Late 2015 iMac. Fastest Data Transfer from new USB-C devices

Hello, Thank you if you can help...


After much researching, I still cannot establish which is the fastest port on my iMAC AND from which there is an adaptor to accept new USB-C devices.


For some reason the vast majority of adapters are the wrong way round, ie, they will connect multiple connector types, female, to USB-C, male, but not vice-versa. ... as if they cater for connecting old devices to new computers, and not old computers to new devices!


... any suggestions please...?


TIA.




iMac 27″, macOS 10.13

Posted on Sep 7, 2023 4:09 AM

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Question marked as Best answer

Use USB-C to USB-A adapters in the iMac's USB 3 ports.



have a look at > usb-c to usb-a adapters

Posted on Sep 7, 2023 5:18 AM

2 replies
Question marked as Helpful

Sep 7, 2023 8:58 AM in response to Martin-123

Why disappointing? 559 MB/s is very good for an old soon-to-be obsolete device. When I was booting from an external T7 drive, the machine was a pleasure to use. You have to accept limitations, and this is it for that model.


TB2 is just not a viable option. I found some equipment that was advertised to work in 2020, but at 5x the cost of a USB-A device it was not practical. The cables themselves can run $50US and you have to make sure you steer clear of Display Port cables as they have the same connectors. OWC used to sell TB2 gear, but a search of their site returns nothing today.


If you can find the gear and are willing to pay the price, then by all means do so.

22 replies

Sep 7, 2023 8:28 AM in response to Martin-123

My real world experience on that very model is the USB-3 ports are running at 559 MB/s this very moment and the Thunderbolt 2 ports are a dead issue.


The port controls the speed regardless of adapters used. The same is true on our 2020 27" iMacs ... USB 3 559 mB/s. The USB-C ports allow about 1030MB/s.


These are speeds associated with Samsung T7 SSDs which have a Mac advertised speed of 1050MB/s

Question marked as Helpful

Sep 7, 2023 8:58 AM in response to Martin-123

Why disappointing? 559 MB/s is very good for an old soon-to-be obsolete device. When I was booting from an external T7 drive, the machine was a pleasure to use. You have to accept limitations, and this is it for that model.


TB2 is just not a viable option. I found some equipment that was advertised to work in 2020, but at 5x the cost of a USB-A device it was not practical. The cables themselves can run $50US and you have to make sure you steer clear of Display Port cables as they have the same connectors. OWC used to sell TB2 gear, but a search of their site returns nothing today.


If you can find the gear and are willing to pay the price, then by all means do so.

Sep 7, 2023 1:38 PM in response to Martin-123

Re: “Thunderbolt 2, "a dead issue" “


Thunderbolt 1 & 2 use the Mini DisplayPort connector. Seeing the work on USB-C, Intel decided that Thunderbolt would gain more traction by becoming an ALT mode on USB-C than by staying on the Mini DisplayPort connector.


So you need a $50 adapter to go between TB 3 or 4, and TB 1 or 2. That adapter does not carry power, so you cannot use it to plug a bus-powered TB 3 SSD directly into a TB 2 equipped Mac.

Late 2015 iMac. Fastest Data Transfer from new USB-C devices

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