Two of four Thunderbolt 3 ports in new 13" MacBook Pro with Touch Bar have reduced speeds
A support document published by Apple on Friday reveals only two of the four Thunderbolt 3 ports in the latest 13-inch MacBook Pro with Touch Bar support full-speed data transfer, potentially limiting the notebook's flexibility for power users.
Apple in a Support Pages document covering Thunderbolt 3 connectivity says late-2016 MacBook Pro port data speeds "vary slightly" depending on the model. Of note, the 13-inch version with Touch Bar delivers full PCI Express bandwidth, and thereby lower throughput, to only two of its four ports.
Specifically, the two ports on the notebook's right hand side provide full Thunderbolt 3 functionality, but have reduced bandwidth, while the left pair retains full PCIe throughput. For this reason, Apple recommends connecting high performance peripherals like fast Thunderbolt 3 RAID arrays via the left-hand ports.
By comparison, the more powerful 15-inch MacBook Pro model supports full PCIe bandwidth on each of its four Thunderbolt 3 ports, as does the 13-inch MacBook Pro without Touch Bar for its two ports.
As AppleInsider noted in a deep dive into Thunderbolt 3 earlier today, the new MacBook Pro with Touch Bar models incorporate two Thunderbolt 3 controller chips.
The exact setup remains unclear at this time, but the latest hardware likely employs a version of Intel's Alpine Ridge controller and chipset. Intel currently lists multiple variations of Alpine Ridge in single-port, dual-port and low-energy SKUs, each with a different number of PCIe lanes. A single lane is defined as a pair of unidirectional signaling connections that in a PCIe bus work together to deliver full duplex communication. These lanes determine how much data can flow through a PCIe link, and are likely behind the 13-inch MacBook Pro's specs.
Considering the 13- and 15-inch MacBook Pro with Touch Bar offerings are able to run a 5K display -- two 5K or four 4K monitors on the 15-inch model -- Apple is thought to be using a pair of dual-port controller chips on both versions. What remains unclear, however, is whether the controller chips are identical. From the support document, it appears that either the 13- and 15-inch Thunderbolt 3 controllers have a different number of PCIe lanes or, more likely, that the 13-inch model's bottleneck is external to the chipset.
Apple in a Support Pages document covering Thunderbolt 3 connectivity says late-2016 MacBook Pro port data speeds "vary slightly" depending on the model. Of note, the 13-inch version with Touch Bar delivers full PCI Express bandwidth, and thereby lower throughput, to only two of its four ports.
Specifically, the two ports on the notebook's right hand side provide full Thunderbolt 3 functionality, but have reduced bandwidth, while the left pair retains full PCIe throughput. For this reason, Apple recommends connecting high performance peripherals like fast Thunderbolt 3 RAID arrays via the left-hand ports.
By comparison, the more powerful 15-inch MacBook Pro model supports full PCIe bandwidth on each of its four Thunderbolt 3 ports, as does the 13-inch MacBook Pro without Touch Bar for its two ports.
As AppleInsider noted in a deep dive into Thunderbolt 3 earlier today, the new MacBook Pro with Touch Bar models incorporate two Thunderbolt 3 controller chips.
The exact setup remains unclear at this time, but the latest hardware likely employs a version of Intel's Alpine Ridge controller and chipset. Intel currently lists multiple variations of Alpine Ridge in single-port, dual-port and low-energy SKUs, each with a different number of PCIe lanes. A single lane is defined as a pair of unidirectional signaling connections that in a PCIe bus work together to deliver full duplex communication. These lanes determine how much data can flow through a PCIe link, and are likely behind the 13-inch MacBook Pro's specs.
Considering the 13- and 15-inch MacBook Pro with Touch Bar offerings are able to run a 5K display -- two 5K or four 4K monitors on the 15-inch model -- Apple is thought to be using a pair of dual-port controller chips on both versions. What remains unclear, however, is whether the controller chips are identical. From the support document, it appears that either the 13- and 15-inch Thunderbolt 3 controllers have a different number of PCIe lanes or, more likely, that the 13-inch model's bottleneck is external to the chipset.
Comments
I don't see how they could save money on this. A couple of dollars maybe? The cost for the integration of a different chip set, would seem to offset potential savings.
And it's not something that can be used in marketing either because it's over most people's heads... it will make for unhappy customers AFTER they bought it and realize the limitation. So unless there's a technical reason, this would be a stupid move.
Bad Apple
Processors today use PCIe to connect everything from Storage controllers, high speed I/O like USB, Thunderbolt and other stuff including SD-Card readers and Graphic Cards (or discrete GPU in case of macbook). And on each processor model there is only a specific number of these lanes available. This means that since Apple has to rely on Intel on this issue, they can't simply change this behavior by putting in a second controller, it's simply not possible because there is no dual core i7 Chip with enough lanes. Thats why Apple has chosen to use the PCH-supplied PCIe-Lanes.
PCH is an additional chip (which is integrated directly in the processor package on some models) which connects to the processor via a seperate high speed bus and it gives you many things included USB, keyboard support, audio and storage interface and additional (about half speed) PCIe-Lanes in one single chip. What I think is the case is that Apple is using these lanes because the processor itself does not supply enough PCIe-lanes.
So obviously, there is nothing to be added from a non-technical viewpoint, because it's not about power consumption or other marketing decisions, it's simply because Intel does not make the chips Apple needs for four Thunderbolt 3 full speed capable ports.
Current 13" prices would start making sense if these MacBook Pro models had quad-core CPUs and twice the amount of RAM.
The only model with a dual-core CPUs should have been the one without the Touch Bar, and in its basic configuration it should have been $1199.
What I bet, is that all 4 ports support full speed, but the dual core CPU doesn't have enough PCIe lanes to support running all of them on the dual core, so there's a bridge chip that creates more lanes, but is technically splitting one.
If you look at https://thunderbolttechnology.net/sites/all/themes/tb/images/Thunderbolt3_infographic_100715.jpg
You'll note that the chip itself is 10Gbits, and allows 4 PCIe lanes to go over thunderbolt. So to have 4 ports you need 16 PCIe lanes free. Take note that Skylake only has 16 PCIe lanes from the CPU, and 20 come from the PCH. Now, on the Quadcore models, you also have a dedicated GPU. That means those 16 lanes on the CPU are connected to the GPU, and all the thunderbolt lanes are connected to the PCH.
So if you look at http://ark.intel.com/products/91169/Intel-Core-i7-6660U-Processor-4M-Cache-up-to-3_40-GHz , which is a dual core, what do you see?
12 PCIe lanes.
Versus the top-of-the-line model http://ark.intel.com/products/93336/Intel-Core-i7-6970HQ-Processor-8M-Cache-up-to-3_70-GHz
16 PCIe lanes.
So if this is the kind of thing Apple did, then it's reasonable to believe that the 13" model only has 12 PCIe lanes, so two ports are going to share 4 lanes. That may not be meaningful depending on what you connect to it. Desktop and Server models all have 16 PCIe lanes.
Some dual core models only have 10 lanes (m5 and m7 models.)
the purpose of a portable is to be portable. some professionals don't want to travel with a 15"
Apple needs a 13" *real* pro that can be a smaller, spec-maxed computer.
They provide full bandwidth on all ports yes, but the 13" Pro without Touch Bar only has 2 thunderbolt ports.
New 15" Pro is only marginally bigger and heavier than MBA.
2 ea 40Gb/s Thunderbolt (TB3)
2 ea 20Gb/s Thunderbolt, but still the TB3 spec
That's really cool.
The base 13" MBP has two USB-C ports.