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Does motion sensor work for optical drive?

I just put a second hard drive in my macbook, in place of the optical drive :D

Was wondering if anyone here knows whether the Sudden Motion Sensor (SMS) will take care of that drive I have in the optical bay, or have I put that drive in danger??

The drive in my optical bay was the original HDD that came in the Macbook (when i bought it refurbished from CowBoom) then i put an SSD in its slot and moved it to the optical bay.

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The motion sensor is built into to the original drive and should still function as designed.

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The Sudden Motion Sensor (SMS) feature of the MacBooks is made possible by an accelerometer in the notebook itself that's connected directly to the motherboard. When triggered (by a given number of degrees rotation over a certain amount of time), the Mac issues a "park drive heads now" command that any notebook drive connected to the default SATA cable will obey, regardless of whether said drive features an accelerometer.

Many modern hard drives do ship with an integrated accelerometer to detect sudden motion and park the drive heads (and occasionally these drives cause system crashes / kernel panics resulting from the redundant engagement of both the drive-based and system-based motion protection features, which require the Sudden Motion Sensor (SMS) to be disabled via a Terminal command).

I ran my MacBook Pro 17-incher (Mid 2010) with an SSD in place of the hard drive with the original hard drive swapped into the optical bay, and I immediately noticed the absence of the distinct "click" noise of the drive safely disengaging when I moved the Mac, indicating that the optical drive SATA connection is outside the jurisdiction of SMS.

So, my advice would be to connect your rotational hard drive to the default cable, and run your SSD connected to the optical drive cable, which has equally fast throughput while allowing your more fragile, non-solid-state drive benefit from the SMS feature if there isn't an accelerometer in the drive itself.

There's some good info on Wikipedia.

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You are correct here! The sensor in the MacBook & MackBook Pro's is part of the logic board. You can buy HD's which have CrashGuard, so you could Replace your original Apple HD with a drive with CrashGuard and mount it to the optical drive port as well. Some MacBook optical drive ports are PATA not SATA so they will run slow. In these systems the Seagate SSHD hybrid drive maybe a better choice.


Definitely true for very legacy MacBooks (we're talking almost PowerPC old), but the optical and HD buses are identically fast on Mid-2010 onward Macbook Pros

EDIT: citing this Macrumors forum post for Mid 2010s having identical throughput on Optical and HD SATA buses



Sorry Noah, The ports are the same (SATA) but the logic to protect the drive from damage (Crash guard) is located within the logic boards of all but the newest retina systems and only on the HD drive bay. Here's an Apple T/N that talks about it: Mac notebooks: About the Sudden Motion Sensor


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