External USB 3.0 runs at 2.0 speeds on Bootcamped (L)2013 27" iMac

[Edan]

Hi, I recently boot camped my late 2013 27"iMac with Windows 8.1. I've noticed that my external harddrive has a transfer rate of 25-36mb/s for a USB 3.0 external (1tb Samsung M3 Portable USB3.0 External Harddrive). I'm not too certain what the cause is, but if anyone knows how I can get 3.0 speeds would be greatly appreciated. - I have an Internal 256 SSD
Thanks!

( I did try to reinstall Boot Camp Assistant again and install but it didn't resolve the issue
Also checked device manager - shows standard USB Controllers, one relevant is 'Intel(R) USB 3.0 eXtensible Host Controller - 0100 (Microsoft).
I've tried to see if there is a driver update for that specific one, however it says its the most up to date version with a controller showing 'USB xHCI Compliant Host Controller'.)

 

[DeltaMac]

Does your external USB HD show USB 3 connection when you are booted to OS X?
You can check that in your System Information/USB tab.

 

[Edan]

It shows under speed: 480 mb/sec when run on OS X
Not sure how to see what it can run at when on 8.1? I tried transferring files to and from the external hard drive on 8.1 and the highest I've seen it reach is 39mb/s