Dynamic magnetic information storage or retrieval – Head – Head accessory
Reexamination Certificate
2001-06-07
2003-11-11
Heinz, A. J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Head accessory
C360S316000
Reexamination Certificate
active
06646830
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to read/write head arrays for magnetic data stores and more particularly to a monolithic magnetic read-while-write tape head.
2. Description of the Prior Art
Business, science and entertainment applications depend upon computers to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in gigabytes on 384 or more data tracks.
The improvement in magnetic medium data storage capacity arises in large part from improvements in the magnetic head assembly used for reading and writing data on the magnetic storage medium. A major improvement in transducer technology arrived with the magnetoresistive (MR) sensor originally developed by the IBM Corporation. The MR sensor transduces magnetic field changes in a MR stripe to resistance changes, which are processed to provide digital signals. Data storage density can be increased because a MR sensor offers signal levels much higher than those available from conventional inductive read heads for a given bit area. Moreover, the MR sensor output signal depends only on the instantaneous magnetic field intensity in the storage medium and is independent of relative sensor/medium velocity and the magnetic field time-rate-of-change.
The quantity of data stored on a magnetic tape may be increased by increasing the number of data tracks on the tape, which also decreases the distance between adjacent tracks. The width of the data tracks written by the read/write head assembly is limited by the width of the magnetic pole pieces in the write element but this track-width can be much narrower than the write element itself, which includes a write coil to energize the head gap. Present multi-channel tape recording systems achieve data track densities on the tape medium of twelve or more times the recording element density in the read/write head assembly.
In modem magnetic tape recorders adapted for computer data storage, the magnetic head assembly offers a read-while-write capability that is an essential feature for providing virtually error free magnetically stored data. Providing this bi-directional read-while-write capability usually requires fabrication and assembly of two or three separate modules. In the three-module approach, modules containing arrays of read heads are aligned with and assembled on both sides of a center module containing an array of write heads. Thus, for both directions of tape travel, the tape first passes over a center write-module to be written and then immediately passes over a closely-spaced read module for reading of the data just written. This approach requires independent finishing of the air-bearing surface (ABS) on each of the three modules and the precise assembly of the three modules into a single recording head. In the two module interleaved approach, two identical modules are fabricated, each containing an array of alternating read and write elements, starting with, say, a read element and ending with a write element. These modules are then assembled ‘face-to-face’ so that a read element always faces a write element. When the tape is moving one direction, half of the write elements are followed closely by a read element. When moving the other direction, the other half of the write elements are followed by read elements, thereby supporting bi-directional read-while-write operation providing immediate read back verification of the data written onto the tape medium. Alternatively, each module may contain “piggy-back” elements consisting of combined read and write elements such as used in direct access storage device (DASD) heads to increase data rates.
By continually reading “just recorded” data, the quality of the recorded data is verified while the original data is still available in the temporary storage of the recording system for reuse if needed. The recovered data is compared to the original data to afford opportunity for action, such as re-recording, to correct errors. Alternate columns (track-pairs) are thereby disposed to read-after-write in alternate directions of tape medium motion or in the other approach, all columns are written or read in parallel. Tape heads suitable for reading and writing on high-density tapes require precise alignment of the track-pair elements in the head assembly, as well as tight control of the skew of the head in the drive relative to the direction of tape travel. This latter requirement is eased by reducing the spacing between the read and write elements in each track-pair. Thus, higher-density data storage on tape requires tighter control of read and write element spacing tolerances along both the transverse and the track-line dimensions of the tape head.
FIG. 1
shows the air bearing surface (ABS) of a prior art embodiment of an interleaved magnetoresistive (MR) head assembly
10
, where the read elements are marked “R” and the write elements are marked “W”. The write elements, exemplified by the write head
12
and the read elements, exemplified by the read head
14
, are disposed in alternating fashion to form a single row of read/write track-pairs, exemplified by the R/W track-pair
12
-
14
. As used herein, the term “alternating” is intended to include other formats. For example, one format provides that the odd-numbered heads H
1
, H
3
, H
5
etc. are operative during forward tape movement, while the even-numbered heads H
2
, H
4
, H
6
etc. are operative during the opposite direction of tape movement. Generally, the length of the magnetic tape medium
16
moves in either a forward or reverse direction as indicated by the arrows
18
and
20
. Head assembly
10
is shown in
FIG. 1
as if magnetic tape medium
16
were transparent, although such tape medium normally is not transparent. Arrow
18
designates a forward movement of tape medium
16
and arrow
20
designates a reverse direction. Magnetic tape medium
16
and interleaved MR head assembly
10
operate in a transducing relationship in the manner well-known in the art.
Each of the head elements in head assembly
10
is intended to operate over a plurality of data tracks in magnetic tape medium
16
, as may be appreciated with reference to the data tracks T
1
, T
9
, T
17
, etc. in
FIG. 1
, which shows an exemplary 288-track scheme having a data track density on magnetic tape medium
16
of eight times the recording element density of R/W track-pairs H
1
, H
2
, . . . H
36
in MR head assembly
10
. Tracks T
9
, T
25
, . . . T
281
may be written with one pass of magnetic tape medium
16
in direction
18
over even-numbered R/W track-pairs H
2
, H
4
, . . . H
36
and then tracks T
1
, T
17
, . . . T
273
written on a return pass of magnetic tape medium
16
over the odd-numbered R/W track-pairs H
1
, H
3
, . . . H
35
by moving the lateral position of MR head assembly
10
in the direction of the arrow
21
by a distance equivalent to one track pitch (T
1
-T
2
), which is about 12% of the R/W track-pair spacing (H
1
-H
2
).
Interleaved MR head assembly
10
includes two thin-film modules
22
and
24
of generally identical construction. Modules
22
and
24
are joined together with an adhesive layer
25
to form a single physical unit, wherein the R/W track-pairs are aligned as precisely as possible in the direction of tape medium movement. Each module
22
,
24
includes one head-gap line
26
,
28
, respectively, where the individual R/W gaps in each module
26
,
28
are precisely located. Each thin-film
Biskeborn Robert Glenn
Eaton James Howard
Castro Angel
Heinz A. J.
Johnston Ervin F.
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