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USB 3.0 High-Speed and SuperSpeed

E

EnigMoiD

macrumors member
Original poster
Aug 10, 2007
99
0
In System Profiler on my 2012 MBA, I see four entries in USB: 3 "USB High-Speed Bus" and one "USB SuperSpeed Bus." When I plug in my iPhone, it appears under a "Hub" entry in the same "High-Speed" bus that has the keyboard and bluetooth controller.

When I plug in my USB 3.0 hard drive, it appears under the SuperSpeed Bus no matter which port I plug it into. So the SuperSpeed Bus must be for actual USB 3.0 devices, and since there is only one "SuperSpeed Bus" and no "Hub" in it, my question is: can the 2012 MacBook Air support two USB 3.0-speed devices, or will one always run at 2.0 speeds?

EDIT: Maybe someone who owns two USB 3.0 hard drives could test this?
 
By definition, USB 2 is called HighSpeed and USB 3 is called SuperSpeed. What you're seeing there is the device manager recognising that a USB 2 device is connected, since USB is backwards compatible. Both ports are connected separately to the chipset so they should be able to utilise USB 3 at the same time. I don't have a 2012 MBA, but I can check later tonight on my rMBP with a couple of USB 3 devices connected at the same time.
 
Apologies for the multiple posts, but it's a lot later.

This is what happens when I connect two USB 3 Patriot flash drives.

2USB3Devices.png


They are both on the correct Superspeed bus

This is when I connect a USB 2 Corsair flash drive in the one port and a Patriot USB 3 flash drive in the other port.

USB3andUSB2.png


I expect the MBA to be working in the same way.
 
Updated Models of MacBook Air were meant to support the two USB 3.0 ports along with high-speed thunderbolt, capable of transferring data at up to 5 Gbps. I suppose that both the USB 3.0 ports should work together. However, I am not sure if one of the port will function as a USB 2.0 Port.
 
shepherd king said:
Updated Models of MacBook Air were meant to support the two USB 3.0 ports along with high-speed thunderbolt, capable of transferring data at up to 5 Gbps. I suppose that both the USB 3.0 ports should work together. However, I am not sure if one of the port will function as a USB 2.0 Port.
Click to expand...

I can't check this on a 2012 MBA, but both ports work at full USB 3 speed on a 2012 MBP.
 
The issue still persists with MBA mid 2013

This thread is old, but the same thing still happens with MBA 11" mid 2013 I just bought.

It looks like my patriot USB 3.0 USB flash is connected to SuperSpeed bus after boot. But if I connect the patriot flash after my iPad 2 (USB 2 device)is connected and disconnected to the same USB port, the patriot flash appears in High-Speed bus. Then it is connected back to the SuperSpeed bus after I reboot my MBA.

I feel like an apple software bug relating to USB version handling for a device supporting both USB 2 and 3 though.
 
You suggested a good point. I tried to test the performance for each case. I transferred 967MB file in the local SSD in my MBA to the patriot flash. The result was below:

In super speed connected, takes 22.88 seconds, meaning 42MBytePerSec 339MBitPerSec
In hi-speed connected, takes 42.76 seconds, meaning 23MBytePerSec 181MBitPerSec

I used stop watch to measure the time, but the differences are enough big, I think.

By the way, I also tried to connect another USB 3.0 hub in the other USB 3.0 port while the patriot flash was connected to the super bus, then I saw the both were connected to USB 3.0 super bus. So it means my MBA is capable to connect 2 USB 3.0 devices to USB 3.0 super bus.
 
I thought this thread complained what I experienced (USB 3.0 patriot flash is connected to hi-speed bus in some cases), but it looks different, just asking if MBA is possible to connect 2 USB 3.0 devices to super speed bus. Sorry about my confusing posts.

But anyway, it looks like MBA mid 2013 should have an issue handling USB versions, I think.
 
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