I’m considering pre-ordering the new M4 iMac (the model with 4 Thunderbolt 4 ports). I use a lot of SSD space and rely on having external drives connected. Currently, I’m using a couple of Samsung T7 Shields and a Jeyi 2464PD, all with 4 TB capacity. They are connected via Thunderbolt/USB 4 and the USB-C port on my iMac M1. The Samsung T7 SSD doesn’t meet the promised 1 GB/s (I get about 600 MB/s). My Jeyi performs as expected. Will the new Thunderbolt 4 ports perform better, especially regarding USB 3.1 Gen 2 SSDs?
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iMac M4 TB speed.
- Thread starter mogens
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So you have the M1 8GPU w/ 2xTB4 and 2xUSB3 USB-C ports? Won’t know until people can test new M4 iMac TB4 ports, but I suspect the same lack of support for USB Gen 2 dual-lane (x2) to exist.
Yes, the "big" M1 iMac. I read somewhere that Thunderbolt 4 can handle USB 3.1 Gen 2 (10 Gbps) and USB 3.2 Gen 2x2 (20 Gbps) devices. But you never know with Apple.
You don't have to wait for testing in regard to USB 3.2 Gen 2x2 (20Gb/s).
It's right there on Apple's Tech Specs page:
Four Thunderbolt 4 ports with support for:
Because TB4 and full USB4 exceed it, rendering it unnecessary.
The sub-standard performance of directly attached USB 3.1 Gen 2 SSDs on the early M1 Macs is well documented in these forums.*
Probably because the M1 was a Gen V1.0 product, with some minor incompatibilities.
Which was irrelevant in practice as M1 TB4 works faultlessly.
* The work around is to connect USB 3.1 Gen 2 SSDs to a TB3 dock** (preferably using Intel's Titan Ridge controller chip, post 2018). A cheap pre-used one will work fine as it will have been Intel certified.
** Not a TB4 dock, as these work differently.
It's right there on Apple's Tech Specs page:
Four Thunderbolt 4 ports with support for:
- Thunderbolt 4 (up to 40Gb/s)
- USB 4 (up to 40Gb/s)
- USB 3.1 Gen 2 (up to 10Gb/s)
- DisplayPort
Because TB4 and full USB4 exceed it, rendering it unnecessary.
The sub-standard performance of directly attached USB 3.1 Gen 2 SSDs on the early M1 Macs is well documented in these forums.*
Probably because the M1 was a Gen V1.0 product, with some minor incompatibilities.
Which was irrelevant in practice as M1 TB4 works faultlessly.
* The work around is to connect USB 3.1 Gen 2 SSDs to a TB3 dock** (preferably using Intel's Titan Ridge controller chip, post 2018). A cheap pre-used one will work fine as it will have been Intel certified.
** Not a TB4 dock, as these work differently.
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There will be no speed gain. There will only be a stable speed at “peak load”. Since you will be stymied by the SSD disk bus bandwidth capabilities. Plus, you can't get around parasitic disk buffering during fill, where the speed drops dramatically when it reaches a plateau.
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