On Thursday, December 5, 2013 12:37:26 AM UTC-6, Paul wrote:
Andy wrote:

On Wednesday, December 4, 2013 10:06:42 PM UTC-6, Paul wrote:

Andy wrote:



What factor of my system is necessary to be able to use the full speed of a USB 3.0 card ?

Thanks.





USB3 can be provided two ways. It can be



provided by the main chipset (some Intel chipsets,



chipsets like AMD A75 - Wikipedia can give you a list).







Or, for the majority of people, USB3 comes from



a standalone chip made by NEC, Etron, Asmedia, and so on.







With those chips, there is a tendency to put a PCI



Express single lane interface. That's PCI Express x1.



Doing so, saves pins on the chip, and reduces chip cost.



That's how you can sell a $25 USB3 PCI Express card.







Motherboards have several kinds of PCI Express slots,



but we'll concentrate on the PCI Express x1 ones.







PCI Express Rev 1.1, x1 lane = 250MB/sec



PCI Express Rev 2.0, x1 lane = 500MB/sec







The second of those, does a better job of exposing



all of the USB3 capability. For example, if you



bought a BlackMagic video capture device with USB3



connector, the software for that device actually



tests and verifies that a 500MB/sec lane is present.







There are no other devices I'm aware of, where bandwidth



testing is involved.







So the ideal situations, from best to worst.







1) Chipset USB3 port, with no restriction on the bus



connection to the rest of the chipset. The DMI bus or



Hypertransport bus connection to the Southbridge in



such a case, likely runs 2GB/sec or higher, plenty for



a USB3 stream. You don't have to worry about the



connection being choked off. And as for implementation,



I think the AMD A75 and similar, they didn't design the



USB3 logic block themselves, but bought a design (intellectual



property) from a company making a successful chip.



That means less development cost, to ship a design.







2) Plug an add-in card into a Rev 2.0 slot. You can use



a video card slot for this, if one is available. Some



motherboards have multiple video card slots. You can



plug an x1 card, into an x16 slot. It's a waste, but,



you're getting the best. Video card slots tend to support



Revision 2 or even Revision 3, for the very highest rate



of transfer. No USB3 chip I've heard of, uses PCI Express



Revision 3.







3) Plug an add-in card into a Rev 1.1 slot. This is good



enough for enclosures where the disk enclosure USB3 adapter



chip is limited to 200MB/sec anyway. Such an enclosure,



even if you stuffed a high performance SATA SSD into



the enclosure, it would be the enclosure chip which was



the limiting factor. So in that situation, the low



end and quite common PCI Express x1 slot is good enough.







There is more to PCI Express bandwidth than just the "plumbing



rating". When I quote 250MB/sec, that's raw bitrate on the



lane. The typical chipset has rather small buffers fitted



at the end of the link, and the buffer size can actually



cut the transfer rate in half. You shouldn't assume that



the number printed in the Wikipedia article for PCI Express,



is the final story.







http://www.plxtech.com/files/pdf/tec...yload_Size.pdf







The figure on page 2 there, shows the "efficiency" number.



You multiply the 250MB/sec number by the "efficiency", to



get a better value (trending in the right direction) for



what your x1 lane can actually do. Is it easy to find



out the buffer size of your chipset buffer ? Nope. It's



a trade secret. It would be embarrassing, if everyone



knew their 4GB/sec video card slot, wasn't actually



doing 4GB/sec. The horror.







The UAS protocol here, has a calculated transfer rate



of 336MB/sec. But no device to date has achieved that.



At least for USB storage. Keep your eyes peeled though,



for benchmarks, because some year, they'll fix that.



The last time I checked, the best seemed to be around



200MB/sec or so.







http://www.nordichardware.com/Archiv...idge-chip.html







Plug your new USB3 card into a video card slot... and, enjoy.







It's a good thing the last motherboard I bought, has two



video card slots.







Paul



Thanks.



I have one PCI Express slot.



Could I use that ?



I am happy using the on board video, it only uses 128 Mb and I plan to up my RAM to 4 Gbs.





It's your choice as to what slot you use. The lack of USB3

peripherals that "need the speed", suggests to me that using

the best slot isn't a priority. If you have the BlackMagic

USB3 video capture box, then yes, you'd probably want to

use the best slot available. Or, buy a motherboard that has

native USB3, and not the add-on USB3 type.



Paul

I have a USB 3 external hard drive.

I could use the extra speed for image backups.

Canon camera may also benefit.

Andy