Four PCIe lanes per two TB ports.
Now that would be a normal Thunderbolt 3 port, but the ports on the MacBook Pro are special. They get 4 lanes per port, and it can siphon 8 lanes into a single port to power the 5K 60Hz display, and it can do that to both sides simultaneously as well, allowing you to run 2 5K displays.
This is obviously really powerful technology, which is why it's so darn expensive - but who actually needs this? Very few, I'd wager. I think most people would have been better served with a wider variety of ports, and then those that really want this insane config can go for it as an option, but I honestly don't think anybody would. Buying 2 5K LG UltraFine is very, very expensive.
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Kind of. Maybe "workstation" was the wrong word. "Computer for General Professional Work" would be more accurate. For many types of 'pro' work, the odd error is not going to matter. If it does matter, there should be software-level checks in the maths.
If you need to develop code, you don't need ECC RAM. If you're doing anything in machine learning, the odd error is going to have zero effect. I'd say the vast majority of 'pro' work does not need "workstation" class hardware, with the epic cost premium that comes with it.
And even if they did, Apple does not sell anything below the iMac Pro which can be used for work that does require ECC.
The fact remains that powerful GPUs and CPUs are not only good for games. They are also good for a lot of engineering tasks, video processing, software design (including making games) and anything else that can benefit from more parallel processing. And many of those tasks would benefit from being able to be done on a portable computer.
ECC memory is basically useful if you're running server applications, and that's it. This is also virtually the only space in which Xeon is used in the PC space, and with good reason. It's really expensive and doesn't make sense.
To put into perspective how unnecessarily expensive Xeon and ECC memory is, you can currently get Windows laptops in the ~$1500 range that will outperform the iMac Pro 8 core. Yep, really.
To be fair to the iMac Pro, it's got these server grade features and it's got incredibly powerful graphics and display, but who actually needs an awesome display on their server and, inversily, who actually needs ECC memory and Xeon chips on their development machine?
That's right, virtually nobody.
And this is the great irony of the Apple tax. The machines are not actually overpriced at all. If you actually look into it and add the components up that Apple selected, it turns out there really is no Apple tax at all other than their absurd prices for extra upgrades from the store. However, their component selection is utterly strange most of the time, so you get these machines with all this stuff in them that you just don't need.
And it'd be fine if it was just a few people that didn't need all the features, but generally almost everyone wanted them all. Like giving them all webcams and backlit keyboards and great trackpads etc. etc. This makes sense. Putting a Xeon chip in an iMac, however, does not.