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iMac 800 / 400 firewire imports

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peejack

macrumors 6502a
Original poster
Aug 7, 2007
700
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Could someone tell me if the 800 and 400 firewire ports on the new imacs share the same bus and if they would affect each others speed?

I have a firewire 400 soundcard/audio interface and just ordered a firewire 800 external drive, would they affect each other because i wanted them both for maximum performance.

Thanks

EDIT: I didn't mean 'imports' in the title just 'ports', sorry :)
 
I think the only way to slow down a FW800 device is to plug it into the FW400 port. I just checked and I have my FW400 drives plugged into my FR800 drives 400 port... I should perhaps just plug it into the iMac... in any event it all seems fast to me which is where the FW800 and TimeMachine come in...

PS... Just checked and in ports while not identified as 400 or 800 are certainly very different; I do not think it is possible to plug the wrong device into the wrong port.
 
vansouza said:
I think the only way to slow down a FW800 device is to plug it into the FW400 port. I just checked and I have my FW400 drives plugged into my FR800 drives 400 port... I should perhaps just plug it into the iMac... in any event it all seems fast to me which is where the FW800 and TimeMachine come in...

PS... Just checked and in ports while not identified as 400 or 800 are certainly very different; I do not think it is possible to plug the wrong device into the wrong port.
Click to expand...

Thanks for the reply, I mean will they slow down each other if they are both being used at the same time?
 
Yep thats how it works, if you have a FW800 hard drive plugged into the FW800 port, but then plug a FW400 device either into a port on the HD or a Firewire hub if you have it plugged into that, it will slow down all the devices on the FW800 port to 400 speed.
 
RevToTheRedline said:
Yep thats how it works, if you have a FW800 hard drive plugged into the FW800 port, but then plug a FW400 device either into a port on the HD or a Firewire hub if you have it plugged into that, it will slow down all the devices on the FW800 port to 400 speed.
Click to expand...


Sorry i don't understand full what you mean if i have both the 800 and 400 port on the back of the imac in use just with ONE piece of hardware (i.e the 800 a hard disk and the 400 a soundcard) the 800 speed will be affected?
 
He's asking if you use both the FW400 and FW800 simultaneously will there be any reduction in performance.
 
Must admit, it was always my impression that USB was very much shared, and that the limitation was if you have a load plugged in, you were limited to its max bandwidth across all devices.

Firewire I thought was different, in that you didnt share throughput across different ports. Even if on same bus, as the PCI-e connection (which alu imac uses) to southbridge would handle more than firewire can throughput.

This is opinion only, can't seem to find much on web to specifically answer your question.
 
RevToTheRedline said:
Yep thats how it works, if you have a FW800 hard drive plugged into the FW800 port, but then plug a FW400 device either into a port on the HD or a Firewire hub if you have it plugged into that, it will slow down all the devices on the FW800 port to 400 speed.
Click to expand...

Where did you get that, do you have a link?
 
peejack said:
Could someone tell me if the 800 and 400 firewire ports on the new imacs share the same bus and if they would affect each others speed?

I have a firewire 400 soundcard/audio interface and just ordered a firewire 800 external drive, would they affect each other because i wanted them both for maximum performance.

Thanks

EDIT: I didn't mean 'imports' in the title just 'ports', sorry :)
Click to expand...


I am almost certain they are on the same bus. Even the MacPro ports are on the same bus the last time I read about it. HOWEVER, a soundcard / audio interface has very low bandwidth usage, so it should not affect firewire 800 operation speed. Therefore, in this case, I am almost certain that they should both perform to maximum performance.
 
A look at the developer note for the iMac confirms that they are on the same controller. That suggests that while plugging in FW400 perpherial will not reduce the FW800 bus to 400 speeds, the same processor has to deal with requests from both and therefor may not provide as much overall bandwidth when heavy activity occurs on both ports. An example of this situation would be using a RAID via the 400 and 800 ports.

One interesting difference between the newest iMac and all other macs is that the FW controller is on a 1x PCIe bus, where older designs have the controller on a normal 33 mhz PCI bus. I would suspect that would make for better overall FW performance on the iMac, especally under heavy load conditions. Of course, that's assuming that the controller was bus transfer limited anyway, which in all honesty, I have no idea about. :)
 
Consultant said:
I am almost certain they are on the same bus. Even the MacPro ports are on the same bus the last time I read about it. HOWEVER, a soundcard / audio interface has very low bandwidth usage, so it should not affect firewire 800 operation speed. Therefore, in this case, I am almost certain that they should both perform to maximum performance.
Click to expand...


Great thanks, just waiting for it to turn up now to try/

Thanks for everyones help.
 
Consultant said:
Where did you get that, do you have a link?
Click to expand...

Other World Computing's Tech Rep told me

Obviously you will be fine if you use the FW400 port for 400 stuff and the FW800 port for 800 stuff, which I don't see why anyone wouldn't but I've been told by people higher up than me if you plug FW400 components into a FW800 port it will slow down the port to 400 speed. Including any faster device that's on that port.
 
Someone has reported to me that when using the firewire 800 hd with a firewire 400 audio interface when switch the hard drive on or in use it cuts out the audio :confused:
 
Does anyone fun a soundcard off firewire 400 and a harddrive off firewire 800?? Wanna know if it works or not before i get it.

Thanks very much.
 
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