuff, so only 80% of 5 gbps is actually theoretically possible, or 4 gbps. Then, the device has to arrange data in packets an there's some limitations about how many packets can be sent, how much size can each data packet be, and each packet has some overhead (framing, signaling etc) ... basically, be happy if you get over 400 MB/s.

So a single pci-e lane is more or less more than enough for a single usb 3.0 used to the maximum.

 

You'd get slower transfer speeds if you access both usb devices at same time.

 

Doesn't matter if the actual edge connector on the card is x4 if the controller chip on the card can only use one pci-e lane anyway.

 

 

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