Stephen wrote:

This is down to several factors.

Typical hard drives are hermetically sealed units

No they arent. They always have a filtered vent that allows pressure equalisation.

which allow the platters to spin at a higher RPM than would be the case for Zip or floppy drives.

It isnt the spin rate that allows the much higher bit density.

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

In fact hard drive heads fly. Floppy drives heads dont.

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

Nope, modern hard drives have embedded servo info that handles that
fine as the platter expand and contract due to changing temperatue.

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

They arent all glass.

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.

In fact the real reason is just the much higher bit densitys possible with rigid platters.


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.


Thanks a bunch,

Green