That is what limits write speed and cables needed.

Global Speed used by ALL USB 2.0 devices (and also USB 1.x).

Energy needed (can be more on USB 3 connector).

So while some USB 2.0 DVD units can not be powered by only one USB 2.0 port (they need a Y type cable), putting them on USB 3.0 they may work perfectly without Y type cable, depends on manufacture of the USB 3 port.Īlso some that has a round conector for power (most use a round to USB power cable), some of them while connected with a Y type to USB 2.0 por or just directly to a USB 3, they do not need such 'extra' cable others need an external power supply you must do some tests to know in which case you are. Yes, some USB 3 devices need 20V of power from USB 3 port, so they are not backward compatible with 2.0, but they are very uncommon just because of that. The other point is USB 3 can give a lot more current than 900mA, in some manufactures they reach 100W (20V*5A), while most give only 5V, not 20V.

HDD read must be at least equal or greater to DVD write to not have 'problems' (some readers has problems reading a DVD that has got stops on writes), so USB bus speed (25MiB/s) will allow for only arround 12MiB/s writes and that is only 8X, so if you plan to write at 16X and what you want to write is also on USB 2.0 you will not be able to do it at that speed without buffer underflows. Some points: DVD at 8X writes at 1.32MiB/s * 8 = 10.56MiB/s, not 36MiB/s (36MiB/s is for BluRay at 8X).īut if Read medium is also on USB 2.0 (read from an enclosure and write to an external USB DVD writer) it can saturate USB 2.0 bus speed very easy.

Usb 2 vs usb 3 symbol