THE 3.5-INCH FLOPPY DISK CON-
STRUCTION The 3.5-inch floppy disk is in a hard
plastic case. The media access hole is covered by a
metal spring loaded shutter. Write protection is
provided by a slide switch on the bottom of the case.
High density, 3.5-inch floppy disks have a media
indicator hole in the disk. A disk without this hole
cannot be formatted as a high density disk.
FLOPPY DISK DRIVE OPERATION Several
components are common to all floppy disk drives. The
spindle assembly/drive motor turns the disk at the
The drive circuit board controls the
reading and writing of data on the disk. Connectors and
cables connect the disk drive to the disk controller. The
read/write heads actually read data from a disk and write
data on a disk.
DENSITY AND COERCIVITY Density is the
term that describes how much data can be stored on a
disk. Coercivity is how much magnetic force,
measured in oersteds, is required to properly write data
on a disk. The density and coercivity of a disk is directly
related to the magnetic media of the disk.
USING LOW-DENSITY DISKS IN HIGH-
DENSITY DRIVES Avoid using low-density disks
in high-density drives, especially in 5.25-inch drives.
This is because of the difference in the size of the tracks
that high-density drives use. Never format a
low-density 5.25-inch disk as a high-density disk. The
3.5-inch disk drives do not have these problems because
the media indicator hole in the disk case prevents using
a low-density disk in a high-density format.
FLOPPY DISK DRIVE INSTALLATION AND
CONFIGURATION When installing a floppy disk,
you have to determine how the disk is to be configured.
You have to set the drive select jumper. Drive selection
is also dependent on the type of drive-to-controller
cable used. You must also determine the correct setting
for the terminating resistor, the diskette change
line/ready jumper, and the media sensor jumper.
FLOPPY DISK CARE AND HANDLING
Taking care of floppy disks will improve the reliability
of the data stored on the disk. It is important to be aware
of all potential sources of stray magnetic fields when
storing your disks.
DISK MEMORY SET The disk memory set is
also commonly referred to as a disk file unit or mass
memory storage unit. These devices have large
removable disk packs and are mainly for use with
MAGNETIC DISK PACKS Magnetic disk
packs are hard platters coated with a magnetic oxide.
They range is size from just 1 disk to over 14 disks.
Many disk packs have a servo surface that contains
permanently recorded data used for positioning the
DISK FILE UNIT CONTROLS AND IN-
DICATORS (DISK UNIT) The disk memory sets
controls and indicators allow the operator and
technician to set operating modes and monitor the
operation of the disk memory set.
DISK MEMORY SET CONTROLLER The
disk memory sets controller manages the operation of
the disk memory set. It has six main functional areas:
the controller intercommunications bus,
microprocessor, buffer memory, controller to disk drive
interface, the data bus control unit, and the CDS channel
DISK DRIVE UNIT The disk drive unit controls
the rotation of the disk pack, the positioning of the
read/write heads, and the reading and writing of data on
DISK MEMORY SET OPERATIONS Disk
memory set operations include disk formatting, write
operations, and read operations.
CARE AND HANDLING OF MAGNETIC
DISK PACKS Properly taking care of the disk packs
can prevent major head crashes and data loss.
FIXED HARD DISK SYSTEMS Fixed hard
disk systems are also commonly referred to as hard
disks. They are common in minicomputers and
FIXED HARD DISK DRIVE CONSTRUC-
TION Fixed hard drives consist of one or more disk
platters in a sealed head/drive assembly (HDA). The
HDA also contains the read/write heads and the head
actuator assembly. The head actuator assembly can be
a stepper motor or voice coil. It controls the movement
of the heads. The spindle motor is mounted outside of
the HDA. The spindle motor shaft penetrates the HDA
and turns the disk. The logic board of a fixed disk drive
controls the position of the heads and read/write
DATA ENCODING METHODS Methods for
encoding data on disks were developed to increase data
reliability and keep the controller synchronized with the
drive. The two most common encoding methods in use
are modified frequency modulation (MFM) and run
length limited (RLL).