Curious: how the "motion sensor" on iBook HD is rigged

[California]

I'm curious: how is the "motion sensor" on the iBook's hard drive rigged?

I've never seen the inside of the latest revision machines, but if there is something that actually protects the hard drives from a fall -- what is it? And does it make swapping out the hard drives more difficult? I know on regular iBooks and old pbs that it was just a plastic caddy and some screws with bumpers and the hd cable to the logic board.

What's the deal here? Yes, I'm thinking of doing a swap out with a better faster drive at non Apple pricing.

 

[mkrishnan]

Well...there are two things. There's the motion sensor. But the hard drive itself is just a normal hard drive. All hard drives can be commanded to "park" their read/write heads. A hard disk works by a magnetic probe/sensor floating over the disk as the disk spins. It can read the HD by reading the magnetic state of the block underneath it, and when a potential is applied, it can change the magnetic state.

Anyway, hard drives often get damaged because this head crashes into the disk and causes physical damage and/or misaligns itself. Parking essentially pulls the head out of the way so this can't happen as easily.

When the motion sensor detects the motion, the software or motherboard or whatever commands the disk to park, and it does. But the hard disk unit itself is identical to any other 2.5" hard disk, and it's mounted in the same way, AFAIK. So I think your answer with respect to difficulty of swapping is no.

 

[California]

Well...there are two things. There's the motion sensor. But the hard drive itself is just a normal hard drive. All hard drives can be commanded to "park" their read/write heads. A hard disk works by a magnetic probe/sensor floating over the disk as the disk spins. It can read the HD by reading the magnetic state of the block underneath it, and when a potential is applied, it can change the magnetic state.

Anyway, hard drives often get damaged because this head crashes into the disk and causes physical damage and/or misaligns itself. Parking essentially pulls the head out of the way so this can't happen as easily.

When the motion sensor detects the motion, the software or motherboard or whatever commands the disk to park, and it does. But the hard disk unit itself is identical to any other 2.5" hard disk, and it's mounted in the same way, AFAIK. So I think your answer with respect to difficulty of swapping is no.

Excellent answer. I didn't know it was a logic board command. That's very cool. I'm sure this is what happened recently on a trip with my newish 1.33 ibook's hd -- sold it under warranty and bought a motion sensor iBook. But not happy with the Fujistu hds I always seem to get.

 

[mkrishnan]

Yeah...it is a nice feature, and nicely implemented. IBM did it first in their Thinkpads, and Apple followed suit very shortly after. There's more info here:

http://www.kernelthread.com/software/ams/ams.html

I guess this motion sensor actually reports data on motion below the "critical threshold" to the OS. And people have used it to do funny things, sort of like the Kirby gamepack for the GBA -- where you can control things by twisting and tilting the powerbook.