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Why is my SATA controller capping the link speed? This is what it says in my System Profiler under the Serial-ATA page:

Vendor:                 NVidia
Product:                MCP79 AHCI
Link Speed:             3 Gigabit
Negotiated Link Speed:  1.5 Gigabit
Description:            AHCI Version 1.20 Supported

The link speed is as expected (3 Gigabit), but I don't see why it is negotiated into a 1.5 Gigabit link speed.
The drives attached to the SATA interface are a Hitachi 320GB 5400rpm hard disk drive and a MATSHITADVD-R UJ-868 superdrive.

I have a MacBook Pro 5,3 with Snow Leopard 10.6.8. My question is why the negotiated link speed is lower than the actual link speed.

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up vote 1 down vote accepted

Because devices connected are SATAI devices. How can you connect to a device at 3Gbps if it doesn't support it?

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