There are two types of media used on hard disk platters: Oxide media
Thin film mediaOxide Media
Oxidemediais less popular on newer disk drives. A relatively soft material, it can be damaged
by a head crash should it be jostled while it is operating. Oxide media was very popular on
older low-end disk drive models because it was easily applied and inexpensive.
The primary ingredient in anoxide mediais iron oxide (a.k.a. rust). This media is applied
to the center of the platter in a syrupy liquid form. The disk is then spun at very high speed,
which causes the media to flow out to the edges of the disk, coating it evenly. After the liquid
media is cured, the disk is polished to even out its surface. It is extremely important that the
surface of the disk be smooth and free of bumps or blemishes, as will be discussed in the
section on read/write heads. Finally, a layer of material that protects and lubricates the sur-
face is added and polished smooth. Although it may sound like a lot of material is being
added to the disk, the thickness of the finished material is around 30 millionths of an inch.Thin Film Media
Virtually all disk drives manufactured today usethin film media, which is an extremely
thin layer of metals placed on the disk’s surface. The thin metal film is put on the disk as a
plating, like the chrome on your car, or by a process calledsputtering. Despite its unusual
name, sputtering is a very complicated way of plating a platter that electrically binds the
metal media to the disk in a vacuum. Thin film media is also calledplated mediaandsputtered
mediabecause of how it is applied to the disk. Sputtering is the method most commonly
used to place the recording media on disk platters.
Thin film media is harder and thinner than oxide media, and it allows stronger mag-
netic fields to be stored in smaller areas. All of which combine to allow higher density of
data and smaller disk sizes. Thin film is hard and if the disk is jostled during operation,
the read/write head just bounces off without damaging the media. It is extremely thin
and is very smooth, which allows the read/write heads to float closer over the media.Read/Write Heads
Each side of a disk platter has media applied to it that allows it to store data. Accordingly,
each side of a disk platter also has at least one read/write head, as illustrated in Figure 9-4.
As shown, a disk drive that has two disk platters has four read/write heads. There are ex-
ceptions to this rule, but generally a disk drive has two heads for each platter, one to read
and write data to the top side and one for the bottom side.
The read/write heads are all connected to the same actuator mechanism, as illus-
trated in Figure 9-4, which moves the heads in unison in and out, from the spindle to the
edge of the platter. Remember that the disk itself is spinning rapidly by. This means that
whentheread/writeheadforthetopplatter,usuallyreferredtoasdisk0,isovertrack29,Chapter 9: Hard Disks and Floppy Disks^175