assembly, a rail bracket assembly, and a magnet
The carriage is attached to the voice coil. The
carriage supports the head/arm assemblies and provides
the vehicle for head/arm positioning. The voice coil
moves the carriage in (extended) or out (retracted) as
determined by servo logic commands.
The rail bracket assembly provides a stable support
and guide for carriage movement. The carriage
bearings move along the upper and lower carriage rails
as the carriage is extended or retracted by the voice coil.
The magnet assembly is a very strong permanent
magnet that forms the core of the voice coil and is used
to mount components of the velocity transducer.
The velocity transducer helps to control the
acceleration and deceleration of the carriage assembly
during seek operations. The transducer coil has a
voltage induced in it by the motion of the transducer
core attached to the carriage. The voltage polarity and
amplitude are sensed by an operational amplifier and
used to indicate the direction and speed of carriage
assembly movement to the servo circuit logic.
There are six head/arm assemblies in each disk
drive. One of the head/arms holds the read-only servo
head. The other five assemblies hold read/write heads.
The servo head/arm assembly and two of the read/write
head/arm assemblies are upper surface head/arm
assemblies. The three remaining read/write head/arm
assemblies are lower surface head/arm assemblies.
The read/write heads are mounted on cam
controlled head load springs. As the head/arm
assemblies are loaded (extended) the head load springs
apply force (loading force) to the read/write heads to
move them toward the rapidly spinning disk surface
(3,100 rpm minimum). The air cushion above the
surface of the disk causes the head to float above the
recording surface. As the head assemblies are unloaded
(retracted), the head spring loading force is restrictedly
the cams and the heads are moved away from the
The servo circuit is a closed-loop servo system. It
is used to move the read/write heads to the desired
(addressed) cylinder when commanded by the
controller. The servo circuit is designed to maintain a
NULL or 0 voltage when the heads are in the correct
cylinder position. A position error signal is used to
indicate when the heads are not in the proper cylinder
location. The position error is fed to the voice coil and
results in carriage movement toward the addressed
cylinder. A feedback signal is developed using the
velocity transducer to oppose the position error and to
dampen carriage movement for smoother operation.
Track Servo Circuit
The track servo circuit is used for maintaining head
position over the track centerline. The track servo
circuit positions the read/write heads based on
information obtained from the servo tracks written on
the servo surface of the disk pack. The read-only servo
head reads the data written on the servo tracks and is
positioned accordingly. The read/write heads mounted
above (heads 0 and 1) and below (heads 2, 3, and 4) the
servo head are physically aligned to the servo head. By
positioning the servo head, all read/write heads are
positioned over the center of the correct track on their
respective recording surface of the cylinder.
The read/write circuits perform the following
When writing, they (1) convert serial NRZ
signals from the disk control logic to MFM data signals,
and (2) generate and control drive current to the write
heads for developing the flux fields used to store
information on the disk surface.
When reading, they (1) detect flux changes from
the disk, (2) convert the analog MFM signals to digital
MFM data, (3) convert MFM data to NRZ serial pulse
train and send it to the disk control logic, and (4)
generate the read clock signal.
DISK MEMORY SET OPERATIONS
The disk memory set receives data from the host
computer for storage on the disk and retrieves data from
the disk and transfers it to the computer. Because of the
relatively fast access time of the disk memory set, the
host computer uses the disk as temporary storage of data
as well as permanent storage of programs and data.
Before a disk can be used, it must first be formatted.