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Right now I have a Hitachi 320GB 5400rpm and a MATSHITADVD-R UJ-868 superdrive connected to the Nvidia MCP79 SATA controller in my MacBook Pro 5,3. The link speed of the hard disk drive is negotiated to 1.5 Gbps as, according to this answer the device is a SATA I (1.5Gbps) device.
This is what my system profiler says about the SATA controller:

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

Now I'm wondering the following:

If I would replace the Hitachi HDD with an SSD of any brand will the negotiated link speed be 3Gbps? The SSD being a SATA II or III device. Or will this be capped because it has to divide the 3Gbps over the HDD/SSD and the Superdrive?

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There are two independent SATA channels available. Each channel will negotiate highest possible speed based on client capabilities. It will not divide 3Gbps between two clients.

And as a side answer to your question: in case you don't use Superdrive look for SATA to SATA 9.5mm optical bay caddy. This way you'll be able to put SSD in place of Superdrive and have plenty of storage on platters.

Your Macbook even accept 12.5mm thick HDDs in HDD chamber.

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So this guy ( is wrong? – Saaru Lindestøkke Jun 23 '12 at 15:06
Well he is as wrong as any other guy on the internet could be) You should read the whole discussion BTW -- – iskra Jun 23 '12 at 15:16
up vote 0 down vote accepted

I've replaced the Hitachi 320GB 5400rpm with a Seagate Momentus XT hybrid drive (4GB SSD + 500 GB HDD) and this is what it now says in my system profiler.

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

So this confirms what iskra is saying

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