If you have ever opened a hard drive, you would noticed the disks are separated with rings but not attached to the spindle in any way.

What seems to happen is the disks and rings fly up and are pressed up against the end cap. I would assume this gives enough friction for the disk to be able to spin.

1. What causes the disks to fly up like that? Is it the Bernoulli principle? I do remember a hard drive called a Bernoulli box that used this method. It was basically a large floppy disk inside a sealed container.


2. How is the hard drive aware of the position of the disk? Is there some kind of magnetic signature that represents the home position?

 

If you have ever opened a hard drive, you would noticed the disks are separated with rings but not attached to the spindle in any way.

What seems to happen is the disks and rings fly up and are pressed up against the end cap. I would assume this gives enough friction for the disk to be able to spin.

1. What causes the disks to fly up like that? Is it the Bernoulli principle? I do remember a hard drive called a Bernoulli box that used this method. It was basically a large floppy disk inside a sealed container.


2. How is the hard drive aware of the position of the disk? Is there some kind of magnetic signature that represents the home position?

I'm not sure exactly what you mean in #1 above but I don't think that platters moves up or down on the spindle at all. I think that they are manufactured to fit the spindle precisely (without being connected to it) and with the separators, to spin without moving up or down which allows the heads to read and write.

https://www.explainthatstuff.com/harddrive.html


For #2, I believe that the location information is written with the low-level format.

http://www.active-undelete.com/hdd_basic.htm

I don't know what kind of kind of translation is used and I'm not even sure that newer technology can be low level formatted at all anymore. You may remember doing this to squeak out more life out of a failing drive.

In fact, I remember working on an old TRS-80 floppy and there was a Track 0 switch (which I replaced). The think would bang into it when it powered up and then then stepper motor (new HDD don't use those anymore either I guess) would click along and they held a ton and were lightening fast!! (well compared to a cassette tape).

Of course with SSD, in a few years someone else will be answering an analagous question, but recollecting the old days with voice coil HDD and low level formats.

Where is my rocking chair and slippers?? Hey you kids, get off my lawn!

 

But they aren't connected to the spindle in any way. Something has to keep them spinning. When you disassemble the drive the platters can be spun on the spindle without it moving. There must be friction involved after the motor starts.

 

Opened an old drive to check. The disk is firmly clamped to the spindle on it.

 

But they aren't connected to the spindle in any way. Something has to keep them spinning. When you disassemble the drive the platters can be spun on the spindle without it moving. There must be friction involved after the motor starts.

Oh, yes, now I understand, I was confused by your use of "fly up like that". Well, if it is not simple friction and centrifugal force, I don't know.

 

Opened an old drive to check. The disk is firmly clamped to the spindle on it.

Did they call you destructo as a kid?
I think that on at least some HDD the platters are definitely not connected to the spindle. Maybe it varies. Look at this teardown http://hddscan.com/doc/HDD_from_inside.html Seems like once he remove the spindle clamps, the platters lift off - no?

 

Did they call you destructo as a kid?
I think that on at least some HDD the platters are definitely not connected to the spindle. Maybe it varies. Look at this teardown http://hddscan.com/doc/HDD_from_inside.html Seems like once he remove the spindle clamps, the platters lift off - no?

The trick is being able to reassemble.

Sure they fall off once the top ring clamp screws are loosened but they are securely fastened to prevent up/down motion.

 

I have dozens of hard disk drives disassembled on my work bench. (I intend to remove the rare earth magnets).
I have never seen any disks not firmly clamped to the spindle.

 

I have dozens of hard disk drives disassembled on my work bench. (I intend to remove the rare earth magnets).
I have never seen any disks not firmly clamped to the spindle.

Have you ever seen any where the platters were actually attached to the spindle, or just firmly clamped?

 

Opened an old drive to check. The disk is firmly clamped to the spindle on it.

I have none handy that aren't torn apart. Are you saying it is actually just all clamped together?

The reason I mentioned they "flay up" is that the spacer sings will actually "fly up" then the spindle starts so that would rule out the Bernoulli principle on that one now that I think about it.
.

 

It seems unlikely platters would be a integrated part of the spindle due to the material processed needed to make the substrate and magnetic media uniform across the surface. Yes, they are firmly clamped to the spindle as any slippage or movement on metal to metal surfaces will cause particles at spin up/down and those particles would eventually hit the RW head destroying the drive.

 

It seems unlikely platters would be a integrated part of the spindle due to the material processed needed to make the substrate and magnetic media uniform across the surface. Yes, they are firmly clamped to the spindle as any slippage or movement on metal to metal surfaces will cause particles at spin up/down and those particles would eventually hit the RW head destroying the drive.

So no duct tape then?

 

It seems unlikely platters would be a integrated part of the spindle due to the material processed needed to make the substrate and magnetic media uniform across the surface. Yes, they are firmly clamped to the spindle as any slippage or movement on metal to metal surfaces will cause particles at spin up/down and those particles would eventually hit the RW head destroying the drive.

Are they clamped to the spindle? Or just clamped between the rings? Mine spun free with that top plate off. I think I have more up in the attic. I am going to try and get up there and grab one. I'll tear the cover off and see if I can spin the platters but not the spindle. But that will need to wait till tomorrow at least.

 

Considering the very high precision required in the head and platter location in modern hard drives, I'm quite sure that they are all firmly attached to the spindle when assembled.