Tape servo system and methods, write/read heads, and servo track configurations regarding same

A tape servo system includes tape having bands of tracks including at least one data band having a plurality of data tracks of track pitch P and a servo band dedicated for servo information. The servo band includes two or more noncontiguous servo tracks with each pair of adjacent servo tracks of the two or more noncontiguous servo tracks having a center to center separation equal to M*P, wherein M for each pair of adjacent servo tracks may be any integer .gtoreq.2. The system may further include a head assembly having a single magnetoresistive read element tapped to provide at least (K+1) tapped servo read elements for use in reading servo information written to the servo band; wherein K is equal to the integer M for the pair of adjacent servo tracks having the greatest center to center separation and a repositioning assembly for repositioning the head assembly as a function of the servo information. Further, the center to center separation between pairs of adjacent servo tracks of the two or more noncontiguous servo tracks may be different for at least two pairs of adjacent servo tracks. A servo tracking data recording tape with two or more noncontiguous servo tracks having center to center separation between pairs of adjacent servo tracks being different for at least two pairs of adjacent servo tracks is also provided along with a method for servo track identification for use therewith. Further, track read/write head assemblies wherein the servo read and write elements are along the same gap lines as the data read and write assemblies, respectively, are provided.

FIELD OF THE INVENTION 
The present invention relates to tape servo tracking. More particularly, 
the present invention relates to tape servo systems and methods, servo 
track configurations, and read/write heads utilized therewith. 
BACKGROUND OF THE INVENTION 
It is common to provide magnetic tape write/read head assemblies having one 
or more write/read transducer heads positioned transverse to the intended 
path of a magnetic recording medium, i.e., tape, for writing data on and 
reading data from parallel tracks on the tape. It is also known to include 
servo information on at least some of the tracks and provide servo 
transducer heads for reading such information to enable control of the 
lateral position of the head assembly, thereby dynamically maintaining the 
respective transducer heads of the head assembly relative to tape tracks. 
With the use of servo control, data track widths can be made significantly 
narrower and the capacity of the recording medium can therefore be 
increased. 
Various techniques for providing the servo information contained in tracks, 
i.e., servo tracks, have been previously employed. For example, it is 
known to provide dedicated servo tracks on the medium at the time of 
manufacture. However, it is desirable to enable an end-user to write a 
servo pattern on the medium in the field as opposed to factory writing of 
servo information. This allows the end-user to add the servo information 
to either a blank medium or utilize a medium which was either 
intentionally or unintentionally erased. 
There are a substantial number of different servo track configurations for 
providing servo control. For example, some of the different configurations 
are generally characterized by the utilization of either alternating 
information containing tracks embedded on an erased band and a single head 
or a center tapped head, as shown in FIG. 1, or alternating tracks with 
different distinguishable characteristics such as one or more discrete 
monofrequencies and a single head or a center tapped head, such as shown 
in FIG. 2. As shown in FIG. 1, a single servo transducer 14 is utilized 
for sensing servo information on the alternating servo tracks 12 in servo 
band 10 on an erased background for use in positioning data heads 19 
within the data bands 18. Alternatively, a center tapped head 16 may be 
utilized for providing position error signals as a function of the 
position of the head 16 over the tracks 12 within the servo band 10. 
As shown in FIG. 2, a single servo head 24 may be utilized for providing 
servo information from alternating servo tracks 22 within servo band 
having different distinguishable characteristics. The information is then 
used to position the data heads 29 correctly within the data bands 28 for 
performing read and/or write functions. Alternatively, a center tapped 
head (or two servo transducer elements) 26 may be utilized to generate a 
position error signal from the servo information recorded within the servo 
band 20. 
However, these different servo configurations have ambiguity associated 
with identifying which servo track is being used for deriving the position 
error signal to provide for servo control of the system. Although the 
servo track provides adequate positioning information, it does not provide 
any information as to which servo track the servo head is currently 
utilizing to generate the position error signal for servo control. 
Therefore, if the servo transducer is unintentionally repositioned, a 
misidentification of the servo track being used for servo positioning of 
the data read/write heads occurs. 
Various configurations attaining some improvement with respect to the above 
configurations are shown in FIGS. 3, 4, and 5, wherein multiple heads are 
utilized for generating positioning information from the servo information 
written in the servo band. As shown in FIG. 3, multiple heads 32 are 
utilized for reading servo information from a servo track 34 recorded in 
servo band 30 for positioning data heads 36 within the data bands 38. 
Further, as shown in FIG. 4, multiple servo heads 42 are utilized for 
reading servo information from a pair of distinguishable servo tracks 44 
within servo band 40 to position data heads 46 within data bands 48. 
The above configurations either rely on a single servo track utilizing 
multiple servo heads (wherein the number of heads is at least N-2 and N is 
the number of data tracks in a data band), rely on a pair of 
distinguishable servo tracks which also requires the use of at least N-2 
servo heads, or rely on a set of alternating distinguishable tracks which 
fill the servo bands. With the use of multiple heads and a single servo 
track or a pair of distinguishable servo tracks (FIGS. 3 and 4), an 
undesirable large number of servo heads is necessary. With regard to the 
latter multiple alternating distinguishable tracks, such tracks are very 
difficult to write in situ in a tape drive. 
For example, in writing multiple distinguishable tracks, servo write heads 
may not be placed adjacent to one another. Therefore, when servo tracks 
are written contiguous with one another as in the pair of alternating 
distinguishable servo tracks (FIG. 4) and set of multiple alternating 
distinguishable servo track (FIG. 2) configurations, it is required that 
they be written on multiple passes or with heads along multiple gap lines. 
For precision writing, this typically requires that the pattern be written 
in the factory. In many cases it is desirable to write servo information 
in the field. Further, although with the use of multiple alternating 
distinguishable tracks written across the servo band, the number of servo 
heads necessary is reduced to one or two heads, the problem of ambiguity 
in servo track identification is still applicable. 
In another servo configuration which utilizes multiple spaced heads as 
shown in FIG. 5 (extracted from U.S. Pat. No. 5,262,908, to Iwamatsu et 
al., issued Nov. 16, 1993), multiple heads 52 are utilized for reading 
information from a plurality of spaced servo tracks 54 within servo band 
50 for positioning data read/write heads 56 within data bands 58. However, 
with respect to such a configuration and the other configurations as 
described above which use multiple servo heads, it is difficult to produce 
head assemblies that include such multiple servo heads. Particularly, in 
thin film heads, limited space is allotted between adjacent data bands and 
therefore, space is limited for the leads from each of the multiple servo 
heads. In high track density heads, such leads are much larger than the 
width of the track pitch. As such, production of such multiple heads in 
the head assembly in such thin film heads is difficult. 
For the above reasons and other reasons that will be apparent from the 
description below, alternatives to the configurations such as those 
described above are needed to overcome difficulties associated therewith. 
For example, the unambiguous identification of individual servo tracks is 
desired. Further, it is desired to reduce the number of servo heads 
necessary for providing servo control and also it is desirable to write 
servo tracks in the field in a single pass. 
SUMMARY OF THE INVENTION 
A tape servo system in accordance with the present invention includes tape 
having a plurality of bands of tracks. The plurality of bands of tracks 
include at least one data band having a plurality of data tracks of track 
pitch P and a servo band dedicated for servo information. The servo band 
includes two or more noncontiguous servo tracks with each pair of adjacent 
servo tracks of the two or more noncontiguous servo tracks having a center 
to center separation equal to M*P, wherein M for each pair of adjacent 
servo tracks may be any integer .gtoreq.2. The system further includes a 
head assembly having a single magnetoresistive read element tapped to 
provide at least (K+1) tapped servo read elements for use in reading servo 
information written to the servo band; wherein K is equal to the integer M 
for the pair of adjacent servo tracks having the greatest center to center 
separation. A repositioning assembly of the system repositions the head 
assembly as a function of the servo information read from the servo band 
using the servo read elements. 
In one embodiment of the system, each data band includes N data tracks, the 
number of servo read elements is equal to H, the number of servo tracks is 
equal to S, and further S*(H-1).gtoreq.N. In another embodiment of the 
system, the center to center separation between pairs of adjacent servo 
tracks of the two or more noncontiguous servo tracks is different for at 
least two pairs of adjacent servo tracks. In yet another embodiment of the 
system, the head assembly includes a plurality of servo write elements for 
identically writing the plurality of servo tracks in a single pass; the 
servo write elements having the same gap line as the data write elements. 
Another tape servo system in accordance with the present invention includes 
tape having a plurality of bands of tracks. The plurality of bands of 
tracks include at least one data band having a plurality of data tracks of 
track pitch P and a servo band dedicated for servo information. The servo 
band includes two or more noncontiguous servo tracks with each pair of 
adjacent servo tracks of the two or more noncontiguous servo tracks having 
a center to center separation equal to M*P, wherein M is any integer 
.gtoreq.2. The center to center separation between pairs of adjacent servo 
tracks of the two or more noncontiguous servo tracks is different for at 
least two pairs of adjacent servo tracks. The system further includes a 
head assembly including a plurality of servo read elements (H) for use in 
reading servo information written to the servo band. The number of servo 
read elements (H) is equal to at least K+1, wherein K is the number of 
track pitches between the centers of the two servo tracks of a pair of 
adjacent servo tracks having the greatest center to center separation. A 
repositioning assembly of the system repositions the head assembly as a 
function of the servo information read from the servo band using the 
plurality of servo read elements. 
A servo tracking data recording tape in accordance with the present 
invention is also described. The tape includes at least one data band 
having a plurality of data tracks of track pitch P and a servo band 
dedicated for servo information. The servo band includes two or more 
noncontiguous servo tracks with each pair of adjacent servo tracks of the 
two or more noncontiguous servo tracks having a center to center 
separation equal to M*P, wherein M is any integer .gtoreq.2. The center to 
center separation between pairs of adjacent servo tracks of the two or 
more noncontiguous servo tracks is different for at least two pairs of 
adjacent servo tracks. 
In various embodiments of the systems and tape described above, the center 
to center separation between pairs of adjacent servo tracks is different 
for each pair of servo tracks across the servo band. Further, the 
separation between pairs of adjacent servo tracks may be different by one 
or more track pitches from one pair of servo tracks to a subsequent pair 
of servo tracks across the servo band, and yet further, the center to 
center separation between pairs of adjacent servo tracks may monotonically 
increase by one track pitch from one pair of servo tracks to a subsequent 
pair of servo tracks across the servo band. 
A system for writing servo track information within a servo band of a tape 
in accordance with the present invention is also described. The writing 
system includes tape including a plurality of bands of tracks. The 
plurality of bands of tracks include at least one data band having a 
plurality of data tracks of track pitch P and a servo band dedicated for 
servo information. The system further includes a head assembly including a 
plurality of data write elements and a servo writer having the same gap 
line as the plurality of data write elements. The servo writer writes two 
or more noncontiguous servo tracks in the servo band with each pair of 
adjacent servo tracks of the two or more noncontiguous servo tracks having 
center to center spacing equal to M*P, wherein M for each pair of adjacent 
servo tracks may be any integer .gtoreq.2. 
In one embodiment of the system, the head assembly further includes a servo 
erase head along another gap line for erasing the servo band. 
A method of servo track identification in accordance with the present 
invention includes spacing a plurality of noncontiguous servo tracks such 
that pairs of adjacent servo tracks have a center to center separation 
therebetween that is different for at least two pairs of adjacent servo 
tracks of the plurality of noncontiguous servo tracks. The method further 
includes sensing whether servo read elements of at least one pair of 
adjacent servo read elements are positioned proximate to the center of at 
least one of the servo tracks. 
In one embodiment of the method, the number of servo read elements is equal 
to at least K+1, wherein K is the number of track pitches between the 
centers of two servo tracks of a pair of adjacent servo tracks of the 
plurality of noncontiguous servo tracks having the greatest center to 
center separation. In another embodiment of the method, the method further 
includes comparing the sensed information to a predetermined algebraic 
code identifying each servo track. 
A method of reading servo information is also described. The method 
includes providing a tape including a plurality of bands of tracks. The 
plurality of bands of tracks include at least one data band having a 
plurality of data tracks of track pitch P and a servo band dedicated for 
servo information. The servo band includes two or more noncontiguous servo 
tracks with each pair of adjacent servo tracks of the two or more 
noncontiguous servo tracks having a center to center spacing equal to M*P, 
wherein M for each pair of adjacent servo tracks may be any integer 
.gtoreq.2. A tapped single magnetoresistive read element is positioned 
proximate the tape to provide K+1 tapped servo read element signals 
representative of K+1 servo read elements, wherein K is equal to an 
integer M of the pair of adjacent servo tracks having the greatest center 
to center separation. The method further includes cycling selectively 
through the K+1 tapped servo read element signals representative of the 
tapped servo read elements to provide a pair of outputs representative of 
the position of adjacent servo read elements of the tapped servo read 
elements relative to one or more of the noncontiguous servo tracks and 
comparing the pair of outputs to determine a position error signal as a 
function thereof. 
A head assembly in accordance with the present invention includes a 
plurality of data write elements along a first gap line, a plurality of 
data read elements along a second gap line, a single pass servo writer 
including servo write elements along the first gap line, and a single 
magnetoresistive servo read element tapped to provide a plurality of 
segmented servo read elements embedded between the plurality of data read 
elements along the second gap line. 
In one embodiment of the head assembly, the assembly further includes a 
servo erase element along a third gap line. 
Other head assemblies are also described including a head assembly having a 
plurality of data write elements along a write gap line and a single pass 
servo writer including servo write elements along the write gap line for 
writing two or more noncontiguous servo tracks. Yet another head assembly 
includes a single magnetoresistive read element and leads for tapping the 
single magnetoresistive read element at a spacing equal to a data track 
pitch with which the head assembly is utilized to provide at least three 
segmented servo read elements.

DETAILED DESCRIPTION OF THE EMBODIMENTS 
FIG. 6 schematically illustrates a closed loop tape servo system 60 for use 
in reading and writing to magnetic tape 64. The tape servo system 60 
includes a head assembly 62 positionable transversely relative to the 
length of tape 64 by positioning actuator 68. Servo information recorded 
in a servo band 76 of tape 64 is accessed utilizing head assembly 62 which 
includes a single tapped magnetoresistive read element 80 and multiple 
data read elements 82 along a common gap line 166, multiple servo write 
elements 102 and multiple data write elements 104 along a second common 
gap line 167, and a servo erase element 190 along a third gap line 168. 
The head assembly 62, is capable of writing servo track configurations in 
accordance with the present invention in a single pass. Further, the head 
assembly 62 provides signals representative of the position of the tapped 
servo read elements of the single tapped magnetoresistive read elements 80 
relative to servo tracks in servo band 76 to servo read circuitry 63 of 
position error signal generating circuitry 70. Servo read circuitry 63 
generates outputs representative of servo information in the servo band 
for use by processing unit or control logic 65 which generates a position 
error signal command based on the servo information from the servo read 
circuitry 63. 
The head assembly 62 is then positioned by positioning actuator 68 in 
response to a position error signal command conditioned by conditioning 
circuitry 67, such as an amplifier, to move the head assembly 62 such that 
alignment of the tapped servo read elements of the single magnetoresistive 
element 80 and servo tracks in the servo band 76 is achieved. Thereby, 
positioning of data read elements 82 and/or data write elements 104 are 
correctly positioned for reading and writing data to data tracks of 
individual data bands within the groups of data bands 72 of tape 64. 
Generally, the servo system 60 can employ servo write elements and servo 
read elements in the same gap lines as the data write and read elements, 
respectively. However, various concepts in accordance with the present 
invention are equally applicable to the use of multiple elements provided 
along separate gap lines, multiple elements provided by multiple spaced 
read elements as opposed to a tapped single magnetoresistive element, head 
assemblies including only servo read elements without servo write elements 
(i.e., the servo information written at the factory), head assemblies not 
including a servo erase element (i.e., field servo writing only possible 
on a pre-erased servo band), and various other head assemblies as would be 
readily apparent to one skilled in the art. 
As is described further below with reference to the alternate servo track 
configurations of FIGS. 14-16, the present invention contemplates the use 
of unique patterns of noncontiguous identical, i.e., monofrequency, servo 
tracks written on an erased servo band of the tape 64. More particularly, 
the unique patterns are provided with multiple spacing arrangements 
between the servo tracks. The unique patterns are selected in order to 
minimize servo track identification ambiguity and to minimize the number 
of servo read elements required to achieve servo control. 
As shown in FIG. 7, the tape 64 is divided into an integral number of 
groups of bands of tracks including groups of data bands 72. Within each 
group of data bands 72, each of the tracks is dedicated to a specific 
individual data band such as data band 74. One of the bands of tape 64, 
typically the center band, is dedicated for servo information and is shown 
in FIG. 7 as servo band 76. The servo band 76 is centered between the 
groups of data bands 72. However, it is not necessary for the servo band 
76 to be centered between the data bands as it could be positioned towards 
one edge of the tape or the other edge of the tape, or further could be 
positioned at one tape edge or the other tape edge. However, preferably 
the servo band 76 is centered to decrease tracking tolerances resulting 
from tape related track displacement due to, for example, tape contraction 
or expansion resulting from environmental change or ageing. The center 
positioning decreases the distance between the servo read elements 80 and 
the furthest most data elements 83 (FIG. 7). In each of the individual 
data bands 74, the data tracks are contiguous, e.g., the data tracks are 
directly adjacent one another. 
As shown in the more detailed view of the servo band 76 in FIG. 8A, servo 
band 76 includes two or more noncontiguous servo tracks, e.g., 
noncontiguous servo tracks being servo tracks which are physically 
separated by more than one-half track pitch P, in other words, are not 
directly adjacent to one another. Generally, in accordance with the 
present invention, the tape 64 includes a predetermined number of 
individual data bands 74 having a particular number of data tracks therein 
of track pitch P. Further, the tape 64 includes servo band 76 dedicated 
for the servo information with the servo band 76 including two or more 
noncontiguous servo tracks 78, such as identically written servo tracks 
85, 87, and 89. The center to center spacing between adjacent servo 
tracks, such as, for example, servo track 85 and servo track 87 as shown 
in FIG. 8A, is equal to M*P, wherein M may be any integer greater than or 
equal to 2. In the present invention, each servo track has a width that is 
equal to about the track pitch P. Preferably, the width is slightly 
greater than P, for example, 1.1P or less. As such, the width of the servo 
tracks need not be equivalent to the track pitch P. 
The head assembly 62 of servo system 60 for use in reading the servo 
information from the servo band 76 includes multiple servo read elements 
which can be configured as a single magnetoresistive element tapped at the 
data track pitch, as shall be described in further detail below. In 
general, with S being the number of servo tracks, N being the number of 
data tracks in an individual data band 74, H being the minimum number of 
servo read elements 80 necessary for reading the servo tracks 78 in 
accordance with the present invention, then the relationship between the 
number of servo tracks in the servo band 76 and the minimum number of 
servo read elements 80 is given by: S*(H-1).gtoreq.N. The minimum number 
(H) of servo read elements 80 in accordance with the present invention is 
equal to K+1, wherein K is equal to the integer M with M being the number 
of data track pitches between the centers of a pair of adjacent servo 
tracks, such as servo tracks 85 and 87 or tracks 87 and 89 (FIG. 8A). 
In the illustrative embodiment of the servo track and servo read element 
configuration, FIG. 8A shows the utilization of three noncontiguous servo 
tracks 85, 87, and 89. Each pair of servo tracks is separated by six data 
track pitches. For example, servo track pair 85 and 87 is separated center 
to center by six data track pitches and servo track pair 87 and 89 is 
separated center to center by six data track pitches. The configuration 
shown in FIG. 8A contains eighteen data tracks in an individual data band 
74 and therefore, in this particular illustrative embodiment, N=18, S=3, 
M=6, and H=at least 7. It should be readily apparent to one skilled in the 
art that such numbers may vary, including the number of data bands which 
could be either larger or smaller as generally shown by the above general 
equation. Further, although the servo band 76 is shown to be at the center 
of the groups of data bands 72 for minimizing the distance between the 
furthermost data head and the servo tracks, the position of the servo band 
76 may vary as previously described. Further, the tape 64 in this 
embodiment is generally known in the industry as quarter inch tape, 
however, the present invention is applicable to other available size 
tapes, such as 8 mm or 12.7 mm tape, or any other tape as would be 
generally known by those skilled in the art. 
FIG. 8A shows multiple servo read elements 80 in six different positions 
with respect to the tape 64. The six different positions are shown in a 
lateral direction for clarity even though head assembly 62 including the 
multiple servo read elements 80 are moved in a direction transverse to the 
length of tape 64 by positioning actuator 68. In the first position (left 
to right in FIG. 8), the two servo read elements at one end of the 
multiple servo read elements 80 access the center of the servo track 85 
and data element 82 accesses the first data track adjacent to the servo 
band 76. Likewise, in subsequent positions of the multiple servo read 
elements 80, various pairs of adjacent servo read elements of the multiple 
servo read elements 80 are positioned with respect to one of the 
noncontiguous servo tracks 85, 87, or 89 in order to position the data 
read element 82 to access the data tracks of the individual data bands 74. 
It is readily apparent that the data read element 82 may be either a read 
or write element depending upon the function to be provided by the drive 
and is not to be taken as limiting to the present invention. 
The servo tracks 78 are spaced such that each of the servo tracks 85, 87, 
and 89 provide for access of six different data tracks within the 
individual data band 74. As illustrated, servo read elements 80 utilize 
servo track 85 to access the first six data tracks adjacent to the servo 
band 76, servo track 87 is utilized to access the second six data tracks, 
and servo track 89 is utilized to access the last six data tracks of the 
individual data band 74. The servo tracks 78 are further separated from 
the data bands by servo guard band 84 to prevent the misinterpretation of 
information in adjacent individual data bands 74 as servo information. 
The method of reading and writing data on tape 64 in accordance with the 
present invention includes moving head assembly 62 in a direction 
transverse to the length of tape 64 to access one of the dedicated servo 
tracks 85, 87, 89 and thus the data track desired. The multiple servo read 
elements 80 are utilized to read the servo information identically written 
to the dedicated servo band to which the servo read elements 80 are 
proximate. The tape servo system 60 uses this servo information to 
determine the error between the position of head assembly 62 and the 
desired center position on one of the servo tracks 78. The position error 
information is then used to accurately position head assembly 62 utilizing 
positioning actuator 68. Therefore, data read/write elements are 
accurately positioned on the desired data tracks of the individual data 
bands 74 to which data can be written or from which data can be read. In 
general, data is written or read from the data tracks on tape 64 by moving 
head 62 approximately to the position where a pair of adjacent servo read 
elements of servo read elements 80 are positioned on the center of one of 
the servo tracks 78. With the utilization of adjacent servo read elements 
to sense the center location of the servo tracks, the width of the servo 
track can vary and the tolerances for the servo track dimensions can be 
loosened. This allows for such servo tracks to be more easily written in 
the field as opposed to higher tolerance writing of the servo tracks in 
the factory. 
By spacing the centers of the servo tracks 78 multiple track pitches apart, 
ambiguity of track location is reduced. In other words, the separation 
between the servo tracks 78 is of a distance great enough such that if the 
head slips off track by one or more tracks, such track slipping is 
acknowledged. As illustrated in the various positions of the servo read 
elements 80, only one pair of adjacent servo elements is allowed to access 
one of the servo tracks 78. In other words, the servo read elements 80 
become completely disengaged from one servo track, such as servo track 85, 
without picking up any adjacent signals from adjacent servo tracks, such 
as servo tracks 87 and 89. 
Further, with the use of noncontiguous servo tracks, the advantage of 
writing to the servo tracks on a single pass with a common servo writer, 
as further described below, can be utilized. In addition, the number of 
servo read elements is reduced or the number of taps of a single 
magnetoresistive element is reduced with the use of multiple servo tracks. 
Preferably, the servo tracks 78 are identically written such that they can 
be written in the field with a single pass. However, the present invention 
contemplates using different but similar densities to servo write each of 
the servo tracks in the servo band, such that track identification can be 
unambiguously determined. However, writing different densities would 
require such servo writing to be performed in a factory and not in situ, 
as there is insufficient room for three separate servo writers for writing 
the plurality of densities while still having the same gap line as the 
data write elements as further described below. 
One alternative to using different densities in order to unambiguously 
determine track identification is to use the same density on all tracks 
but use varied physical separation to determine which servo track is being 
accessed. Such variable physical separation to unambiguously determine 
track identification is further described below with reference to FIGS. 
14-16. 
An alternate configuration of the servo band and adjacent individual data 
bands is shown in and shall be described with reference to FIG. 8B. 
Additional dimensional characteristics in the separation of the servo 
tracks and data elements can be utilized such that guard bands or gaps 386 
can be used between multiple data tracks within the individual data track 
bands 374 along with the servo guard bands 384. Such use of gaps 386 
improves the tolerance to variations in servo track placement on the tape, 
i.e., such as, for example, variations that may occur due to tolerances of 
the write elements used to write the servo tracks. Further, the use of 
such gaps provides a band-edge guard band wherein alternate data bands can 
be written in opposite directions of tape motion without encountering 
additional tracking error, related to direction, between adjacent data 
tracks within the same data band. 
As shown in FIG. 8B, the two outer servo tracks 385 and 389 have an 
additional separation from the center of servo track 387 of dP1 which is 
less than or equal to the data track pitch P. Therefore, the center to 
center separation of adjacent servo tracks is equal to (dP1+M*P), wherein 
M is the integer number of data track pitches between the centers of the 
adjacent servo tracks. The value dP1 is also the width of guard band or 
gap 386 and the number of gaps or guard bands 386 in the individual data 
bands 374 are equal to S-1, for example, S-1=2 in FIG. 8B. Further, the 
separation from the center line of the group of servo read elements 380 to 
the centerline of the adjacent data head 382 is 
G+(S-1)*(M*P+dP1)+P*(H/2)! wherein G is the width of the servo guard band 
384. For example, as shown in FIG. 8B, where three servo tracks are used, 
the center to center separation from center servo track 387 to the outer 
servo track 385 is (6P+dP1), i.e., M equal to six. Further, the separation 
from the center line of the group of servo read elements 380 to the center 
of the adjacent data element 382 is G+(151/2*P)+(2*dP1). In addition, 
guard band 384 is provided such that if the servo read elements 380 move 
into the guard band region while active, a signal is not be picked up from 
the adjacent data bands. 
The multiple servo read elements 80 (FIG. 8A) of the head assembly 62 are 
preferably provided by a tapped single magnetoresistive element. However, 
multiple magnetoresistive elements may also be utilized in various 
configurations of the present invention. The single magnetoresistive 
element is tapped at the data track pitch across the single element as 
will be described further below with respect to several embodiments 
thereof. 
One layer of an illustrative embodiment of a read head structure in 
accordance with the present invention is shown in FIG. 9. The read layer 
90 of the head assembly 62 includes two groups of data read elements 92 
and a centralized seven element servo read section 94. As shown, the servo 
read section 94 includes leads 98 extending from a servo read element end 
portion 96 and terminating in termination pads 95. The leads of the data 
elements are shown in a folded configuration wherein one lead is folded 
over the other lead to reduce the space necessary for accommodating the 
leads. However, any lead structure is contemplated in accordance with the 
present invention and the present invention is in no manner limited by 
this configuration of the data elements and leads. 
The servo read element end portion 96 is shown in further detail in the 
alternative embodiments of FIGS. 10A and 10B. As shown in the illustration 
of FIG. 10A, the servo read element end portion 96 includes a single 
magnetoresistive element 116 which is tapped at the data track pitch by 
termination leads extending therefrom. As shown in FIG. 10A, such 
termination leads include termination tap leads 111 and input and output 
leads 110 and 112. The input and output leads, 110, 112 are utilized for 
connection to a bias voltage or current source and ground for biasing the 
elements. Between the outer leads 110 and 112 are six tap leads 111 
positioned at the data track pitch and insulated therebetween by an 
insulating material 113. The single magnetoresistive element 116 is tapped 
so as to provide signals representative of seven servo read element 
segments as required for use in the illustrative embodiment described with 
reference to FIG. 8A. It should be readily apparent that any number of 
tapped elements may be provided as determined by the desired servo 
configuration utilized. 
As shown in the alternate configuration of FIG. 10B, servo read end portion 
296 includes single magnetoresistive element 216 and further includes 
input and output segments 217, 219 fabricated of lead structure material. 
The input and output segment 217, 219 are aligned with the single 
magnetoresistive read element 216 to control the current flow through the 
single magnetoresistive material of the single read element. As such, 
current flows in a substantially linear fashion from the input lead 
segment 217 to the output lead segment 219 as opposed to the embodiment of 
FIG. 10A wherein current does not enter the single magnetoresistive 
element 116 in a linear fashion but rather at somewhat of an angle. By 
using the input and output lead segments of FIG. 10B, the current flows 
more uniformly from input to output and voltages provided by the tapped 
segments of the single element are more uniform when exposed to the same 
conditions. The end portion 296 also includes insulating layers 213 
isolating the leads 291, 210 and 212. 
Further, by having the servo read element segments contiguously adjacent to 
each other, adjacent segments operate as one half of a center tapped head. 
Such a configuration minimizes variation in the sensitivity between two 
distinct read elements due to fabrication tolerances. Further, such a 
tapped configuration allows for the minimization of signal amplitude 
variations due to variations in the head to tape placement. With both the 
configurations of FIGS. 10A and 10B, current flow through the termination 
leads 111, 291, respectively, is inhibited. 
The tapped single magnetoresistive element 116 provides outputs 
representative of the tapped element segments of the single element 116 to 
servo read circuitry 63. The servo read circuitry 63 of the tape servo 
system 60 for terminating or receiving outputs from the multiple servo 
read element segments is illustrated in FIG. 13. The servo read circuitry 
63 includes two banks 122, 124 of thin film amplifiers 128, 130, 
respectively. The outputs of the banks of amplifiers are connected to 
multiplexors 126 and 128 of the respective banks 122, 124. The amplifiers 
128 and 130 are utilized to provide selectable outputs via the 
multiplexors 126 and 128 from each tapped servo read element segment of 
the single magneto resistive element 116. By multiplexing the individual 
outputs and providing outputs from each of the banks 122, 124 
representative of adjacent servo read element segments, an error signal is 
generated by a comparison of the two outputs by differential amplifier 
142. 
The difference signal from the amplifier 142 is provided to signal 
processing unit 65 (FIG. 6), such as a digital signal processor, to 
provide for generation of a position error signal command to control 
positioning actuator 68 for movement of head assembly 62 transverse to the 
length of tape 64 for aligning the adjacent servo read element segments 
with the center of the servo track. The outputs are also summed by a 
summing amplifier 140 which may be utilized for providing automatic gain 
control. Further, a comparator 144 may be used for comparing one of the 
outputs to a reference or threshold to determine the transverse direction 
the head assembly 62 is moving relative to the tape 64. 
As shown in FIG. 13, one edge of tapped servo read element segment 116A is 
connected to amplifier 128A of bank 122. The other edge of tapped servo 
read element segment 116A, which is also at the edge of segment 116B, is 
also connected to amplifier 128A and, in addition, to amplifier 130B of 
bank 124. The other edge of tapped servo read element segment 116B is 
connected to one input of amplifier 128C of bank 122 and further connected 
to the other input of amplifier 130B of bank 124. The other tapped servo 
read element segments 116C-116G are connected in a similar fashion to 
respective amplifiers of the two banks 122, 124. It should be noted that 
the leads of each of the servo read element segments, except for the two 
outer tapped servo read element segments 116A and 116G, are each connected 
to an amplifier of each bank 122 and 124 such that signals representative 
of adjacent tapped servo read element segments 116 are provided to an 
amplifier in opposing banks. For example, signals representative of 
adjacent segments 116A and 116B are provided to bank 122 and bank 124, 
respectively. As such the outputs of the respective banks 122, 124 are 
representative when selected by the respective multiplexors of adjacent 
servo read element segments. The outputs can then be compared to provide a 
position error signal with respect to the position of a pair of adjacent 
servo read element segments relative to the center of a servo track. 
The operation of the servo system 60 shall now be described with reference 
to the tapped servo read element 116, representing the multiple servo read 
elements 80, being moved across the servo band shown in FIG. 8. As the 
head assembly 62 is moved transversely with respect to the length of tape 
64, servo read element segments 116A and 116B are moved across the first 
servo track 85. As servo element 116A is moved over the servo track 85, 
the signal upon preamplifier 128A is increased. With only servo read 
element 116A positioned on servo track 85, the difference value generated 
by differential amplifier 142 is representative of the fact that only 
servo read element 116A is positioned over servo track 85. As servo read 
element 116B begins to move over the servo track 85 and a portion of servo 
read element 116A is moved off of servo track 85, the selected outputs 
from the bank 122 and bank 124 representative of the adjacent segments 
116A and 116B get closer to being the same. The outputs of multiplexor 126 
and 128 are filtered and rectified by filters 128, 136 and rectifiers 134, 
138 and provided to differential amplifier 142. The differential amplifier 
142 compares the outputs, and as the difference between the two outputs 
approaches zero, the signal processing unit 65 determines that the servo 
track center has been found by the differential pair of sensors, i.e., the 
tapped servo read elements segments 116A and 116B. Therefore, the head 
assembly 62 achieves servo lock on servo track 85. Thereafter, data 
read/write element 82 can then be utilized to read or write data to or 
from the first track adjacent the servo band 76. It should be noted that 
the number of data elements for reading and writing are numerous as shown 
in FIG. 7 and the head assembly of FIG. 6. 
Not shown in FIG. 13 is an AC coupling capacitor or a compensation circuit 
in the preamplifiers required to manage the large voltage drop across each 
servo read element segment relative to the signal provided to the 
preamplifiers. For example, the signal of the tapped servo read element 
segment may be typically, for example, 1 to 3 percent of the DC voltage 
across the entire single magnetoresistive element. 
It should be readily apparent that the concept of odd/even banks of 
amplifiers selectable to provide outputs for difference comparison 
utilizing tapped servo read elements may include any number of servo read 
element segments and any number of amplifiers depending upon the servo 
configuration utilized. The illustrative embodiment of FIG. 13 provides 
for the termination of the seven servo read element segments as utilized 
in conjunction with the servo configuration shown in FIG. 8A and 8B. 
However, the present invention is in no manner limited to this particular 
illustrative embodiment, but is limited only as described in the 
accompanying claims. 
Although the servo tracks of the various configurations may be written at 
the factory, it is preferable that the head assembly 62 include a servo 
writer 102 for writing the servo tracks in the field, i.e., in situ. Servo 
writer 102 in accordance with the present invention as shown in the 
illustrative drawing of the head assembly 62 in FIG. 6, is embedded in the 
data write elements 104 as shown in FIG. 11 along a common gap line 167 
(FIG. 6). FIG. 11 is an illustration of a data write layer 100 of the head 
assembly which shows multiple data write elements 104 with the servo 
writer 102 centered between two groups of the data write elements 104. The 
servo writer 102 is offset 1/2 of the data track pitch from the data write 
elements such that the servo tracks are positioned for the servo read 
elements to read and properly align the data elements on the data tracks 
when centered. 
The head assembly 62 is a thin film head and the servo writer 102 includes 
a thin film servo write comb structure 106, shown in further detail in 
FIG. 12 along with further detail of two adjacent data write elements 104. 
The servo writer further includes termination leads 108 extending 
therefrom. 
As shown in FIG. 12, the comb structure 106 is for use in writing 
noncontiguous servo tracks in a single pass of the tape 64. The servo 
writer 102 is positioned in the center of the data elements 104 to 
minimize the separation of the outermost data elements from the servo band 
76, although other positions of the servo band may be utilized. The data 
write elements 104 are uniformly separated by an integer number of data 
track pitches unless guard bands are utilized as shown in FIG. 8B. 
The thin film servo writer 102 includes a common bottom pole 166, a 
continuous set of coils arranged in one or more layers 168, and a top pole 
172 with two or more teeth or fingers separated for writing the servo 
tracks as desired for the various servo configurations described herein. A 
back closure 170 to the bottom pole 166 is also provided. Further, as 
shown in FIG. 12, the top pole 172 is recessed from the tape bearing 
surface by several microns to prevent recording in the region between the 
teeth where writing of servo information is undesired. With a common coil 
for the various teeth, identical servo tracks are written. As the servo 
tracks are written at the same time and each of the teeth have a common 
gap line, parallelism, and/or collinear transition, between the tracks is 
easily maintained. 
The comb structure, as shown in FIG. 12, reflects a three finger or tooth 
comb such as utilized in writing the servo tracks as illustrated in FIG. 
8A. The servo writer 102 occupies approximately the width of an individual 
data band 74. Further, the teeth of the comb-like structure 106 forming 
the individual write poles have a common planar gap line 167 (FIG. 6) 
which is the same as the data write elements 104. In an initial pass of 
the tape 64 across the head assembly 62, the servo information can be 
written to a pre-erased servo band. Typically, this is only performed 
once. Subsequently, all data writes or reads are made while the head 
assembly 62 is being servo controlled. This obviates the need for factory 
servo writing capability. If the servo information is inadvertently 
damaged, it can be rewritten by the drive using the servo writer 102. 
The servo writer 102 is embedded between the data write elements with the 
use of common thin film processing steps. For example, with formation of 
the servo writer, common processing steps for forming both the top poles 
of the servo writer 102 and the top poles of the data write elements 104 
are used. The steps of the thin film process for forming both types of 
write elements are common between the servo writer and the data write 
elements allowing the elements to share a common gap line. For example, 
typical common wafer level simultaneous construction of data and servo 
write elements includes depositing on an appropriate ceramic substrate 
such as alumina titanium-carbide (Al.sub.2 O.sub.3 TiC) the first or 
bottom pole layer of high-moment, low coercivity magnetic material, such 
as permalloy, NiFe, or cobalt zirconium tantalum (CZT). An insulating, gap 
forming layer of alumina (Al.sub.2 O.sub.3) is then deposited. Using 
photolithography techniques, one or more layers of coils, displaced from 
where the front gap will be formed by lapping, are plated with the 
requisite insulation layers of baked photoresist. A top smoothing layer of 
baked photoresist above the coils is deposited and a layer of the same 
magnetic material used for the first magnetic layer is deposited thereon 
to form the top pole. A thick layer of alumina, sufficiently thick to 
allow lapping of the film side of the substrate to form a planar surface, 
is deposited and the film side of the wafer is lapped to achieve a planar 
surface. 
Likewise, the servo read elements can be embedded in the data read elements 
with the use of common thin film processing steps. The steps of the thin 
film process for forming both types of read elements are common between 
the servo read elements and the data read elements allowing for common 
formation and common gap lines for the servo read elements and data read 
elements as shown in FIG. 9. For example, typical common wafer level 
simultaneous construction of data or servo read elements includes 
depositing on an appropriate ceramic substrate, such as alumina 
titanium-carbide (Al.sub.2 O.sub.3 TiC), a first shield layer of high 
permeability, low coercivity magnetic material, such as permalloy, NiFe, 
or cobalt zirconium tantalum (CZT). An insulating, gap forming layer of 
alumina (Al.sub.2 O.sub.3) is then deposited. Using photolithography 
techniques, a patterned magnetoresistive read sensor sandwich consisting 
of very thin films of permalloy and magnetic and non-magnetic layers is 
deposited. A second alumina layer is then deposited and a layer of the 
same magnetic material used for the first magnetic layer is deposited 
thereon to form the top shield. Thereafter, a thick protective layer of 
alumina is deposited and lapped to a planar surface. 
Although increased servo track spacing reduces the ambiguity in 
identification of servo tracks and thus reduces the likelihood of 
misidentification due to a head slipping off track by one or more servo 
tracks, some ambiguity may still exist. Ambiguity of servo track 
identification can be eliminated by using identically written servo tracks 
but using different varied physical separations between the servo tracks 
to determine which servo track is being accessed. Such physical separation 
to unambiguously determine servo track identification is described below 
with reference to the alternate servo configurations shown in FIGS. 14-16. 
By providing variable spacing between pairs of servo tracks which can be 
written identically and simultaneously, each servo track can be uniquely 
identified utilizing contiguously configured servo read elements even 
though none of the servo tracks have distinguishing characteristics, i.e., 
such as, for example, varied frequency, density. 
Positive track identification with use of a single pass servo writer can be 
achieved by coding the layout of the servo tracks, i.e., to provide 
differentiated spacing between two or more servo track pairs or each servo 
track pair. One form of this is to increase the spacing one track pitch 
between each subsequent pair of servo tracks as described further below 
which can be written with a servo writer similar to that of FIG. 12 with 
spacing differentials between the teeth of the writer. 
A variable spaced servo track configuration using the differentiated 
spacing set forth above is shown in FIG. 14. The servo system 
configuration includes data bands 202 with a servo band 200 positioned at 
the center therebetween. The servo band 200 includes servo tracks 204 and 
multiple servo read elements 206. In accordance with the present 
invention, the center to center spacing between servo tracks of the 
adjacent servo track pair 210, 212 is about two data track pitches, and 
the center to center spacing between servo tracks of the servo track pair 
212, 214 is about three data track pitches. 
The guard bands 208 separate the coded servo tracks 204 from the data bands 
202 to allow the signal from the data band to be sufficiently reduced so 
as not to be interpreted as a servo signal accessible by the servo read 
elements. However, guard bands on the edges of the servo band 200 are 
typically not required if the servo tracks are written simultaneously and 
identically with the same monofrequency which is substantially different 
from the data frequencies. 
The servo track configuration as shown in FIG. 14 is shown in further 
detail in FIG. 15 minus the guard bands 208. Adjacent to the servo band 
200 and various positions of servo read elements 206, as shown in FIG. 14, 
is an algebraic code which illustrates the uniqueness of each position of 
the servo read elements 206 with respect to the differentially spaced 
servo tracks 204. As shown in FIG. 15, a monotonically increasing 
separation between servo tracks of pairs of adjacent servo tracks by an 
additional track from one servo track pair to a subsequent pair of servo 
tracks is shown. However, other codes may also be used. For example, the 
code could be a binary code of spacings of 1, 2, 4, 8 . . . between 
subsequent pairs of tracks or the pairs of adjacent servo tracks may be 
spaced at random. Further, multiples of the track pitch interval spacing 
may also be utilized. 
In operation, as illustrated in FIG. 15, servo read elements C and D are 
moved to a position whereat signals are received by servo read circuitry 
from servo read elements. The servo read circuitry may be similar to servo 
read circuitry 63, but any circuitry which can sense the position of 
adjacent servo read elements relative to the servo tracks may be utilized. 
The signals representative of each the multiple servo elements 206 may be 
multiplexed or cycled through to determine the adjacent servo read 
elements that are positioned adjacent a servo track. After adjacent servo 
read elements have locked on a particular servo track, such as elements C 
and D locking on the center of servo track 210, the outputs representative 
of each of the multiple servo read elements are cycled through to identify 
which servo track the elements C and D have locked on. For example, when 
the servo elements C and D have locked on servo track 210, the outputs of 
the multiple servo elements correspond to the code ABCD. The outputs are 
provided to a drive processing unit with which the head assembly 62 is 
utilized. In this manner, it is determined by the drive processing unit 
that the adjacent servo read elements C and D are locked onto servo track 
210. As similarly described previously with respect to the operation of 
the tapped servo read elements with reference to FIG. 8A, when elements C 
and D are positioned such that the signals therefrom are equal, the center 
of servo track 210 is detected and servo lock is achieved. Reading and 
writing functions may then be performed. 
As the servo read elements 206 are moved proximate the other servo tracks 
212 and 214, unique codes also identify which servo tracks the elements 
are locked onto. For example, in the last position shown, elements A and B 
are adjacent servo track 214 and the unique code ABCD are used to identify 
servo track 214. As such, in each position of the servo elements A, B, C, 
and D, a different code is available so as to unambiguously identify the 
servo track to which the pair of adjacent servo elements are locked. 
FIGS. 16 illustrates the progression for the next set of increased data 
tracks per servo band. For example, if a number of data tracks in a data 
band is 10, then the number of servo tracks 222 in servo band 220 is four 
with a center to center separation between the furthest apart servo bands 
being four data track pitches as shown in FIG. 16. As such, fourteen 
algebraic codes are available for illustrating the unique position of six 
servo read elements with respect to the servo tracks 222. 
In general, the number of servo read elements for use in the variably 
spaced servo track configurations is equal to at least K+1, wherein K is 
equal to the number of track pitches between the centers of the servo 
tracks for the pair of adjacent servo tracks which are farthest apart. For 
example, as shown in FIG. 15, the number of track pitches between the 
centers of the servo tracks 212 and 214 is three. Therefore, the number of 
servo read elements 206 required is at least four. Likewise, with the 
center to center spacing between the pair of servo tracks farthest apart 
being four track pitches, the minimum number of servo read elements is at 
least five. However, as shown in FIG. 16, in order to provide unique codes 
for each of the possible servo read element positions in the servo band to 
service individual data bands of 10 data tracks, at least 6 servo read 
elements are necessary. 
It should be readily apparent that the various elements as described with 
respect to the present invention may be utilized separately, together in a 
system, or with other servo configurations, and the present invention is 
limited only in accordance with the accompanying claims. For example, the 
differentially spaced servo track configurations as described with respect 
to FIGS. 14-16 may be utilized with servo read elements that are formed 
from a tapped single magnetoresistive element or may further include a 
servo read element configuration wherein such elements are not tapped, but 
rather separate heads are used. Further, for example, the servo writer 
which may be utilized to form a single pass to write the noncontiguous 
servo tracks at a mono-frequency as described herein need not be a part of 
the head assembly. Such servo tracks may be written in the factory as 
opposed to being written in situ. Likewise, the servo read circuitry, as 
previously described, may be utilized in conjunction with the variably 
spaced servo track configurations described with respect to FIGS. 14-16 
with modifications as would be known to one skilled in the art. 
Although the present invention has been described with reference to 
particular embodiments, one skilled in the art will recognize that changes 
and modifications may be made in form and detail therewith without 
departing from the scope of the invention as described in the accompanying 
claims.