anyone know the speed of the FW bus in dual G5s?

peaceful billypeaceful billy
Posted:
in Current Mac Hardware edited January 2014
hi



i'm trying to figure out the speed of the firewire bus in my dual 2Ghz G5.



i know that the apple docs list all three firewire ports as connecting to a Firewire PHY. but does anyone know the speed from that to the K2 controller?



i'd love to know how the Firewire PHY works, and if it does in fact have a total bandwidth to the K2 of 1600 Mbps.



does it suffer, like a PCI bus, from the 'whole bus gets set to the speed of the slowest component" thing - thereby turning a fw800 drive into a fw400 drive whenever a fw400 component is connected? i know i get conflicts between some firewire devices which go away if one of them is connected to a firewire port on a PCI card.



clearly, the three internal firewire ports go through this firewire PHY - but what is it and how does it operate? and why wouldn't apple just make each firewire port its own bus, like with the ATA drives?



anyone know or have any good ideas?

Comments

  • Reply 1 of 5
    altivec_2.0altivec_2.0 Posts: 995member
    If you have a FW 800 hard drive connected to the computer, and a FW400, both copying lets say a 3GB file. You will see a slight performance decrease. I don' think from the controller, mostly because of the slow speed of the Hard drive. That's really the only bottleneck in a system.
  • Reply 2 of 5
    g-newsg-news Posts: 1,107member
    the first firewire ports in the b&w G3s used to be called a "direct bus into the CPU at 100MHz".

    That of course is complete bollocks, but maybe they (a print magazine) meant to say 100MHz bus into the Northbridge.



    Then again, the G5 has FW 400 as well as FW 800, is about 4 years newer and has the FW ports connected to the southbridge...
  • Reply 3 of 5
    powerdocpowerdoc Posts: 8,123member
    Quote:

    Originally posted by peaceful billy

    hi



    i'm trying to figure out the speed of the firewire bus in my dual 2Ghz G5.



    i know that the apple docs list all three firewire ports as connecting to a Firewire PHY. but does anyone know the speed from that to the K2 controller?



    i'd love to know how the Firewire PHY works, and if it does in fact have a total bandwidth to the K2 of 1600 Mbps.



    does it suffer, like a PCI bus, from the 'whole bus gets set to the speed of the slowest component" thing - thereby turning a fw800 drive into a fw400 drive whenever a fw400 component is connected? i know i get conflicts between some firewire devices which go away if one of them is connected to a firewire port on a PCI card.



    clearly, the three internal firewire ports go through this firewire PHY - but what is it and how does it operate? and why wouldn't apple just make each firewire port its own bus, like with the ATA drives?



    anyone know or have any good ideas?



    from a pdf file :
    Quote:

    The Power Mac G5 architecture uses the HyperTransport protocol to integrate the I/O subsystems and connect them to the system controller. Serial ATA, Gigabit Ethernet, FireWire, USB 2.0, optical digital audio, and analog audio are all integrated through two bidirectional 800MHz HyperTransport interconnects for a maximum throughput of 1.6 GBps. For more information about the many expansion and I/O options available on the Power Mac G5, see the section ?Leading-Edge Expansion.? The Power Mac G5 with PCI-X slots provides bandwidth up to 2 GBps for PCI devices, eight times more than a Power Mac G4 and sixteen times more than a Pentium 4?based system.



    If my memory is correct it's implemented on 16 bits hypertransport.
  • Reply 4 of 5
    g-newsg-news Posts: 1,107member
    the southbridge is connected to the northbridge using 16 bits hypertransport, that is correct.

    however the firewire PHY is not connected to the southbridge using HT, it's some other connection and I think he's asking for that.
  • Reply 5 of 5
    peaceful billypeaceful billy Posts: 26member
    thanks for all the replies.



    yes, i am really curious about what the Firewire PHY is, how it operates, and - most specifically - what is the speed of its connection to the southbridge. i get that the K2 is connected to the PCI X bridge via HT.



    i haven't found any docs on the firewire PHY at apple. i've emailed apple about this, but haven't heard back.



    again, any info is most appreciated.



    thanks
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