Right now I think that the main advantage of S-ATA is cabling: thinner cables means better air-flow and easier placement of devices. It won't perform faster because of the interface alone. And because almost all optical drives are still P-ATA, I don't think that there is much to gain unless you can go to a full S-ATA system (Plextor does have a S-ATA DVD burner, but it's pricy!). But S-ATA is the future, so if you're planning a future system upgrade, then I would go for S-ATA, that my opinion
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Remember that when you install Windows XP on a S-ATA disk, you need a floppy with the driver to access the drive or else it won't find it.