How many external devices can I connect to iMac?

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Level 1

8 points

How many external devices can I connect to iMac?

Hey guys,

I am having some issues here. I know that theoretically an USB bus can allow you connect 127 devices. Now I have some external hard drives and some USB devices connected to my computer:

2 x 6TB drives,

1 x 8TB drives,

3 x 12TB drives,

2 x 16TB drives (Just got),

1 x USB keyboard,

1 x Sound card,

1 x SuperDrive,

1 x Microphone,

1 x Bluetooth Magic mouse.

I am using two 7-ports 35 watt powered USB 3.0 hubs. So two devices are directly connected to iMac. The rest of them is connected two these hubs.

I just got two new 16 TB hard drives yesterday. But when I connect them to iMac directly or USB hubs. There are always some devices not recognized. Even if they are all recognized, the USB hub ports indicator will go off and I lose all the connections (including keyboard and mouse).

Any ideas what's happening here? Many thanks.

iMac, OS X El Capitan (10.11.6), 2014 iMac

Posted on Mar 27, 2017 7:06 PM

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Answer 1

dwb

Level 7

33,244 points

Mar 28, 2017 7:00 AM in response to Tixiao

Tixiao wrote:

Even if they are all recognized, the USB hub ports indicator will go off and I lose all the connections (including keyboard and mouse).

Perhaps the USB hub indicator lights going off is a hint. The problem might be the hub or the hub power supply. Since the hub will supply power to devices that aren't powered with a brick perhaps there's a bad brick (or two or three).

You have more things plugged into your computer than I do - 4 more than I do - but I've known people with more. So I suspect you have a device that is messing up the works. Good luck.

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Answer 2

BDAqua

Level 10

250,259 points

Mar 28, 2017 2:00 AM in response to Tixiao

In System Report, check available & used mA...

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Answer 3

Tixiao Author

Level 1

8 points

Mar 28, 2017 5:40 AM in response to BDAqua

Thanks for the reply. I did check the available current. However, most of my devices are self-powered. So are my USB hubs. The "current required" shown on my iMac are mostly zero.

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