M1 Thunderbolt ports don’t fully support USB 3.1 Gen 2

The inability of the USB standards body to stick to a versioning scheme beggars belief: what in the world could "USB 3.1 Gen 2" possibly mean? Versions are free, why not simply name it "USB 3.2" and make the next one 3.3?

"Gen 2" strikes me as the "Essay FINAL (final version 2).docx" of standards revisions.

Re: M1 Thunderbolt ports don’t fully support USB 3.1 Gen 2

#6

Post by nikanj » Mon, Apr 18, 2022, 9:54 AM UTC

USB went from being the universal bus, to just being the universal connector. There are never any guarantees that your device (or cable!) actually supports the operation you’re trying

Re: M1 Thunderbolt ports don’t fully support USB 3.1 Gen 2

#7

Post by LeoPanthera » Mon, Apr 18, 2022, 9:55 AM UTC

mlindner wrote: post #2

My initial suspicion would be the user used bad cables. There's many cables that say they're capable of a speed when they are not in fact capable.

If that was the case, the front non-thunderbolt ports would not be faster, but they are.

Re: M1 Thunderbolt ports don’t fully support USB 3.1 Gen 2

#8

Post by RedShift1 » Mon, Apr 18, 2022, 9:55 AM UTC

chrisseaton wrote: post #3

> In normal testing, 5 Gb/s should yield around 500 MB/s Wow 90% overheads?

5 gigabit/s = 0.625 gigabyte/s = 625 megabyte/s

so about 20% overhead... I would not be dissatisfied with 500 MB/s result on a theoretical 625 MB/s bus.

Re: M1 Thunderbolt ports don’t fully support USB 3.1 Gen 2

#9

Post by tjoff » Mon, Apr 18, 2022, 9:55 AM UTC

jon_adler wrote: post #4

chrisseaton wrote: post #3

> In normal testing, 5 Gb/s should yield around 500 MB/s Wow 90% overheads?

Bits to bytes means dividing by 8.

Just to add for clarity, b is used for bits and B for bytes. Though they are often mixed up.

(... and a byte is not always 8 bits)

Re: M1 Thunderbolt ports don’t fully support USB 3.1 Gen 2

#10

Post by mlindner » Mon, Apr 18, 2022, 9:57 AM UTC

LeoPanthera wrote: post #7

mlindner wrote: post #2

My initial suspicion would be the user used bad cables. There's many cables that say they're capable of a speed when they are not in fact capable.

If that was the case, the front non-thunderbolt ports would not be faster, but they are.

If the cable is wrecking signal integrity, the port could absolutely change things if the ports have slightly different hardware that's generating the signal. RF does weird things.

Just as a very simplistic analog DC example, if you have wires that are both sitting at 3V but one can only drive 100 mA while the other can drive 1A. If you only draw 50 mA they'd look near identical but as soon as soon as you tried to get close to 100 mA they'd both diverge heavily. You could advertise both at 50 mA for sales purpose but if they were hooked up with a bad high resistance cable they'd look very different.