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Continually
increasing storage capacities in hard disk drives
require innovations in magnetic hard disk drive
design. One of the most unique and innovative
advances in hard disk drive design is a new
manufacturing technology for servowriting called
no-clock-head (NCH) servowriters. Using patented
servowrite self-timing technology, NCH servowriters
are key to a non-invasive servowriting process
that replaces the clock heads used in traditional
servowriting. As a result, performance, reliability,
and quality are much higher for hard disk drives
manufactured with this new process. NCH servowriters
have already been used successfully in the manufacture
of many Ultrastar* drives (such as the 9LZX,
18ZX, 18LZX, 36XP, and 36ZX) for both 7200 and
10,000 RPM speeds and a variety of capacities.
The
need for precision manufacturing
Hard disk drives store data in concentric tracks,
and the density of those tracks has increased
along with linear bit density over time. In
fact, the application of advanced read/write
elements has resulted in areal densities of
7.0 Gbits/sq. in. and track densities of 20,000
tracks per inch in Ultrastar server disk drives.
To
read and write data, the disk drive
head must remain accurately centered
on a selected track. At today's
track densities, the head must stay
centered on the narrow tracks to
within a staggering tolerance of
one-millionth of an inch. To achieve
this level of precision, the head
must read position information along
the track that is permanently written
onto the disk. The position information
is used by a precision electronics
control system that servos the recording
head onto the track.
Traditional
servo writing has been performed
in a clean room environment with
external sensors invading the head
disk assembly to provide the precise
angular and radial position information
to write the servo patterns. While
such instruments have been satisfactory
to set the patterns in the past,
today's increased track density
has become so precise that the mechanical
vibration of the file (relative
to these external sensors) can limit
the accuracy or increase the complexity
of these systems.
A
more precise servowriting technology
In
response to this need for greater precision
in hard disk drive servowriting, we have developed
a new manufacturing technology called no-clock-head
(NCH) servowriters, which use patented servowrite
self-timing technology. This new class of NCH
servowriters replaces the clock heads used in
traditional servowriters with an electronic
non-invasive process to create the nanosecond-
level time alignment of servo patterns between
adjacent tracks.
A
digital signal processor executing proprietary
mathematical algorithms is used to accomplish
this task. In this method, the hard disk drive
generates its own timing information while the
drive is being servo written, using only the
product data head. The patterns are self-propagated
and aligned by a digital signal processor (DSP),
resulting in a substantial increase in time
alignment over other servowriting methods used
in our products.
Figure
1. A disk drive with
an external clock head, typically
located on the disk outer diameter.
This provides the angular information
used to write the servo patterns
that are shown as pie-shaped sectors.
End-user data is stored in the larger
white regions between the pie-shaped
sectors.
Figure
2. Angular propagation
marks, generated by the data head
itself and used to create the precise
angular position of a clock head.
In this case, there is no clock
head.
A strategic technology for ongoing
improvements
Servowrite
self-timing technology is a breakthrough in
manufacturing technology and a first in the
disk drive industry. This new technology eliminates
pattern errorscaused by traditional external
sensors, improving data accuracy and drive performance.In
addition, the technology provides a pattern
accuracy designed to scale up with ever-increasing
areal densities-enabling even greater gains
in future products.
