Re: How strong does a magnetic field have to be to affect a computer or a disk?

ANSWER TO QUESTION PROVIDED BY MICHAEL O. AYENI 

How strong of a magnetic field will it take to destroy the information 
on a hard disk or floppy disk?

This is a very good question and I will answer in segments so the 
information will be easy to understand. 

Definition: Floppy disks and hard disks can be called magnetic disks 
that are used to store information, data and programs for use on a 
computer. Information is converted in concentric tracks that are 
magnetically etched by a formatting program that arrives with the 
operating system

Why Magnetic Fields Affect Disks:
Magnetic charges on tapes or disks have to be spaced apart so that 
fields do not interfere with each other. The write head creates a 
strong magnetic field to reorient the magnetic molecules. The closer 
the read/write head is placed to the surface, the smaller the magnetic 
field needs to be. If data locations are too close, writing one bit will 
also affect its neighboring bits. Also, magnetized areas of a tape or 
disk that are too close will eventually change neighboring areas.

Unit and Strength of Magnetic Fields: 
The field strength of a magnet is measured in two ways, either in 
gauss (G) or tesla (T).  One tesla is equal to ten thousand gauss: 1T 
= 10,000G.  These criteria will use the Tesla scale as the basic for 
measuring the magnetic field strength of a magnet and the Gauss 
scale for measuring the extended distance of the magnetic field.  The 
magnet sizes currently being used in most routine clinical 
procedures vary in strength from 0.5T to 1.5T.  As a comparison of the 
strengths of these magnets, the earth's magnetic field strength is 
approximately 0.5G or 0.00005T at sea level in the mid-latitudes.

Tips on Disk Care:

1- Keep disks clean. Dirt, dust, hair, even the oil from fingerprints can 
build up to damage a disk.
 
2- Store disks out of the sun. A hot day can melt the plastic. 

3- Don't expose disks to extreme temperatures, either hot or cold. 
This can demagnetize a disk. 

4- Keep disks away from electromagnetic sources, like TVs, 
speakers, or power cords. 

5- Don't drop or beat on a disk. Sudden shocks can cause 
demagnetization



THE ANSWER TO YOUR FIRST QUESTION IS HERE!! In order for a 
magnetic field to affect a floppy disk it does not have to be 
considerably strong. A magnet on a refrigerator can destroy the 
information on a floppy disk. A magnet has to be of considerable 
strength to destroy the information on the hard drive of a computer. If 
you took the magnet of a 12 inch speaker (Sub-Woofer) and placed it 
next to your CPU, it (magnet from Sub-Woofer) will cause a 
considerable damage to your hard drive.

6- Make sure the speakers to your computer are shielded before 
placing them next to your CPU. 

7- Do not place a floppy disk next to a ringing phone. The phone 
generates a magnetic field when the ringer foes off which can distort 
the information on a floppy disk. 


Security Devices do not Affect Computer Equipment ; Disks included.
Security devices like you would find in Airports and Federal buildings 
use X-Rays which do NOT in any way interact with a magnetic field. 
An X-Ray has no way of disorienting a magnetic field so you have 
nothing to worry about when passing your computer or personal 
organizer through the X-Ray machine at an Airport or government 
building as far as I know.