Apple Sudden Motion Sensor (SMS) confusion...

Hello all!

There seems to be a great deal of confusion when it comes to the Sudden Motion Sensor (SMS) in Mac laptops. SMS technology can be found in most modern Mac laptops. When sudden motion on any axis is detected, the laptop immediately parks the read/write heads of the hard disk drive. This is an attempt to safe guard the disk should the laptop be dropped or nudged sharply. However, it was not immediately clear to me whether the head parking technology in these machines would work with third party replacement drives, such as the blisteringly quick Seagate Momentus 7400.4 500GB.

I ordered one of the bad boys from OCUK above, expected the non-G version of the drive (the one without the built in motion sensor). I received my order from OCUK and discovered that they had actually sent out the G version, the one with a g-force sensor built in to the drive. I was a bit worried about whether the built in g-force sensor would conflict with the SMS in my unibody Macbook Pro after hearing some reports of Western Digital drives with motion sensors causing kernel panics.

Being my usual stupid self, I copied all my data over and whacked it straight into the machine without hesitation. So far, I have had no trouble with kernel panics or anything like that. Further more, the head parking technology in the Macbook Pro's still works, as a short jolt to the machine causes an increase in the load cycle count attribute in S.M.A.R.T. This attribute is associated with the head parking technology, as a head parking incident results in the load cycle count increasing by one.

So there you have it, the ST9500420ASG working flawlessly in my Macbook Pro late 2008 unibody, complete with head parking technology, and presumably the added 0G protection afforded by Seagate's own g-force sensor. I am getting really nice speeds out of the drive too, 100MB/sec in the theoretical tests. The OS feels a lot nippier, as expected when going from 5400 to 7200RPM.

The drive is almost as quiet as the stock drive, and the head parking noise is almost inaudible, requiring a very good ear to detect it. One word of caution tho, do not screw the hdd in too tight with the mounting bracket as this can lead to more vibration and hum in the chasis of the Macbook than is necessary. I recommend tightening the bracket so it is snug, but not mega tight.

Cheers

Jan