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When I look at my Apple SSD TS256C (Toshiba) in the System Profiler on my MacBook Pro (Late 2011), I see:
Link Speed: 6 Gigabit
Negotiated Link Speed: 3 Gigabit
Why is that? Does that mean that the full 6 Gbit/s of SATA III aren't being utilized?
Strange coming from an OEM drive…
For my SuperDrive it's even lower:
Link Speed: 6 Gigabit
Negotiated Link Speed: 1.5 Gigabit
I have the low-end MBP 15'' early 2011.
It has a SATA3 interface. As I have a SSD build-in, the negotiated link speed is 6Gb/s as well. Benchmarks achieve speeds of up to 510 MB/s, which is clearly SATA3.
Also, make sure that you have the latest firmware installed. The early 2011 MBP received firmware updates which enabled full link speed (as of revision 2.2).
Because devices connected are SATAI devices. How can you connect to a device at 3Gbps if it doesn't support it?
Best Answer
Yes - at the moment - those link speeds are the theoretical maximum speed at which data can transfer to or from those devices.
The EFI firmware version on your MacBook Pro controls these link speeds as well as many other aspects of CPU throttling, so without reverse engineering that code - it's hard to know what or why the link may re-negotiate at a different speed. In the past, Apple has released EFI firmware updates to increase SATA link speeds for third party drives when they have done the engineering to make sure it will be stable enough - even if they don't support those drives. Of course they also release updates to improve their OEM parts in terms of speed and reliability so you can monitor those link speeds as well as your actual bottlenecks and submit bug reports if you feel things are not optimally configured - especially if you have some benchmarks or other data to show that case.