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PCI Express Card Advice

by trupro / October 5, 2010 2:56 AM PDT

Hey folks, questions here about PCI express. Looking at these Combo cards out there with say, a couple FW800 ports and an eSata port (this would be exactly what I need).

Can these really run i/o at the same time, simultaniously moving data, or they are to be used one at a time (says 'onelane'. Common sense is telling me 'no' i suppose)

Not that I am settled on this one, but as an example:

thank you kindly for your input!
(btw: this is not a compatability question, but rather a theory question about typical PCI bussing architecture. I will take care of comapatablity...)

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by R. Proffitt Forum moderator / October 5, 2010 3:08 AM PDT

One lane would mean there is one lane. While it may look to the untrained eye that data is moving on both firewire and esata at the same time (which it would be!) that would be only a packet or buffer being transferred so if we get too Dilbert on it, it's not at the same time.

However does this matter? Have you tested that your application works or not?

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by trupro / October 5, 2010 3:13 AM PDT

its a combo USB/FW card. I guess Im really just asking if it is possible to have a card with a combo of eSATA and FW800, and use those ports for full duplex i/o, simultaniously (for instance, running an eSata external drive, while the card simultaniously runs an external audio interface) Thanks for your expertise!

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Again no.
by R. Proffitt Forum moderator / October 5, 2010 3:39 AM PDT

While the reason is simple, and the fact that a buffer could help the bottom line is whether the application and "system" would be fine with this is the acid test. No matter what way I look at this, the answer is no. With a single channel, only one or the other device is transferring data to the system at any one moment in time.

But that does not mean what you want to do won't work.

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Makes sense
by trupro / October 5, 2010 4:15 AM PDT
In reply to: Again no.

Ah, thank you much folks, these make sense.

I dunno why I kept typing PCIe...these are simply called ExpressCards, yes? My bad...

and indeed, it makes sense as you said to err on the side of caution. Alot of cards can do whatever you want but are truly putting it all through the same pipe as you said, so even if I could get it to work I'd be shooting myself in the foot as far as speed and functionality.

The idea is this: ive got one miniFW400. I then have an audio interface with FW400 connection, and an external drive with both FW400 ('mini' port...yuck!) and eSATA.

Since I only have one FW400 port in the lappy, im leaning toward just getting an eSATA card for the drive. Herein lies the conundrum: I want both on a better connection.

I'd like to get a firewire card, but then there is the problem you mentioned: a two port card (for both drive and interface) is essentially like daisy chaining through a single port. And thats not gonna work. Second is the fact that some laptops will route all FW bussing, card or no, through the same buss. So you could stick forty ports on there, its all gonna run through the same pipe.

I have yet to determine if my particular laptop manufacturer's architecture is this way, mostly because I dont speak the foreign languages of the helpdesks they have farmed all their customer support out to.

Any suggestions?

regardless, thanks again for your time and your expertise, much oblidged!

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For laptops.
by R. Proffitt Forum moderator / October 5, 2010 4:28 AM PDT
In reply to: Makes sense

All express cards are the same (I write this so someone can prove me wrong.)

But this does not mean that your application is limited or won't work. The reasons why are simple. We have buffers in the chips, the hard drive and what else so the data at the FW and eSata points may flow even when there is only a single channel on the other side.

And there's the conundrum. Do we go ahead and use it or do we dismiss it on a technicality?

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