Dynamic magnetic information storage or retrieval – General recording or reproducing – Signal switching
Reexamination Certificate
1998-09-08
2001-02-13
Faber, Alan T. (Department: 2753)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Signal switching
C360S076000, C360S075000, C360S069000, C360S061000, C360S062000, C360S077120, C360S251100, C360S261300, C360S291200
Reexamination Certificate
active
06188532
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to tape drives, and more particularly the present invention relates to a linear digital tape drive having a backward-compatible auxiliary head and head positioning assembly enabling read back of outdated standard tape formats.
BACKGROUND OF THE INVENTION
Magnetic tape is widely used for recording digital information. One extensive use of digital tape recording is to provide backup and archival storage of vast quantities of digital information, such as records comprising blocks of data. In some applications archival records are recorded on tape in a particular tape format which follows agreed standards at the time the recording was made. The tape may then be placed into archival storage and not retrieved until months or years have passed by. It is not uncommon to specify the useful storage life of recorded digital tapes and cartridges at thirty years, or longer. Whatever may be the useful life of a particular magnetic tapes, a primary assumption on the part of those who store such tapes away is that the recorded information may be read at some date in the future, if access to the archived data is required.
While a particular tape and cartridge may remain functional over many years after being in archival storage, tape transport mechanisms typically do not last nearly so long. Standardized tape recording formats are also susceptible to evolutionary changes and improvements. These changes are primarily driven by improvements in magnetic tape and magnetic head technologies which enable much larger data records and files to be stored on a given area of magnetic tape. One recent development, first employed in the hard disk drive industry, and more recently applied to tape recording, has been the introduction of head assemblies formed of thin film inductive, and magneto-resistive, and giant magneto-resistive (MR) read elements. These elements are typically fabricated in processes including photolithographic patterning steps of the type first developed for use by the semiconductor industry. One desirable aspect of these new thin film MR heads is that head gap widths may be narrowed considerably. Narrower head gaps and finer grain magnetic media coatings on tape mean that many more lineal data tracks may be defined across a magnetic recording tape of a standard given width (such as one-half inch tape). Also, the head structure may be formed as a single small composite structure on a common base or substrate and have as many as 12, or more, distinct heads. By using a common substrate, the heads may be formed to be in a predetermined precise alignment relative to nominal track locations defined along the magnetic tape. With e.g. 12 write and read head elements of the head structure in precise alignment with the defined nominal track locations, and with large scale integrated chips providing multiple data write/read channels, it has now become practical to have e.g. 12 channels for simultaneously writing user data to tape and for reading user data back from tape. This increase in the number of write/read channels effectively increases the overall data transfer rate between a host computer and the tape drive, and enables the tape drive to be characterized as having higher performance than previously available.
In order to take full advantage of the new thin film MR head technology in tape drives, a track layout which differs from previous standard track formats is required. This new track layout employs tracks of much narrower track width and pitch. Since the write/read heads are grouped together on a common fabrication substrate, the data tracks are also grouped together. In one arrangement, the data tracks are grouped into bands, or zones, across the tape, such that e.g. ten lateral head positions relative to the tape within a single zone would access 120 tracks. When a zone boundary is reached, the head structure or assembly is then displaced laterally relative to the tape travel path to the next zone, and the tracks of that zone then become accessible. Because track widths are very narrow, enabling track densities of e.g. 2000 tracks per inch, or higher, lateral tape motion must be followed in order to keep the new head assemblies in alignment with the tracks during tape travel past the head. Magnetic servo patterns written onto the tape may be read by servo readers and used to generate position error signals used by a closed loop positioner to correct head position. Alternatively, optical servo patterns embossed or otherwise formed on a back side of the tape may be used to provide position error signals, as disclosed for example in commonly assigned, copending U.S. patent application Ser. No. 09/046,723 filed on Mar. 24, 1998, and entitled: “Multi-Channel Magnetic Tape System Having Optical Tracking Servo”, the disclosure thereof being incorporated herein by reference.
The later high-density track format differs from previous standard formats. For example,
FIG. 1
shows an existing standard tape format employing longitudinal recording. In this example a magnetic recording tape
10
has a series of parallel longitudinal tracks. Three tracks
12
A,
12
B and
12
C are shown in the
FIG. 1
example, although more tracks, such as 24, 48, 96 or 128 tracks may be employed in a one-half inch tape lineal format in accordance with a particular standardized track layout plan. A head assembly
14
includes e.g. discrete inductive read or write head elements
14
A,
14
B and
14
C which are aligned with the tracks
12
A,
12
B and
12
C. Other tracks may be accessed by displacing the head assembly
14
laterally relative to the direction of the tape along a path indicated by the vertical arrows axial aligned with the head
14
in the
FIG. 1
view.
Another preexisting standard tape format employs azimuth recording of the data tracks, i.e. adjacent tracks are recorded with magnetic gaps oblique to each other, creating what appears generally as a “herringbone” pattern, shown in FIG.
2
. Therein, one track
16
A has its magnetic flux reversal pattern aligned with a first azimuth angle oblique to the tape travel direction, and an adjacent track
16
B has its magnetic flux reversal pattern aligned with a second azimuth angle in an opposite sense of the first angle relative to a travel path of the magnetic tape
10
. One known advantage derived from azimuth recording is that lineal guard bands or regions between tracks may be reduced, and the tracks may be placed closer together and read back without interference from adjacent tracks. While azimuth recording technology increases track density somewhat, complications arise in writing and reading the slanted tracks. Multi-element tape heads, such as the tape head
100
shown in
FIGS. 4-6
of U.S. Pat. No. 5,452,152, can be provided with some of the write/read elements having magnetic gaps aligned with one azimuth angle, and other write/read elements having magnetic gaps aligned with the other azimuth angle. Such heads are then positioned laterally relative to the direction of tape travel in order to come into alignment with particular tracks. An alternative approach, also shown in FIG.
2
and enabling compatibility with both the longitudinal tracks
12
A,
12
B and
12
C of the
FIG. 1
example, and the azimuth tracks
16
A and
16
B of the
FIG. 2
example, calls for rotating a head
19
having perpendicular head elements
19
A and
19
B between the two azimuth formats and the longitudinal format. One example of a multi-element head is given in commonly assigned, copending U.S. patent application Ser. No. 08/760,794 filed on Dec. 4, 1996, and entitled: “Four Channel Azimuth and Two Channel Non-Azimuth Read-After-Write Longitudinal Magnetic Head”, the disclosure thereof being incorporated herein by reference. An example of an azimuth tape recording pattern and an apparatus for writing the pattern in accordance with servo information read back from an adjacent track is given in commonly assigned U.S. Pat. No. 5,371,638, the disclosure thereof being incorporated by reference.
FIG. 3
illustrates a n
Albrecht Laurence J.
Saliba George A.
Faber Alan T.
Quantum Corporation
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