Hardware Reference
In-Depth Information
Oxide Media
The oxide medium is made of various compounds, containing iron oxide as the active in-
gredient. The magnetic layer is created on the disk by coating the aluminum platter with a
syrup containing iron-oxide particles. This syrup is spread across the disk by spinning the
platters at high speed; centrifugal force causes the material to flow from the center of the
platter to the outside, creating an even coating of the material on the platter. The surface
is then cured and polished. Finally, a layer of material that protects and lubricates the sur-
face is added and burnished smooth. The oxide coating is usually about 30 millionths of
an inch thick. Ifyoucould peer into a drive with oxide-coated platters, youwould see that
the platters are brownish or amber.
As drive density increases, the magnetic medium needs to be thinner and more perfectly
formed. The capabilities of oxide coatings have been exceeded by most higher-capacity
drives. Because the oxide medium is soft, disks that use it are subject to head-crash dam-
age if the drive is jolted during operation. Most older drives, especially those sold as low-
end models, use oxide media on the drive platters. Oxide media, which have been used
since 1955, remained popular because of their relatively low cost and ease of application.
Today, however, few if any drives use oxide media.
Thin-Film Media
Thin-film medium is aptly named. The coating is much thinner than can be achieved by
the oxide-coating method, but is much stronger. In fact, modern thin-film media are virtu-
ally uncrashable. Ifyoucould openadrive topeek at the platters, youwouldsee that plat-
ters coated with the thin-film medium look like mirrors. Thin-film media are also known
as
plated
or
sputtered media
because of the various processes that deposit the thin film on
the platters.
Thin-film plated media are manufactured by depositing the magnetic medium on the disk
withanelectroplating mechanism, inmuchthesame waythat chrome plating isdeposited
on the bumper of a car. The aluminum/magnesium or glass platter is immersed in a series
of chemical baths that coat the platter with several layers of metallic film. The magnetic
medium layer itself is a cobalt alloy about 1 μ-inch thick.
Thin-film sputtered media are created by first coating the aluminum platters with a layer
of nickel phosphorus and then applying the cobalt-alloy magnetic material in a continu-
ous vacuum-deposition process called
sputtering
. This process deposits magnetic layers
asthinas1μ-inchorlessonthedisk,inafashionsimilartothewaythatsiliconwafersare
coated with metallic films in the semiconductor industry. The same sputtering technique
isagainusedtolaydownanextremely hard,1μ-inchprotective carboncoating.Theneed
