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I bought an external 500GB hard drive with cable that has one end normal micro USB and the other end is split into two regular USB connectors. I have Mac Book Air, which has only one USB port on each side. Is it sufficient to connect the hard drive with only one USB (so I can use regular cable, not the one enclosed)? The hard drive works while connected with only one USB. Do I suppose correctly that it only effects the speed of the data transmission?

Thank you for answers.

  • You're probably fine, but if you drive is under powered you could experience data corruption. I would suggest checking the manufacterer website to see if it lists the power requirements, and then the Apple site to see if you can find how much power your port is capable of providing (if it even says). – Robin Hood Sep 9 '14 at 21:14
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    You might be able to connect the second USB to an Apple mobile device or USB cell phone charger. I stress might. Try this at your own risk with an old throwaway drive if possible. – LawrenceC Sep 9 '14 at 22:19
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The second port is for additional power. Some PCs can't provide enough power on a single port.

If your drive works on your PC with one port, you're okay. No difference in transmission speed or performance.

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Normally the 3 1/2 inch hard drives need the second USB for additional power whereas the 2 1/2 inch external HD's do not need the second USB

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By your description the so called Y-cable is to provide additional power, since USB-Ports (up to USB 2.0) should provide only up to 500 mA (at least that is what USB specifications say, many USB ports do otherwise). So as already pointed out you should check the power rating of the MacBook's USB ports.

I've got a 2,5" external HD (USB 2.0) working with just one USB connector only while using very short cables (less than half a feet). Otherwise you need the Y-cable. The difference between working and not working is quite easy to determine. If underpowered the HD usually does not spin up properly - (in my case just making nasty click-click sounds).

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