Comment by Dylan16807
4 years ago
> 3m is beyond the max cable length specified by Thunderbolt, so it requires active extenders (they're hidden in the plugs) and tight manufacturing and shielding. You're paying extra for the ability to break that max length spec, and it's one of only a handful of products that do it.
I'm pretty sure it's not breaking the spec. Are you sure about that claim?
And the main factor is almost always decibels of signal loss rather than length, isn't it?
> Also those Corning cables have a reputation for failing barely out of warranty even if they are treated very delicately. Amazon reviews are full of "my cable failed 1 year and 1 month after purchase and Corning told me to go eat a dick" type reviews.
My understanding is that the thunderbolt 2 ones reliably self-destruct but the thunderbolt 3 ones probably fixed it? At the very least they can take a lot of physical abuse.
> 10gbps half-duplex USB 3.1 cable
I don't think any of the high speed wires are ever half duplex?
> I'm pretty sure it's not breaking the spec. Are you sure about that claim?
Actually we're both wrong... it appears max length for a passive cable is 18 inches for full performance. Passive cables technically max out at 18 inches for 40gbps and drop to 20gbps at 2 meters. Past that you need an active cable (which has signal repeaters).
Active cables generally run up to 2 meters (the Apple is the first 3m active cable except for the Corning AOC cables), but in most cases (everyone except apple) you start dropping features like USB 3.1 or displayport. AFAIK Apple's solutions are unique in that they don't - like for example I looked up a 2 meter Belkin cable advertised as TB3 and it doesn't carry the DisplayPort channel.
Which is why the advice for Thunderbolt is "just shut up and pay apple their money".
https://appleinsider.com/articles/17/08/15/psa-thunderbolt-3...
Not absolutely positive what the official standard is - they might well only say the passive number (ie 18 inches) because active can obviously be more or less arbitrarily long with things like fiber, it might not make sense to define a maximum cable length in that context. Or they might amend it as they go... obviously Apple has now broken the 2 meter barrier with their active copper cable.
I thiiiiink this becomes 0.8m for a passive cable in USB4/TB4 as the official passive spec? CableMatters seems to have a 2 meter active cable out though.
> I don't think any of the high speed wires are ever half duplex?
High-speed is half-duplex, yeah. It looks like SuperSpeed is full-duplex though so I'm wrong on that bit.
I just remember it being a nightmare trying to use USB external hard drives (which would have been back in the USB 2.0/High-speed era when I used them last!) and reading/writing at the same time tanked performance far beyond what you'd get with even an internal HDD. Read or write, one at a time, mixing both was a trip to hell.
https://www.ramelectronics.net/USB-3.aspx
> Actually we're both wrong... it appears max length for a passive cable is 18 inches for full performance. Passive cables technically max out at 18 inches for 40gbps and drop to 20gbps at 2 meters. Past that you need an active cable (which has signal repeaters).
I'm still pretty sure it's based on signal loss, and the lengths are just estimates of what you can reliably get out of a cost-optimized manufacturing process.
> High-speed is half-duplex, yeah. It looks like SuperSpeed is full-duplex though so I'm wrong on that bit.
By "the high speed wires" I mean the pairs introduced with USB 3. Not USB's dumb naming conventions.
> I just remember it being a nightmare trying to use USB external hard drives (which would have been back in the USB 2.0/High-speed era when I used them last!) and reading/writing at the same time tanked performance far beyond what you'd get with even an internal HDD. Read or write, one at a time, mixing both was a trip to hell.
I think a big part of that is also the mass storage protocol combined with slow responses off a hard drive. I have a USB 2.0 SSD-class drive around here and it actually performs pretty well even on mixed workloads.
> for example I looked up a 2 meter Belkin cable advertised as TB3 and it doesn't carry the DisplayPort channel
It’s not possible (I think?) for a USB-C cable to support TB3 but not DisplayPort. Both are alt modes on the USB protocol and use the same wires for transmission, so it doesn’t make sense to go the extra mile of TB certification and not support DP too when you already have the necessary wires.