FireWire 800 throttling down to 400 speeds: Say It Ain't So!

Discussion in 'Mac Pro' started by lPHONE, Dec 3, 2009.

  1. lPHONE macrumors 6502a


    Nov 17, 2009
    My friend told me that if I plugged an external drive into the 400 port that it would slow my other drive in my 800 port down to 400 speeds.


    (I have a Power Mac G5 Dual 2.3, if that makes a difference)
  2. spinnerlys Guest


    Sep 7, 2008
    forlod bygningen
    It isn't true.

    The FW400 port is independent from the FW800 port, otherwise it would make almost no sense to have two different ports for one bus.

    If you have FW400 device on the FW800 port, and a FW800 device connected to the FW400 device, you will only get FW400 speed for the FW800 device.
  3. iamcheerful macrumors 6502


    Oct 3, 2008
    Note: These situations may or may not be applicable to yours. My personal suggestion is to test it out yourself.

    If you prefer just to read a short version, this would be the only paragraph to read - unfortunately, yes, the speeds throttles down a significant amount. The long version follows ... (I'm trying to dig up an amazon user sharing his experiences with FW, will post a follow-up update when I get it.)

    Robert Mohns, FCP user, did some research on this issue specifically related to FCP ...

    The general consensus - generally on the same bus. If memory serves me correct, I have not heard/read a positive report yet.

    Other referring links:
    Link 1
    Link 2

    Update 1:
    The Amazon Link, a veteran mac user's experiences

    Update 2:
    Firewire BUS, Early 2008 Mac Pro, This is specific for the aforementioned Mac Pro, it may be similar to your Power Mac too.
    Apple's Documentation for Firewire states, "The PowerMac G5 computer has one FireWire 800 port based on IEEE 1394b and two FireWire 400 IEEE 1394a ports. The three FireWire ports are all on the same FireWire bus. They share a single power supply that can provide up to 15 watts total. The FireWire 800 port and the FireWire 400 ports provide a regulated power of approximately 25 VDC."
  4. rtrt, Dec 3, 2009
    Last edited: Aug 13, 2011
  5. mscriv macrumors 601


    Aug 14, 2008
    Dallas, Texas
    The Amazon review is quite interesting. I've not read or heard about other people having difficulties with Apple FW architecture. I've used daisy chained FW 400 drives on iMacs for the past several years and had no problems. The Amazon reviewer seems to indicate that there is a problem with FW 800 when used in this capacity. Does anyone else have any experience with this?
  6. iamcheerful macrumors 6502


    Oct 3, 2008
    rtrt, you were posting at the exact (well, almost exact) moment I was updating my post with more results. Thanks for helping out. I wouldn't have needed to dig that up if I knew you had it at hand ;)

    Here's another link to a user who tested out what happened when one introduces a mix setting.

    For what is worth ... here's another user supporting the fact that FW800 throttles to 400 ... This report (e-mail correspondence) is from Leica Users Group.

    I vaguely recall Rob from BareFeats doing a similar test years ago. If anyone knows of the link, do share. That said, my memory may be in question too. Forgive me k? ;)

    Just note one thing when/if you are going to perform your own experiment. Ensure that the hdd you are testing is capable of achieving 100 MB/s sustain large transfer (I'm ignoring burst speeds and random read/write since most of us use FW to work with large files) since that is the ceiling cap of FW800. Also good to note the chipset used.

    For me, I prefer practical real-life usage kind of test to synthetic benchmark testing.
  7. iamcheerful macrumors 6502


    Oct 3, 2008
    According to this ... in short - NO throttling of speeds as spinnerlys indicated

    This other thread shows no throttling of speeds.

    The post (near the end of the thread) by Article Accelerator (September 30, 2009 01:59PM) is very informative. I'll just do a compete quote here for reading conveniences for all ...
    (note: i have not verified the links working in the quote that follows)


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