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And then there's this: http://www.macrumors.com/2016/10/28/macbook-pro-tb3-reduced-pci-express-bandwidth/ http://www.macrumors.com/2016/10/28/macbook-pro-tb3-re

by 0x0 10y ago

And then there's this: http://www.macrumors.com/2016/10/28/macbook-pro-tb3-reduced-pci-express-bandwidth/ http://www.macrumors.com/2016/10/28/macbook-pro-tb3-reduced-... "MacBook Pro (13-inch, Late 2016, Four Thunderbolt 3 Ports) The two right-hand ports deliver Thunderbolt 3 functionality, but have reduced PCI Express bandwidth."

colejohnson66 10y ago
Wasn't USB supposed to be the connector to rule them all? Now it seems we're going backwards where just because you have a connector doesn't mean it supports what you want.
- user5994461 10y ago
  We are not going backwards. Only Apple is.
- stormbrew 10y ago
  That was always going to be the end result of a single connector standard. Not all devices are going to support all modes of use. In the end, what's really going to dictate how this shakes out is what chipset manufacturers decide to do. And there aren't as many of those as there used to be. Most likely, eventually, all intel chipsets are going to do thunderbolt 3 over usb type-c and everyone else will follow.
  - Cyph0n 10y ago
    Exactly. Bluetooth for example is the same: there are loads of different authentication and communication schemes depending on the device used. The difference of course is that it's mainly the designer who has to worry about it.
cygned 10y ago
> Things only Apple can do
blumentopf 10y ago
Yes, because the PCIe root complex in the CPU can only connect one other device besides the southbridge, and that's used for the Thunderbolt controller on the left handside. The second Thunderbolt controller is connected to the southbridge (as are all the other PCIe peripherals), so it doesn't have the same number of PCIe lanes available as the one directly connected to the root complex. Apple could have solved this by connecting a PCIe switch to the root complex and attaching both Thunderbolt controllers below it, but that would have consumed additional energy. Alternatively they could have used a beefier CPU with more PCIe root ports on the CPU, but I guess those available would have been too energy hungry. Which kind of means this is Intel's fault for not providing a low-energy chip with enough PCIe root ports on the CPU. I'm wondering what the situation is like on the 15" version with discrete graphics. This would require 3 root ports directly on the CPU to drive both Thunderbolt controllers and the GPU with full speed, I assume that's indeed the case since it's not mentioned in the document. Another thing not mentioned in the document is that energy consumption will be suboptimal if one device is attached on both sides of the machine because it prevents one of the Thunderbolt controllers from powering down. One should connect both devices on one side to improve battery life. Edit: On Skylake the PCH is apparently optional, the functionality is mostly integrated into the CPU, so the limitation is really the number of lanes provided by the CPU, and this wasn't sufficient to connect both Thunderbolt controllers with 4x. The CPUs used in the 13" model all have 12 lanes, the ones in the 15" model have 16 lanes. So for the top-of-the-line model this could be 4x for each of the Thunderbolt controllers, 4x for the GPU, 2x for the SSD, 1x for Wifi, 1x for HD Audio?
- revelation 10y ago
  Full Thunderbolt 3 for all four ports on the 15"? I mean, I'm not sure how you can get 40 GBit/s with 4x PCIE 3.0 in the first place, every quote I find says 32 GBit/s. Maybe there is that much overhead in Thunderbolt. But surely 4x40 Gbit/s would require 16 lanes at least. I don't think Intel makes any consumer CPUs with more than 16.
  - Klathmon 10y ago
    What do you mean by consumer CPUs? I've got an ivybridge i7 with 40 lanes right now in my system.
dewiz 10y ago
Apple has a "long" history of differentiating ports by left and right (e.g. https://news.ycombinator.com/item?id=12711127 https://news.ycombinator.com/item?id=12711127) which has been frustrating to me. For instance sometimes the left USB port "dies" after a sleep, while the right one keeps working. I agree it's going to be a mess for a long while, similar to HDMI cables that work or don't without any clear reason for the casual buyer.

by 0x0 10y ago

colejohnson66 10y ago

Wasn't USB supposed to be the connector to rule them all? Now it seems we're going backwards where just because you have a connector doesn't mean it supports what you want.

user5994461 10y ago
We are not going backwards. Only Apple is.
stormbrew 10y ago
That was always going to be the end result of a single connector standard. Not all devices are going to support all modes of use. In the end, what's really going to dictate how this shakes out is what chipset manufacturers decide to do. And there aren't as many of those as there used to be. Most likely, eventually, all intel chipsets are going to do thunderbolt 3 over usb type-c and everyone else will follow.
- Cyph0n 10y ago
  Exactly. Bluetooth for example is the same: there are loads of different authentication and communication schemes depending on the device used. The difference of course is that it's mainly the designer who has to worry about it.

cygned 10y ago

> Things only Apple can do

blumentopf 10y ago

Yes, because the PCIe root complex in the CPU can only connect one other device besides the southbridge, and that's used for the Thunderbolt controller on the left handside. The second Thunderbolt controller is connected to the southbridge (as are all the other PCIe peripherals), so it doesn't have the same number of PCIe lanes available as the one directly connected to the root complex. Apple could have solved this by connecting a PCIe switch to the root complex and attaching both Thunderbolt controllers below it, but that would have consumed additional energy. Alternatively they could have used a beefier CPU with more PCIe root ports on the CPU, but I guess those available would have been too energy hungry. Which kind of means this is Intel's fault for not providing a low-energy chip with enough PCIe root ports on the CPU. I'm wondering what the situation is like on the 15" version with discrete graphics. This would require 3 root ports directly on the CPU to drive both Thunderbolt controllers and the GPU with full speed, I assume that's indeed the case since it's not mentioned in the document. Another thing not mentioned in the document is that energy consumption will be suboptimal if one device is attached on both sides of the machine because it prevents one of the Thunderbolt controllers from powering down. One should connect both devices on one side to improve battery life. Edit: On Skylake the PCH is apparently optional, the functionality is mostly integrated into the CPU, so the limitation is really the number of lanes provided by the CPU, and this wasn't sufficient to connect both Thunderbolt controllers with 4x. The CPUs used in the 13" model all have 12 lanes, the ones in the 15" model have 16 lanes. So for the top-of-the-line model this could be 4x for each of the Thunderbolt controllers, 4x for the GPU, 2x for the SSD, 1x for Wifi, 1x for HD Audio?

revelation 10y ago
Full Thunderbolt 3 for all four ports on the 15"? I mean, I'm not sure how you can get 40 GBit/s with 4x PCIE 3.0 in the first place, every quote I find says 32 GBit/s. Maybe there is that much overhead in Thunderbolt. But surely 4x40 Gbit/s would require 16 lanes at least. I don't think Intel makes any consumer CPUs with more than 16.
- Klathmon 10y ago
  What do you mean by consumer CPUs? I've got an ivybridge i7 with 40 lanes right now in my system.

dewiz 10y ago

Apple has a "long" history of differentiating ports by left and right (e.g. https://news.ycombinator.com/item?id=12711127 https://news.ycombinator.com/item?id=12711127) which has been frustrating to me. For instance sometimes the left USB port "dies" after a sleep, while the right one keeps working. I agree it's going to be a mess for a long while, similar to HDMI cables that work or don't without any clear reason for the casual buyer.