Floppy disk drives are the simplest of all magnetic
disk devices, but contribute to a large number of
problems in personal computer operations. Most of the
floppy disk and drive problems you will encounter as a
technician are caused by improper system operation.
By thoroughly examining the operation of a floppy
drive, you can eliminate many of these errors. In the
following sections, we explore the construction of
5.25-inch and 3.5-inch disks and the operation of a
typical disk drive unit.
THE 5.25-INCH FLOPPY DISK
CONSTRUCTION
When you examine a 5.25-inch floppy disk, you
notice several holes and notches as well as the disk
itself. Figure 10-5 shows a 5.25-inch floppy disk.
The 5.25-Inch Disk
The disk is visible through the media access hole
on either side of the disk. The disk is made of thin
flexible polyester film that is coated with a magnetic
material. This material is iron-oxide on low-density
disks (360K) and cobalt on high-density disks.
Disk Jacket
The disk is enclosed in a plastic jacket to protect the
disk surface from contamination caused by dust, dirt,
and smoke. The inside of the disk jacket is lined with
soft felt to clean the disk as it spins. On the bottom of
the disk jacket are two notches called stress relief
notches. They help prevent the disk from warping and
relieve stress on the disk. Some drives also use these
Figure 10-5.—The 5.25-inch floppy disk.
notches to keep the disk in the proper position in the
drive.
Media Access Hole
Below the large hole in the middle of the disk is a
large oval hole called the media access hole. There is a
media access hole on each side of the disk. When you
insert the disk in a drive, the heads are positioned over
these holes to read or write on the disk.
Index Hole
Just to the right and above the media access hole is
a small round hole known as the index hole. If you were
to look at the disk, you would notice a small hole near
the big hole in the middle. This index hole indicates the
start of sector 1 on each track.
SOFT-SECTORED DISKS.— Soft-sectored
disks have only one index hole. The sectors are
physically written on the disk during the formatting
operation. The index hole indicates the starting point
for sector 1 on each track.
HARD-SECTORED DISKS.— Some disks have
eight or nine index holes. These are known as
hard-sectored disks and each hole represents the start of
a sector. Never try to use a hard-sectored disk in a drive
designed for soft-sectored disks as it will drive the
machine crazy trying to find sectors 2 through 9.
Write Enable Notch
On the right edge of the disk jacket, about 1 inch
from the top is a small notch in the jacket. This is the
write enable notch. In order to write on a disk, this
notch must be present. If you want to protect a disk from
accidental loss of data, cover this notch with a strip of
tape. Strips of tape for write protection are usually
provided in the box with the disks.
Central Hub Access Hole
In the center of the disk is a big hole known as the
central hub access hole. When you insert the disk in a
drive and close the door, a cone-shaped clamp centers
the disk and clamps it to the spindle motor. Due to the
pressure, many clamps exert on disks, most disks have
a reinforcement ring around the edge of the disk to
prevent damaging it.
10-7
