text/5/1
As you probably know, if you move a
magnet past a wire an electric
current is generated.  This is how
atomic generating stations work. 
An atomic pile turns water into
steam, the steam flows past fans,
making them turn.  The fans are
connected to magnets and the
magnets spin within coils of wire,
creating lots of electricity. This
is also how disks work.  Spots on
the disk are magnetized,
representing bits of bytes. As the
disk spins by a small coil in the
head, as the spots pass, spikes of
electricity are produced.  These
spikes are translated into bytes
and passed to the CPU and the RAM. 

~

text/340/3
    If you run a current through
a wire near a magnetizable
metal, the metal will become
magnetized. This is how writing
to a disk is done.  As the disk
turns past the coil in the head,
the coil is energized every time
an "on" bit is to be written to
the disk, resulting in a
magnetized spot. The switching on
and off of the electricity
flowing through the head is very
fast. 


~