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How thunderbolt 3 USB-C is able to provide 40 Gbit/s?

455 views 6 replies 2 participants last post by  Mohammednt0 
#1 ·
According to Thunderbolt site they claim that TB3 can provide speed Up To 40 Gbit/s !

But TB3 USB-C is configured with 4 PCIe lane designs which can provide only 32 Gbit/s ! (according to wikipedia)

So there is a bottleneck here !! TB3 USB-C should not be able to throughput more than 32 Gbit/s so how they are saying 40 Gbit/s !?
 
#2 · (Edited)
Yes 40 Gigibits per second max
but not from just the PCIE which as you so correctly say is 4 x 8G

However the Thunderbolt3 using the USB 3.1 type C connection (4 data lanes) allows you to aggregate the 4 10Gbps - 40 Gbps with other protocols

So as on here
In the Thunderbolt mode, Thunderbolt 3 port has the ability to
support at least one or two (4 lane) DisplayPort interface(s) and up to 4 lanes of PCI Express Gen 3

For short details see here
https://thunderbolttechnology.net/consumer/

with a PDF of FULL details
https://thunderbolttechnology.net/sites/default/files/Thunderbolt3_TechBrief_FINAL.pdf

And if you cannot be bothered reading that many pages the short explanation is
Four lanes of PCI Express Gen 3 operate at (4 x 8 Gbps) 32 Gbps roughly.
Thunderbolt 3 uses PCIe x4 gen 3 data rate with 128kB header sizes.
For a single Thunderbolt chip with two ports, the x4 PCIe interface data rate is shared across the ports.
Two links of (4 lane) DisplayPort 1.2 consume 2x (4 x 5.4 Gbps) or 43.2 Gbps.

For both of these numbers, the underlying protocol uses some data to provide encoding overhead which is not carried over the Thunderbolt 3 link reducing the consumed bandwidth by roughly 20 percent (DisplayPort) or 1.5 percent (PCI Express Gen 3).
But regardless, adding both together gets you above 40 Gbps.
 
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#3 ·
Do you still need help
A reply from you would be appreciated
 
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#4 · (Edited)
Good Day,

sorry for the late reply, and thank you for your time in answering my question , i took some time reading and understanding that document
your explanation is great, smooth answer, thanks a lot , the document was very helpful

According to the document:

# Four Lanes of PCI Express Gen 3 can throughput up to 32 Gbit/
# 8 lanes of DisplayPort 1.2 (HBR2 and MST) can throughput up to 43.2 Gbit/s

so thunderbolt 3 will borrow 8 Gbit from DisplayPort 1.2 lanes to complete the maximum speed of Thunderbolt 3 which is 40 Gbit/s is that correct understanding ?

another thing i would like you to explain it to me if you don't mind, thunderbolt 3 usb-c can output in theory 75.2Gbit/s ( 32 Gbit/s & 43.2 Gbit/s ) !! but from what i understand, thunderbolt 3 protocol cannot handle that speed it will only handle 40Gbit/s as maximum speed is that a correct understanding ?
 
#6 ·
The answer as far as I am aware is YES max 40Gbps
 
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