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# DASD Capacity Enhancement by Varying Slider Skew

IP.com Disclosure Number: IPCOM000101679D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 81K

IBM

## Related People

Arnett, PC: AUTHOR [+3]

## Abstract

DASD devices suffer from the lack of an optimum areal density as the head is moved from one track to another. Typically, the data rate is kept constant, and the bit density must gradually decrease as the head is moved to the outer radius of the disk. In this case, the capacity of DASD systems can be written as: C = 2f x Ri x BPIo x (Ro - Ri) x TPI where BPIo is the number of bits per inch at the inner radius, TPI is the number of tracks per inch and Ri and Ro are the inner and outer radii of the stored information on the disk. Differentiating with respect to Ri and setting equal to zero to optimize the capacity, we find that we should set Ri = Ro/2 . The capacity is then exactly half of the case in which the areal density remains constant and the whole disk area is used.

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DASD Capacity Enhancement by Varying Slider Skew

DASD devices suffer from the lack of an optimum areal
density as the head is moved from one track to another. Typically,
the data rate is kept constant, and the bit density must gradually
decrease as the head is moved to the outer radius of the disk.  In
this case, the capacity of DASD systems can be written as:
C = 2f x Ri x BPIo x (Ro - Ri) x TPI
where BPIo is the number of bits per inch at the inner radius, TPI is
the number of tracks per inch and Ri and Ro are the inner and outer
radii of the stored information on the disk.  Differentiating with
respect to Ri and setting equal to zero to optimize the capacity, we
find that we should set Ri = Ro/2 .  The capacity is then exactly
half of the case in which the areal density remains constant and the
whole disk area is used.  The conclusions here are based on the
assumption that the data rate and TPI are to be held constant, as is
virtually always the case.  An alternative approach is to allow the
data rate (or the spindle speed) to change.  The latter solution is
too slow for hard disk operation, and the former has had some
commercial success by employing a few data bands with different data
rates, at some additional cost and interface inconvenience.  In
addition, there is a servo problem because the number of sectors must
be a function of the track radius, and in general the sectors will
not line up with each other across the tracks.

It is suggested that a single head can be made to offer a
continuous range of track widths by appropriate skewing with respect
to the tangential direction.  The skewing causes the head to have an
apparent track width which varies as the nominal track width times
the cosine of the skew angle, here denoted by r.  The skewing can be
performed as a part of the access mechanics of the drive
automatically. The principle advantage of the scheme is that the
storage will be constant density recording, and as such...