Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1998-05-22
2001-04-24
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06222698
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to recording and reading data to and from a data storage media, such as a magnetic tape, and more particularly to recording and reading data to and from a magnetic tape having tape dimensional instability.
DESCRIPTION OF THE RELATED ART
Magnetic tape data storage devices are widely used to backup data stored in non-removable disk drives in computers. Data stored in non-removable disk drives can be lost due to operator errors or mechanical failures. The cost per unit of stored data in a magnetic tape data storage device is low compared to other forms of electronic data storage. Therefore, the magnetic tape data storage devices provide a cost efficient means to backup data.
One method for storing data using a magnetic tape data storage device is known as “helical scan” technology. A magnetic tape data storage device using the helical scan technology records data in stripes that are diagonal relative to the length of a tape. In helical scan technology, a rotating drum head is used in conjunction with the tape that is slowly driven to yield high data storage capacity.
Another method for storing data using a magnetic tape data storage device is called “linear recording” technology. A magnetic tape data storage device using the linear recording technology records data in multiple parallel tracks that extend in the direction of the length of the tape. Unlike the helical scan technology, a stationary multi-transducer magnetic head is used in linear recording technology. With linear recording technology, the write and read transducers can simultaneously operate on a tape. In addition, the speed of the tape in a linear recording device is typically much greater than the speed of the tape in a helical scan device.
Referring to
FIG. 1
, a conventional configuration of a multi-transducer magnetic head
10
used in a linear recording device is shown. The multi-transducer magnetic head
10
is positioned over a portion of a magnetic tape
12
. The width of the magnetic tape
12
can be significantly wider than illustrated in FIG.
1
. The magnetic head
10
contains seven write transducers
14
and seven read transducers
16
. The write transducers
14
and the read transducers
16
form seven write/read pairs
18
, such that each write/read pair
18
contains one write transducer
14
and one read transducer
16
. Although the magnetic head
10
is shown to contain only seven write/read pairs
18
, other conventional configurations of magnetic heads exist with more or fewer write/read pairs.
A series of parallel data tracks
20
is shown on the magnetic tape
12
. Although only seven data tracks
20
are illustrated, additional data tracks could be located above and/or below the seven tracks. Between the data tracks
20
are track spaces
22
. The track spaces
22
are unaccessed regions on the magnetic tape
12
during a recording operation. The track spaces
22
correspond to the spaces between write transducers used for recording data into the data tracks
20
. Typically, the widths of track spaces
22
are substantially greater than the widths of data tracks
20
. The great disparity in widths of data tracks and track spaces is caused by spacing between write transducers on a magnetic head. Due to fabrication difficulties, the write transducers on a magnetic head are spaced much greater than the widths of data tracks. For example, the widths of data tracks
20
can be twenty microns wide, while the widths of track spaces
22
are 200 microns wide. The distance between the outermost data tracks
20
including the widths of the outermost data tracks (hereinafter “track span”) is W1.
As shown in
FIG. 1
, the lengths of the read transducers
16
are less than the lengths of the write transducers
14
. The difference in the lengths of the read transducers
16
and the write transducers
14
is to provide error margins on both side of the read transducer
16
to compensate for any age-related tape shrinkage, as well as other sources of track alignment errors. An error margin is the distance from an edge of a track
20
to the closest edge of a read transducer
16
on that track
20
.
Magnetic tapes such as tapes formed using a polyethylene terephthalate substrate tend to shrink over the useful life of the tape. The amount of shrinkage depends on several factors, such as temperature, humidity, material of the tape, and time. Age-related tape shrinkage can have a significant effect on the ability of a linear recording device to retrieve valuable data that was recorded onto a magnetic tape. Although age-related tape shrinkage may only involve a shrinkage of a few tenths of a percent in the width of a tape, the outermost read transducers on a magnetic head may be misaligned with the corresponding data tracks, especially if the magnetic head contains numerous write/read pairs. This is primarily due to the fact that track spaces are substantially wider than data tracks, such that a width of a single data track may only comprise about 1% of a track span. The proportion of a width of a single data track versus a track span decreases as more write/read pairs are fabricated on a magnetic head. A greater number of write/read pairs on a magnetic head equates to a higher data transfer rate.
FIG. 2
illustrates the potential effect of the age-related tape shrinkage when the age-related tape shrinkage is not sufficiently compensated by the error margins. In
FIG. 2
, the same multi-transducer magnetic head
10
and the same magnetic tape
12
that were shown in
FIG. 1
are illustrated. However, due to the age-related tape shrinkage, the length of the track span has decreased from W1 to W2. Because of the shrinkage of the magnetic tape
12
, the outermost read transducers
16
extend beyond the corresponding outermost data tracks
20
. Thus, the data recorded on the outermost data tracks
20
is not reliably read.
Servo tracking techniques have been developed to reduce the effects of read transducer-to-track alignment errors. Known servo tracking techniques vary widely, but most involve dynamically moving the magnetic head in the direction of the width of the tape to position the read transducers over the correct data tracks. However, such servo techniques are not necessarily effective in compensating for age-related shrinkage when used on conventional multi-transducer heads. Referring back to
FIG. 2
, the top read transducer
16
can be aligned with the top data track
20
if the magnetic head
10
is moved downward. However, the downward movement of the magnetic head
10
would further misalign the bottom read transducer
16
with the bottom data track
20
. Consequently, servo tracking techniques do not solve the adverse effects of age-related tape shrinkage in magnetic tapes.
One solution to the age-related tape shrinkage problem is to decrease the number of write/read pairs on a magnetic head. However, this solution will significantly lower the data transfer rate of the data storage device. In addition, sufficient error margins would still be needed to compensate for age-related tape shrinkage.
An effective method to alleviate the age-related tape shrinkage problem without affecting the data transfer rate is to increase the error margin by elongating the write transducers
14
. However, longer write transducers
14
will widen the data tracks
20
, causing fewer data tracks
20
to be recorded on the magnetic tape
12
. Because of demands for greater storage capacity of a magnetic tape used in a linear recording device, there is a desire to increase the density of tracks on the magnetic tape. Thus, an increase in the number of tracks on a magnetic tape is desired without changing the width of the tape. Although increasing the widths of the data tracks
20
is not the preferred solution, typical conventional linear recording devices have much longer write transducers compared to the read transducers to provide wider error margins. For example, the write transducers
14
could be twenty-seven microns long which would create twenty-seven micron data trac
Barndt Richard D.
Taussig Carl P.
Hewlett--Packard Company
Sniezek Andrew L.
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