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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

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Theoretically, a 6 Gbit bus is faster than a 3 Gbit bus, but what good is a McLaren F1 (240 mph) on a US highway if it has to drive behind a Audi RS5 (175 mph). Are you saturating your bus at 3 Gbps? If the controller uses less power at lower speeds, wouldn't it make sense to negotiate a slower link speed until it's experiencing some amount of traffic close to the link speed limit before re-negotiating a higher link speed? – bmike Jan 4 '13 at 0:06
I do not believe that there is any optical disk drive in existence that can operate at a faster negotiated link speed than 1.5 Gigabit. I doubt that there is any drive that can actually reach that speed anyway. This is simply a limitation of the DVD and CD-ROM drive technology. – user9290 Jan 4 '13 at 0:10
@bmike, thanks, that makes sense. However, are you saying that if the bus is saturated, something in Lion will re-negotiate it to be 6 Gbps? – Baumr Jan 4 '13 at 13:32
The EFI changes many things based on environmental conditions and the Apple batter life is far better than equivalent PC hardware - so both of those point to Apple being more efficient with power. I don't actually know for sure on your model if it will re-negotiate, but there's a substantial doubt in my mind that it could if needed. We'd need to do more work on the chipset to see if it even has 6 Gbps so you may be right that it's a hard cap, too. Apple's several recent iMac lines do run at 6 Gbps - so there is a point where Apple decides it's worth doing today. – bmike Jan 4 '13 at 13:42
I would tend to assume the reporting of 6 is totally accurate, but even Apple does make mistakes from time to time. (sorry - too soon for a time joke about Apple - if it is, don't disturb me) – bmike Jan 4 '13 at 13:53
up vote 2 down vote accepted

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.

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The EFI Firmware of the mac controls the mobo's link speed, and is 'maxed' (current gen). The drive manufacturer, Toshiba, would have to release a firmware update for this specific drive's component combination to allow the drive to be faster, but only if all drive components can function properly at higher speeds. If you buy a car that can handle 104 octane fuel, you still need to buy it at the pump, otherwise you're operating at a lower level of performance than your car is capable. The car manufacturer didn't even fill it with 104 when you bought it! So, find a station that sells it! – NOTjust -- user4304 Apr 12 '13 at 20:18

In this case: The Toshiba TS256C is operating at its fastest factory designed speed. Basically, you bought an Apple computer with an SATA III (6Gbps) interface and an SATA II (3Gbps) Hard Drive, and an SATA I (1.5Gbps) optical drive. If you were to buy a different model of SSD or ODD that is SATA III rated for speed you could take advantage of the 6 Gbps speeds on either interface.

Apple has been known by the spec tracking community to do this for various models since around the time they introduced SSD's. It's a silly thing to do for a company that only officially supports a couple of after market internal hardware upgrades, basically limited to Crucial branded memory, AFAIK. Why they cripple their machines this way is probably a business decision: it's cheaper and most consumers won't ever know/figure it out/be able to tell.

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If this speed is fixed (and I don't actually know if it is) it could also be the result of exhaustive power/battery/performance tradeoffs as opposed to someone wanting to cripple a product. Everyone at Apple must be aware of each benchmark that will be run on each new product and that by juicing a link, they would show better - yet they persist in shipping well balanced systems IMO. – bmike Jan 4 '13 at 0:08

I have a mid-2012 (unibody, non-Retina) MacBook Pro 13" that I retrofitted with an OWC Mercury Electra 6G SSD, and my System Profiler reports

Link Speed: 6 Gigabit
Negotiated Link Speed: 6 Gigabit

So perhaps mine is faster than the OEM drive in your MacBook Pro.

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Thanks for the input. I think that OWC drives are, in general, faster than Apple OEM ones? Maybe the issue is that my OEM drive's SATA cable doesn't even support 6 Gigabit? – Baumr Jan 4 '13 at 17:28
There is benchmark software available for measuring the speed of an SSD in your particular system. Perhaps you could do a Google search looking for benchmarks and comparisons of different models.… – user9290 Jan 4 '13 at 17:54
Yes, that is correct. You have put a 6G drive into a computer with a 6G interface, therefore, you're all green for 6G link speed. – NOTjust -- user4304 Jan 4 '13 at 19:54

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