Late 2013 Thunderbolt bus

Discussion in 'Mac Pro' started by michael_aos, Mar 15, 2015.

  1. michael_aos macrumors 6502

    Jan 26, 2004
    Late 2013 Mac Pro.

    I have some "Up to" 20 Gb/s x1 and 10Gb/s x2 devices.

    I know if you chain a Thunderbolt 2 device off a Thunderbolt 1 device, you'll only get Thunderbolt 1 speeds.

    My question is whether having both a Thunderbolt 1 and Thunderbolt 2 device on the same bus (i.e. - Bus 1) (since there are 2x Thunderbolt ports on Late 2013 Mac Pro for Thunderbolt Bus 1) will slow everything on the bus down to Thunderbolt 1 speeds?

    Or can, for example, port-1 of Bus 1, communicate at 20Gb/s x1 and port-2 of Bus 1 communicate at 10Gb/s x2?
  2. deconstruct60 macrumors 604

    Mar 10, 2009
    It is same TB controller more so than same "TB bus" (as Apple appears to use the term).

    Pragmatically no in most cases with input/output in both directions, but for a different reason that the limitation when daisy chaining.

    TB ports are not additive. The two ports provisioned by a single controller share the same inputs. If this is encoded PCI-e data traffic even if the "all TB v2.0" chain in port 1 could send data 20Gb/s speeds, the in/outbound data on the other port will eat into the same x4 PCI-e v2 interface the controller has with the host system. ( that shared PCI-e v2 interface and DP inputs being the "TB bus". In that sense yes... but it is really not a Thunderbolt data traffic issue. It is really a getting off the TB network issue. )

    If the TB devices were passing data to one another and not all trying to send it to just one device (e.g., the host computer) then no there not a slow down except as transition to a v1 device.

    Same with daisy chain. host <--> TB2-dev1 <--> TB2-dev2 <---> TB1-dev <---> TB2-dev3

    in/out bound all the way out to TB2-dev2 is TB v2. TB1 device limits it and everything else downstream to TB v1 speeds.

Share This Page