PCI RAID card vs onboard RAID

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Just wondered what difference there would be in using a PCI RAID card (running 2 SATA drives in RAID 0) rather than the motherboards onboard RAID controller?

I would imagine using a RAID card might reduce the load on the CPU slightly, but would there be any significant changes to transfer rates?

Thanks for any replies

 

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Thanks for the reply.

I'd only be using SATA 1 drives (150MB/S) so I guess that the PCI bus would be able to handle this.

I wanted to go this way so I could connect a second RAID pair of disks and wondered if there would be any performance differences.