What's the jumper "enable 1.5GB PHY" on a Western Digital hard disk?

What's the jumper "enable 1.5GB PHY" on a Western Digital hard disk? I've got a new hard disk. On the label there is a description of the jumper settings:
Asked by: Guest \| Views: 305

Total answers/comments: 2

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Guest [Entry]

"It's SATA II disk, right?

And if you put jumper on these pins HDDs will be SATA I.

It's there for if your motherboard doesn't support SATA II."

Guest [Entry]

"By jumping the two pins, 5 and 6, you limit the transfer rate to 1.5 GB/s.
PHY is simply the physical layer in question, between the drive and cables/transfer.
Take a look at Wikipedia's page on SATA throughput."