PORTS Forum

Ports and Interfaces => USB => Topic started by: tkafafi on March 20, 2012, 07:50:39 pm

Title: USB3 devices show improved performance in usb2 hosts !!
Post by: tkafafi on March 20, 2012, 07:50:39 pm

According to the bench marking done in http://www.anandtech.com/show/4523/usb-30-flash-drive-roundup/8
 a. pluging a usb3 flash drive into a usb2 host does achieve performance improvement (over usb2 flash drive)
 b. but plugging a usb2 flash drive into a usb3 host doesn't achieve any performance improvement (over usb2 host).

Why is that ?
I would have expected both host and device need to be usb3 (superspeed) to see any improvement in read/write performance?

Thanks

Title: Re: USB3 devices show improved performance in usb2 hosts !!
Post by: Jan Axelson on March 20, 2012, 09:18:55 pm

Devices and host-controller drivers have some latitude in how they implement the relevant USB specifications. It looks like the USB 3.0 drives tested were a little more efficient at high speed than the USB 2.0 drives tested.

Jan

Title: Re: USB3 devices show improved performance in usb2 hosts !!
Post by: tkafafi on March 23, 2012, 06:12:14 pm

Thanks Jan.

Regarding the improved usb3 driver efficiency, could it be due to the new UASP protocol ?
I.e do you think the new drivers are able to run UASP over the legacy EHCI/OHCI controllers? In that case the USB3 sticks are running the newer protocols of USB3 but not the newer 5Gbs speed. Or do you think the new drivers are efficient in some other way ?

Thanks

Title: Re: USB3 devices show improved performance in usb2 hosts !!
Post by: Jan Axelson on March 25, 2012, 12:31:19 pm

If it's a small improvement, it's probably just more efficient code.

Jan