I've got a USB 2 5400 RPM external HD. I'm thinking of getting a new computer with USB 3 ports.
If I'm currently getting read/write speeds from the external HD on USB 2 of roughly 30 mb/s (both read and write), then would upgrading to USB 3 make a difference? Since USB 2 is roughly 480 mbps (60 mb/s), which is more than the 30 mb/s I'm getting now, then won't it technically make no difference at all?
Specifically, the drive I have is this very popular one.
Answer
The reason USB 2.0 is practically limited to roughly 50% if it's rated speed (20-30MB/s vs. 60MB/s) is that is not full-duplex, thus every data packet which comes to the host (PC) will need another packet to the device (HDD), effectively limiting the speed to ½ of the theoretical 480MBit/s.
Since USB 3.0 has not only much higher rated transfer speeds, but also allows full-duplex operations, you can expect to see almost maximum device speed (usually around 90-130MB/s).
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