Nvidia MCP79 SATA controller caps link speed 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.
Because devices connected are SATAI devices. How can you connect to a device at 3Gbps if it doesn't support it?