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

Martin-123 wrote:

This is very disappointing! ... but thank you, ku4hx.

... so on the Late 2015 model do you just live with 559Mb/s or have you found a work-around?

Thunderbolt 2, "a dead issue" ...? Can you say a bit more about it please...?

I have a late 2015 iMac also. The USB 3 ports are generally plenty fast for what that computer is capable of doing.

I was interested in making use of the Thunderbolt 2 ports so I obtained a Thunderbolt 2 to 4 adaptor and also an inexpensive powered Thunderbolt 4 hub from OWC. They were on special for about $100, it offers multiple USB-C compatible and Thunderbolt 4 ports and even another USB 3 port. So with the Thunderbolt 2 to 4 adaptor in combination with the powered Thunderbolt 4 hub, one can connect multiple USB-C or Thunderbolt 3 (or 4) devices to the iMac through the powered hub. It has to be a powered hub because cause that adaptor doesn't carry power, so the hub needs its own power. This is not an issue for a desktop computer like an iMac, but might be inconvenient for a laptop in such a setup.

The speed of all the devices will be Thunderbolt 2 speed (not Thunderbolt 4) but that is is still 20 Gb/s, faster than the iMac can keep up with.

With this setup, I have the original 4 USB 3 (5 Gb/s) ports in the back of the iMac, plus three Thunderbolt 4 (or USB-C) ports in the hub (20 Gb/s at Thunderbolt 2 speeds), plus another USB 3 port in the hub. There remains an unused Thunderbolt 2 port on the iMac but since Thunderbolt 2 devices aren't available anymore, that just doesn't get used. But this expands the number of connections available way beyond anything I can actually use.

P.S. OWC MacSales still offers the inexpensive Thunderbolt 4 hub (powered, which is what you need) and also sells the Apple Thunderbolt 2 to 4 adaptor that would enable you to connect a Thunderbolt 4 hub to one of your Thunderbolt 2 ports on the back of your iMac, like I did with mine. That gets you 20 Gb/s for any USB-C device connected to that hub.

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

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

Martin-123 wrote:

It sounds like exactly what I'm looking for, Steve. Thank you again, but what about this...

"... but that is is still 20 Gb/s, faster than the iMac can keep up with."

... confuses me a bit. Sorry for my lack of knowledge. Could you say what you mean by that please? Is it just a joke on Apple...?

Depending on your RAM, an older Mac like that and its peripherals (external drives, e.g.)( can only process data and information so fast. Probably the most intensive applications would be high speed video editing and processing, and what I meant was that the throughput of an older Mac like ours in real life intensive applications would top out before reaching the 20 Gb/s limitation of the external connection. So using this setup means your flow is limited primarily by the processing ability of the computer and its peripherals, not by the speed of the external connections to the large data files.

A simple example would be doing a backup to an external SSD through this 20 Gb/s (which is like ~ 2.5 GB/s) connection. Let's say your external SSD is capable of 1 GB/s, which is a very fast SSD. You will never be limited by your 20 Gb/s (2.5 GB/s) connection because the external SSD can't go faster than 1 GB/s. When I do Time Machine backups or SuperDuper backups to such external SSDs, the fastest I have ever seen in practical use is about 1 GB/s, even though the device is actually rated faster. So I have never bumped up against that 20 Gb/s (2.5 GB/s) limit of the Thunderbolt 2 port. The Time Machine or SuperDuper application has to do many calculations and file manipulations during the backup, that slows down the throughput to below the fastest that the Thunderbolt 2 can support.

I think instead of saying "that is is still 20 Gb/s, faster than the iMac can keep up with" I should have said "that is is still 20 Gb/s, faster than the iMac+external_peripherals can keep up with"

By the way, you would be fine without the Thunderbolt hub and its additional cost, using instead the built in USB 3 ports. USB 3 on that Mac gets 5 Gb/s, which is about 600 MB/s, and that's really fast for almost anything. The reason I got the Thunderbolt 4 hub and adaptor was to prove to myself that I could maximally exploit all the external ports on this old iMac, even the Thunderbolt 2 ports (which are obsolete but can still be utilized with said adaptor).

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.

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.

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

You're welcome.

Make sure that you order or buy one that is High Speed USB 3.1 with a blue USB-A end.

Hi,

I just wonder if USB-C to Thunderbolt adapter doesn't work for your purposes.

they show the speeds here

USB-C vs. Thunderbolt: What's the Difference? (lifewire.com)

the slowest device of the 2 set the pace