Re: How does the hard drive work?

Dear Jonathan:
     You have asked about the workings of hard drives, and how they can 
read the tiny bits of magnetic information when the drive head is so large.
The hard drive is a disk coated with magnetic iron oxide particles.  The 
disk spins continuously very fast in your computer and the head can travel 
in and out along a radius so that any location can be reached very quickly 
by the head. 
     Although the head may look large, actually the sensitive part of the 
head is defined by microlithographic methods so that the actual exposed 
portion of the head,which can either read or write the informaion on the 
disk,is very small-comparable to the dimensions of features on a 
microchip! As the manufacturing technology has improved over the years they 
have been able to shrink this area down to smaller and smaller sizes, and 
that is how the hard disk memories have risen to such large figures now.  
In addition they have increased the density of magnetic particles on the 
disk which makes the storage capacity larger.  For example in 1991 the 
density of storage memory was about 0.l3 Gbits/square inch.  In 1998 it was 
up to around 4 Gbits (30X the density!).  At the same time the lithography 
limit of the sensitive head area was about 4.5 uMeters in 1991, and in 1998 
was down to 0.5 uMeters, reduced by a factor of 9.   
     So that is how the storage density of the disks is now up to 30 GB or 
higher.  The information is stored in circular patterns on the disk and the 
location of the rings is measured by the computer and the spatial 
resolution is very high, so the location of the head to find data on the 
disk is exceedingly precise!

I hope this information satisfies your interest.  If you wish further 
informnation please contact me.   The information which is above comes from 
a magazine salled Solid State Technology, issue of September 1999, Page90.

R. Bersin...