Why are HDD platters harder than the floppy/ZIP discs?

chuckcar wrote:
GreenXenon wrote in
:

Hi:

I have a question just out of curiosity.

I notice with ZIP discs and floppies, the disc is a soft dark-brown
round film-like material that can easily be shredded -- with paper-
shredder -- to remove confidential information.

However, the magnetic platters in HDDs are much harder and metallic.

Why don't they make the hard-disc-drive platters soft like the discs
of floppies and ZIPs? It would be so much easier to remove unwanted
confidential information then. Simply unscrew the HDD, remove the
soft platters and dump them into a paper-shreder.

To remove personal info from an HDD requires that the platters be
heated beyond Curie point to eliminate all magnetic data. This is
extremely inconvenient and dangerous because of the high temperatures
required.

Several reasons: 1. Rotation speed. Hard drives spin at several
thousand RPM (7,000-10,000), Floppies at under 500. You can actually
tell by their sound when a revolution is finished - less than a
second, but definitely discernable. 2. Head gap. Floppy disk heads
sit on the order of 1 mm from the surface of the disk and frequently
make contact with it.

In fact they always make contact and dont fly like a hard drive head does.

Hard drive heads float less than 10 millionths
of an inch over the surface and due to the speed involved will
destroy the surface if they contact it. However if you have to do
more than a full format, that's only the start of your security
concerns IMHO.

GreenXenon wrote:
On Jun 19, 1:28 pm, "Stephen" wrote:
This is down to several factors.

Typical hard drives are hermetically sealed units which allow the
platters to spin at a higher RPM than would be the case for Zip or
floppy drives.

If the hard disc was "floppy", you will find that it will distort if
you start spinning it at 5,400rpm (most laptop drives) or ar
7,200rpm (most desktop hard drives) or even at 10,000rpm (high
performance drives) the floppy media would probably tear itself to
shreds.

In addition, the gap between the read/write heads and the data
surface is very tiny, so any accidental bending of the disk surface
runs the risk of the heads destroying the data surface and making
the owner kiss goodbye to many Gigs worth of data. Having a
hermetically sealed disk means there is no issues with dust as there
would be on a removable disc.

In addition, if the hard disc surface was to increase in diameter
with the high rotational speed, the head positioning motors would
have to have a tracking compensation algorithm so it knew where the
data had "moved" to

So thats why hard discs have glass platters with a magnetic coating
on it.

zip discs and floppies spin at much lower rpm as the disk is not
hermetically sealed and to avoid disc distortion that would
otherwise occur at higher RPM and also are of lower data density
compared to todays HDD's og 500Gb to 1.5TB so head positioning on
zip and floppies os not as critical as it would be on a HDD.

Is it possible to hermetically-seal the soft disc of a floppy/zip?

Yes, and hard drives arent in fact hermetically sealed anyway.

Of course the spin speed would still have to be slow
to prevent the soft material from being injured. Right?

Nope. It would be possible to make flexible
material that could be spun at those speeds.

Is it also true that in order to have the same amount of storage
space, that the soft floppy material would need to be bigger in
diameter than the hard platter of an HDD?

Thats true in the sense that the bit densitys are much higher with rigid platters.

IOW, is it possible for a soft floppy disc to have
the same data density as a hard HDD platter?

Nope.

And its all completely pointless anyway when its so completely trivial to
use a decent security wipe like dban that completely wipes rigid platters.

The only thing it cant wipe is spared sectors.

GreenXenon wrote:
Hi:

I have a question just out of curiosity.

I notice with ZIP discs and floppies, the disc is a soft dark-brown
round film-like material that can easily be shredded -- with paper-
shredder -- to remove confidential information.

However, the magnetic platters in HDDs are much harder and metallic.

Why don't they make the hard-disc-drive platters soft like the discs
of floppies and ZIPs? It would be so much easier to remove unwanted
confidential information then. Simply unscrew the HDD, remove the soft
platters and dump them into a paper-shreder.

To remove personal info from an HDD requires that the platters be
heated beyond Curie point to eliminate all magnetic data. This is
extremely inconvenient and dangerous because of the high temperatures
required.


Thanks a bunch,

Green


Very simply, you couldn't make a flexible disk flat enough.

The recording density you can get is proportional to (among other
things) the gap between the head and the disk surface. To achieve a
very small gap HDD heads work on the principle of an air bearing, and
fly by ground-effect a tiny distance (tenths of a micro-metre) from the
surface. This requires that the surface be incredibly flat, the forces
on the head are tiny so the available acceleration to track surface
variations is also tiny. To achieve this the disk has to be very rigid,
very clean, and precisely machined.

When I worked in the business and learned about the "kissing track"
where the head hits the disk in order to find it, or lands on it when it
stops, I did the calculation of how long it would take the head to reach
flying height if it approached slow enough that ground effect would stop
it before it hit, I forget the answer now but it was huge, at least weeks.

They are sealed (and pressure equalised through a porous filter) to keep
out dust, Typical small dust particles are in the order of 10
micro-metres, boulder sized on the scale of the gap.

If you are worried about possible remnant magnetic data on a disk after
it has been wiped, you also ought to be worried about the remnant
footprints you leave walking down the street. They are about as easy
and reliable to trace.

What sort of criminal activity are you into that is worth spending
millions to try to dig out these tiny traces of fragmentary data and
bring them to a level of proof that would stand up in court, to
incriminate you? Especially as you could always argue that it was a
factory-refurbished machine and they were left by some previous owner,
or that such techniques have a significant chance of creating apparently
incriminating data from random noise. Should we even be talking to you
if you are that level of bad guy?


Tim Jackson

On Jun 19, 8:42*pm, GreenXenon wrote:
Hi:

I have a question just out of curiosity.

I notice with ZIP discs and floppies, the disc is a soft dark-brown
round film-like material that can easily be shredded -- with paper-
shredder -- to remove confidential information.

However, the magnetic platters in HDDs are much harder and metallic.

Why don't they make the hard-disc-drive platters soft like the discs
of floppies and ZIPs? It would be so much easier to remove unwanted
confidential information then. Simply unscrew the HDD, remove the soft
platters and dump them into a paper-shreder.

To remove personal info from an HDD requires that the platters be
heated beyond Curie point to eliminate all magnetic data. This is
extremely inconvenient and dangerous because of the high temperatures
required.

Thanks a bunch,

Green

Hey, GreenGlow, did you ever get answers to these questions yet?
What is Sphygmo-thermic dissociation?
When a neuron is stimulated, it depolarizes. When relaxed, it
hyperpolarizes?
They chased you from comp.dsp, sci.physics & sci.med.cardiology for
being a troll.
Grow up.....if you are ALLOWED, that is????

Tim Jackson wrote
GreenXenon wrote

I have a question just out of curiosity.

I notice with ZIP discs and floppies, the disc is a soft dark-brown
round film-like material that can easily be shredded -- with paper-
shredder -- to remove confidential information.

However, the magnetic platters in HDDs are much harder and metallic.

Why don't they make the hard-disc-drive platters soft like the discs
of floppies and ZIPs? It would be so much easier to remove unwanted
confidential information then. Simply unscrew the HDD, remove the
soft platters and dump them into a paper-shreder.

To remove personal info from an HDD requires that the platters be
heated beyond Curie point to eliminate all magnetic data. This is extremely inconvenient and dangerous because of the
high temperatures required.

Very simply, you couldn't make a flexible disk flat enough.

The recording density you can get is proportional to (among other
things) the gap between the head and the disk surface. To achieve a
very small gap HDD heads work on the principle of an air bearing, and
fly by ground-effect a tiny distance (tenths of a micro-metre) from
the surface. This requires that the surface be incredibly flat, the
forces on the head are tiny so the available acceleration to track
surface variations is also tiny. To achieve this the disk has to be
very rigid, very clean, and precisely machined.

When I worked in the business and learned about the "kissing track" where the head hits the disk in order to find it,

That was never the case with PC hard drives.

or lands on it when it stops,

That doesnt happen anymore either.

I did the calculation of how long it would take the head to reach flying height if it approached slow enough that
ground effect would stop it before it hit, I forget the answer now but it was huge, at least weeks.

Have fun explaining how hard drive heads fly then.

They are sealed (and pressure equalised through a porous filter) to keep out dust, Typical small dust particles are in
the order of 10 micro-metres, boulder sized on the scale of the gap.

If you are worried about possible remnant magnetic data on a disk after it has been wiped, you also ought to be
worried about the remnant footprints you leave walking down the street. They are about as easy and reliable to trace.

What sort of criminal activity are you into that is worth spending
millions to try to dig out these tiny traces of fragmentary data and bring them to a level of proof that would stand
up in court, to incriminate you? Especially as you could always argue that it was a factory-refurbished machine and
they were left by some previous owner, or that such techniques have a significant chance of creating apparently
incriminating data from random noise. Should we even be talking to you if you are that level of bad guy?

Rod Speed wrote:
Tim Jackson wrote

When I worked in the business and learned about the "kissing track" where the head hits the disk in order to find it,

That was never the case with PC hard drives.

or lands on it when it stops,

That doesnt happen anymore either.

I did the calculation of how long it would take the head to reach flying height if it approached slow enough that
ground effect would stop it before it hit, I forget the answer now but it was huge, at least weeks.

Have fun explaining how hard drive heads fly then.



AFAIK both Contact Stop/Start (CSS) and Loading/Unloading are still in
use on PC drives. Certainly both have been used on PCs, with
load/unload now being back in fashion, and I am not aware of any "third
way". If you have an alternative answer please share it, just
denigrating my answer does not help anyone.

As to how they fly, take off from a CSS landing zone is mechanically
straightforward, although a lot of research has gone into minimizing
wear during that process.

Loading unloaded heads is usually done by a static ramp that feeds the
head in close to the correct level to minimise the approach distance.
The mechanics of the situation require the slider to briefly kiss the
disk on approach, even if the manufacturers do not mention it, simply
because the unloaded detent position has to be many microns from the
surface to ensure separation. The ramp can't know where the disk
actually is to the necessary degree of accuracy, and ground-effect can't
give you the gees to decelerate the approach speed in time.

http://www.hitachigst.com/tech/techlib.nsf/techdocs/9076679E3EE4003E86256FAB005825FB/$file/LoadUnload_white_paper_FINAL.pdf

Tim Jackson wrote
Rod Speed wrote
Tim Jackson wrote

When I worked in the business and learned about the "kissing track" where the head hits the disk in order to find
it,

That was never the case with PC hard drives.

or lands on it when it stops,

That doesnt happen anymore either.

I did the calculation of how long it would take the head to reach flying height if it approached slow enough that
ground effect would stop it before it hit, I forget the answer now but it was huge, at least weeks.

Have fun explaining how hard drive heads fly then.

AFAIK both Contact Stop/Start (CSS) and Loading/Unloading are still in use on PC drives.

The heads are loaded and unloaded but they do not land on the platter anymore.

There was never ever any 'kissing track'. What we did see with stepper
motor head actuator drives was the heads moved against a physical
stop to recalibrate, but thats not a particular TRACK on the drive.

Certainly both have been used on PCs,

Nope, particularly that original claim about a TRACK.

with load/unload now being back in fashion,

Load and unload is an entirely separate matter to the heads
landing on the platters when the drive stops spinning. That
doesnt happen anymore, tho it did certainly happen at one
time. Thats what stiction is, the heads stuck to the platter.

and I am not aware of any "third way".

There is in the sense that the heads are retracted from the platters at shutdown.

If you have an alternative answer please share it,

I did, I told you that the first never happened, and
that heads no longer land on the platters anymore.

just denigrating my answer does not help anyone.

It does point out that your original is just plain wrong with current drives.

As to how they fly, take off from a CSS landing zone is mechanically straightforward, although a lot of research has
gone into minimizing wear during that process.

Waffle. It certainly doesnt take weeks.

Loading unloaded heads is usually done by a static ramp that feeds the head in close to the correct level to minimise
the approach distance. The mechanics of the situation require the slider to briefly kiss the disk on approach,

Like hell it does.

even if the manufacturers do not mention it,

They dont because it doesnt happen.

simply because the unloaded detent position has to be many microns from the surface to ensure separation. The ramp
can't know where the disk actually is to the necessary degree of accuracy,

The ramp is to retract the heads from the media so they no longer land on it anymore.

and ground-effect can't give you the gees to decelerate the approach speed in time.

Have fun explaining how real planes land.

http://www.hitachigst.com/tech/techlib.nsf/techdocs/9076679E3EE4003E86256FAB005825FB/$file/LoadUnload_white_paper_FINAL.pdf

That actually says that those drive DONT land the head on the platter when the drive stops, what I said.

And it does NOT say that the head touch the platter when they start flying either.

GreenXenon wrote:

I notice with ZIP discs and floppies, the disc is a soft dark-brown
round film-like material that can easily be shredded -- with paper-
shredder -- to remove confidential information.

However, the magnetic platters in HDDs are much harder and metallic.

Why don't they make the hard-disc-drive platters soft like the discs
of floppies and ZIPs? It would be so much easier to remove unwanted
confidential information then. Simply unscrew the HDD, remove the soft
platters and dump them into a paper-shreder.


A Major Difference between HDDs and Floppy Diskettes
( Or: Usually there's no need to worry about Magnets near an HDD)
http://mirror.href.com/thestarman/asm/mbr/DiskTerms.htm

Here's something I found of interest (same link):
"The platters of a common hard drive are not completely sealed off
from the outside as many people think. Therefore, you can damage an
HDD by running it at too high of an altitude where there is less air
pressure; since the heads may stay in contact with the platters or
skip up and down!" (the same force is involved or lacking due to air
pressure)

--

unfortunate ad placement, Mc Donalds
http://img95.imageshack.us/img95/442...dplacement.jpg

Rod Speed wrote:
Tim Jackson wrote
Rod Speed wrote
Tim Jackson wrote

When I worked in the business and learned about the "kissing track" where the head hits the disk in order to find
it,

That was never the case with PC hard drives.

or lands on it when it stops,

That doesnt happen anymore either.

I did the calculation of how long it would take the head to reach flying height if it approached slow enough that
ground effect would stop it before it hit, I forget the answer now but it was huge, at least weeks.

Have fun explaining how hard drive heads fly then.

AFAIK both Contact Stop/Start (CSS) and Loading/Unloading are still in use on PC drives.

The heads are loaded and unloaded but they do not land on the platter anymore.

There was never ever any 'kissing track'. What we did see with stepper
motor head actuator drives was the heads moved against a physical
stop to recalibrate, but thats not a particular TRACK on the drive.


Whatever you like to call it. It has nothing to do with head
calibration, it's the zone of the disk under the ramp where the heads
approach the disk and establish a stable flying height.

Certainly both have been used on PCs,

Nope, particularly that original claim about a TRACK.

with load/unload now being back in fashion,

Load and unload is an entirely separate matter to the heads
landing on the platters when the drive stops spinning. That
doesnt happen anymore, tho it did certainly happen at one
time. Thats what stiction is, the heads stuck to the platter.

and I am not aware of any "third way".

There is in the sense that the heads are retracted from the platters at shutdown.

That is load/unload.

If you have an alternative answer please share it,

I did, I told you that the first never happened, and
that heads no longer land on the platters anymore.

That's not an alternative explanation, it's just a denial. If I'm out
of date, I'm happy to learn. I admit it was the 1970's when I worked in
computer design, but I do try to keep up. But telling me it's no longer
done like that, it's now done by magic, doesn't help. I trained as a
physicist: I need mechanisms, and numbers that add up.


just denigrating my answer does not help anyone.

It does point out that your original is just plain wrong with current drives.

Not until you tell us how they get to descend from unload height to
flying height without touching the disk.


As to how they fly, take off from a CSS landing zone is mechanically straightforward, although a lot of research has
gone into minimizing wear during that process.

Waffle. It certainly doesnt take weeks.

Do the sums yourself then. How long does it take to get from say .001"
down to flying height, slow enough that ground effect stops you hitting
the disk.


Loading unloaded heads is usually done by a static ramp that feeds the head in close to the correct level to minimise
the approach distance. The mechanics of the situation require the slider to briefly kiss the disk on approach,
simply because the unloaded detent position has to be many microns from the surface to ensure separation. The ramp
can't know where the disk actually is to the necessary degree of accuracy,

The ramp is to retract the heads from the media so they no longer land on it anymore.

Sure. And when they come back off the ramp... ? How high above flying
height are they? How fast are they descending? How much time do they
have to stop in? How far *below* flying height must they get in order
to obtain a decelerative force to stop the descent in that time? Go do
the maths.


ground-effect can't give you the gees to decelerate the approach speed in time.

Have fun explaining how real planes land.

They use observation and/or instruments to predict the approach to the
ground and reduce their descent rate. If they don't know their relative
altitude they are rarely successful at landing on one piece. And they
don't fly at 1.5mm either, they fall many times that distance on landing.

Planes cannot land by ground effect alone. It would require an
impractically shallow angle of approach even to get to a flare height of
metres, never mind millimetres. And planes do touch the ground, they
don't go to level ground-effect flight.

I have yet to see a disk slider with elevator flaps, although maybe one
day...


http://www.hitachigst.com/tech/techlib.nsf/techdocs/9076679E3EE4003E86256FAB005825FB/$file/LoadUnload_white_paper_FINAL.pdf

That actually says that those drive DONT land the head on the platter when the drive stops, what I said.

And it does NOT say that the head touch the platter when they start flying either.


It says they all did until about 1995, which is over a decade of PCs,
and contradicts what you said. I agree it doesn't discuss the mechanism
of approach to flying height, I did say that.

Tim

Tim Jackson wrote
Rod Speed wrote
Tim Jackson wrote
Rod Speed wrote
Tim Jackson wrote

When I worked in the business and learned about the "kissing track" where the head hits the disk in order to find
it,

That was never the case with PC hard drives.

or lands on it when it stops,

That doesnt happen anymore either.

I did the calculation of how long it would take the head to reach
flying height if it approached slow enough that ground effect
would stop it before it hit, I forget the answer now but it was
huge, at least weeks.

Have fun explaining how hard drive heads fly then.

AFAIK both Contact Stop/Start (CSS) and Loading/Unloading are still in use on PC drives.

The heads are loaded and unloaded but they do not land on the platter anymore.

There was never ever any 'kissing track'. What we did see with stepper motor head actuator drives was the heads moved
against a physical
stop to recalibrate, but thats not a particular TRACK on the drive.

Whatever you like to call it. It has nothing to do with head
calibration, it's the zone of the disk under the ramp where the heads approach the disk and establish a stable flying
height.

Wrong. There was no ramp initially, that came later to avoid
stiction which happens due to the very smooth platter and head
and the heads never ever deliberately contact the platter anymore,
because the heads dont get anywhere hear the platter from the
ramp until the platters are up to rotation speed and so the last
thing you want is a head crash. They certainly dont ever
deliberately 'the head hits the disk in order to find it'.

That is utterly garbling what actually happens even with the original PC drives.

Certainly both have been used on PCs,

Nope, particularly that original claim about a TRACK.

with load/unload now being back in fashion,

Load and unload is an entirely separate matter to the heads
landing on the platters when the drive stops spinning. That
doesnt happen anymore, tho it did certainly happen at one
time. Thats what stiction is, the heads stuck to the platter.

and I am not aware of any "third way".

There is in the sense that the heads are retracted from the platters at shutdown.

That is load/unload.

Yes, but the heads never deliberately contact the
platter when there is a load/unload ramp in use.

If you have an alternative answer please share it,

I did, I told you that the first never happened, and
that heads no longer land on the platters anymore.

That's not an alternative explanation, it's just a denial.

You're lying now.

If I'm out of date, I'm happy to learn.

You clearly arent. You just try to bull**** your way out of your predicament instead.

I admit it was the 1970's when I worked in computer design, but I do try to keep up.

You need to try much harder.

But telling me it's no longer done like that, it's now done by magic, doesn't help.

I never ever said its dont by magic, liar. That cite you posted clearly states how the
load/unload ramp works and why the heads no longer contact the platters anymore.

I trained as a physicist: I need mechanisms,

That cite you post has the mechanisms, read it again.

and numbers that add up.

Then you will have to find those for yourself.

You dont need the numbers anyway when the heads only leave the
load/unload ramp when the platter is up to speed and the heads just
fly because the platter is up to speed when the head comes off the ramp.

just denigrating my answer does not help anyone.

It does point out that your original is just plain wrong with current drives.

Not until you tell us how they get to descend from unload height to
flying height without touching the disk.

That cite you posted does that, by waiting for the platters to come
up to speed before the heads are moved off the ramp over the platters.

As to how they fly, take off from a CSS landing zone is
mechanically straightforward, although a lot of research has gone into minimizing wear during that process.

Waffle. It certainly doesnt take weeks.

Do the sums yourself then.

No thanks. Its obvious to anyone with a clue that if the platters
are up to speed before the heads come off the ramp, they will
fly when they are designed to fly over the platters.

How long does it take to get from say .001" down to flying height, slow enough that ground effect stops you hitting
the disk.

Not even a second.

Loading unloaded heads is usually done by a static ramp that feeds
the head in close to the correct level to minimise the approach
distance. The mechanics of the situation require the slider to
briefly kiss the disk on approach, simply because the unloaded
detent position has to be many microns from the surface to ensure
separation. The ramp can't know where the disk actually is to the
necessary degree of accuracy,

The ramp is to retract the heads from the media so they no longer land on it anymore.

Sure. And when they come back off the ramp... ? How high above flying height are they? How fast are they descending?
How much time do they have to stop in?

Find that for yourself.

How far *below* flying height must they get in order to obtain a decelerative force to stop the descent in that time?

You dont know that they do ever get below flying height.

Go do the maths.

No need, whoever designed them did that and it clearly works fine.

ground-effect can't give you the gees to decelerate the approach speed in time.

Have fun explaining how real planes land.

They use observation and/or instruments to predict the approach to the ground and reduce their descent rate.

Wrong again. With light aircraft that have a significant ground effect, you
can close your eyes and use the ground effect to reduce the descent rate.

And dont try claiming it doesnt work like that, I've done it.

If they don't know their relative altitude they are rarely successful at landing on one piece.

Wrong, as always. Some like the F111 are effectively driven into the ground
and the undercarraige absorbs the remaining descent force. They dont flare.

Same thing happens with aircraft carriers, landing is more of a controlled
crash than anything else, there is no flare at all, essentially because there
isnt enough deck with an aircraft carrier and the last thing you want is flare.

And they don't fly at 1.5mm either, they fall many times that distance on landing.

Planes cannot land by ground effect alone.

Wrong, as always.

It would require an impractically shallow angle of approach even to get to a flare height of metres, never mind
millimetres.

Utterly mangled all over again. You just flare and use ground effect then.

And planes do touch the ground, they don't go to level ground-effect flight.

You can if you want to, and some have been designed to do that, usually over water.

I have yet to see a disk slider with elevator flaps, although maybe one day...

Flaps are there to increase the rate of descent and to change the attitude
when descending so you can see better. No need for them on hard drive heads.

And there is no such animal as 'elevator flaps' on a plane anyway.

http://www.hitachigst.com/tech/techlib.nsf/techdocs/9076679E3EE4003E86256FAB005825FB/$file/LoadUnload_white_paper_FINAL.pdf

That actually says that those drive DONT land the head on the platter when the drive stops, what I said.

And it does NOT say that the head touch the platter when they start flying either.

It says they all did until about 1995,

It ACTUALLY says that the START on the platter when the platter isnt rotating, a different thing entirely.

which is over a decade of PCs, and contradicts what you said.

Like hell it is.

I agree it doesn't discuss the mechanism of approach to flying height, I did say that.

And you mangled it completely.