How can a PCI-Express x1 SATA controller card offer 6 SATA II slots?

This is a question regarding how the bandwidth works out. From what I understand, a single PCI-Express x1 has 2Gb/s of bandwidth. But a single SATA II slot uses 3Gb/s (please correct me if I'm wrong).

So how can an SATA controller card that uses PCI-E x1, offer multiple SATA II slots? For instance the SYBA SY-PEX40016 PCI-Express x1 SATA II has 6 SATA II slots.

So how does the math here work? And, if one for instance connected hard drives to the controller, would adding more drives make each drive slower?

Are the slots added by an SATA II controller card the same speed as the SATA II slots on the motherboard?
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  1. PCIE 2.0 is double that so PCIE 2.0 x1 is 4Gb/s of Bandwidth available which is more then enough to run a RAID array of conventional hard drives. Yes adding more drives will theoretically make it slower , but as long as the controller has a good command queue and the drives are fast enough it will barely be noticeable performance loss.
  2. OK thanks. I don't think the card I linked to was 2.0 though, I think it's just regular PCI-E x1.

    So if you have say 6 slots on the mobo vs. 6 slots on the controller card, then an array with 6 drives would be faster if it was connected via the mobo instead of the controller card? But, the difference would probably not be big?

    What about PCI (regular, not express) - what is the bandwidth of a regular PCI slot, and which controller card would be faster - a PCI one or a PCI-Express x1 one?
  3. Best answer
    The difference would be very minimal for mechanical hard disks RAID since they can rarely saturate even a PCI-E x1 slot, since a PCI-E 2.0 x1 is about 5x more bandwidth than the fastest mechanical hard disks can use.

    A single PCI slot provides 266MB/s which is also higher than what a mechanical hard disk needs, but if you intend to use more than 1 hard disk through the expansion slots a PCI-E slot would be recommended.
  4. Best answer selected by kadence.
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