Patent Publication Number: US-7903368-B2

Title: Tape cartridge having tape media with longitudinally shifted servo pattern for increased sampling rate

Description:
DOCUMENT INCORPORATED BY REFERENCE 
     Commonly assigned U.S. Pat. No. 5,689,384 is incorporated for its showing of a timing based servo system. 
     FIELD OF THE INVENTION 
     This invention relates to a tape cartridge having a servo pattern, and more particularly, to a magnetic tape of the tape cartridge having timing based servo band(s) extending in the longitudinal direction of the magnetic tape. 
     BACKGROUND OF THE INVENTION 
     Magnetic tape provides a means for physically storing data which may be archived or which may be stored in storage shelves of automated data storage libraries and accessed when required. The reading and/or writing of data in bands on magnetic recording tape requires precise positioning of a magnetic head. The magnetic head must be moved to, and maintained centered over, specific longitudinal data bands, as the magnetic tape is moved longitudinally past the magnetic head. The magnetic head is translated between bands in a lateral direction with respect to the longitudinal data bands. 
     A servo system is employed to move the magnetic head to and position the magnetic head in the center of the desired data band or bands, and to track follow the center of the desired data band or bands. The data bands are becoming increasingly smaller and closer together in order to increase the data band density and thereby increase data capacity of a given tape. Hence, it has become desirable to place the longitudinal defined servo bands at various locations across the full width of the tape, separated by groups of data bands. This allows the servo bands to be close to the data bands and limits offsets due to tape stretch, etc. This also allows a greater number of bands to be employed due to the greater precision of the relationship between the servo bands and the data bands. 
     SUMMARY OF THE INVENTION 
     A magnetic tape cartridge including magnetic tape with servo information is provided. The servo information comprises a plurality of parallel longitudinal servo bands that lie between a plurality of longitudinal data bands. The plurality of servo bands include odd servo bands and even servo bands, wherein each of the odd servo bands lie between each of the even servo bands. Each of the plurality servo bands include a plurality of frames, wherein each frame includes a plurality of bursts of transition stripes, and each burst having a first transition stripe. The first transition stripe of each burst of each the odd servo band is longitudinally shifted from the first transition stripe of each burst of each even servo band by a substantially equal distance, D, such that servo information of the odd servo bands is interleaved with the servo information from the even servo bands. 
     The frame includes a first burst of transition stripes in a first azimuthal orientation and a second burst of transition stripes in a second azimuthal orientation different than the first azimuthal orientation, followed by a third burst of transition stripes in the first azimuthal orientation and a fourth burst of transition stripes in the second azimuthal orientation and wherein a distance between the first transition stripe of the first burst and the first transition stripe of the third burst is a distance B. In one embodiment the second azimuthal orientation is opposite of the first azimuthal orientation. 
     In one embodiment the magnetic tape is configured for a tape drive having a plurality of servo read elements, the first transition stripe of each burst of each the odd servo band is longitudinally shifted from the first transition stripe of each burst of each the even servo band by a substantially equal distance, D, wherein 
               0.9   ⁢     B   X       ≤   D   ≤     1.1   ⁢     B   X             
and wherein X is a number servo read elements of the tape drive.
 
     Accordingly, in one embodiment the magnetic tape is configured for a tape drive having two servo read elements such that 0.45B≦D≦0.55. In another embodiment the magnetic tape is configured for a tape drive having three servo read elements such that 0.30B≦D≦0.37B. 
     In one embodiment the magnetic tape comprises five parallel longitudinal servo bands. Further the frame may further include a first burst of a group of five stripes in a first azimuthal orientation and a second burst of a group of five transitions in a second azimuthal orientation different than the first azimuthal orientation, followed by a third burst of a group of four transition stripes in the first azimuthal orientation and a fourth burst a group of four transition stripes in the second azimuthal orientation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic illustration of a magnetic tape having a timing based servo track, and of a magnetic head and servo system of a magnetic tape drive having multiple servo read elements; 
         FIG. 2  is a simplified diagrammatic illustration of a magnetic tape having a timing based servo track, and of a magnetic head and servo system of a magnetic tape drive having multiple servo read elements including indication of “A” and “B” signal intervals; 
         FIG. 3  an embodiment in accordance with the present disclosure of a diagrammatic illustration of a magnetic tape having a timing based servo track, and of a magnetic head and servo system of a magnetic tape drive having multiple servo read elements; 
         FIG. 4  is an embodiment in accordance with the present disclosure of a simplified diagrammatic illustration of a magnetic tape having a timing based servo track, and of a magnetic head and servo system of a magnetic tape drive having multiple servo read elements including indication of “A” and “B” signal intervals; 
         FIG. 5  is an illustration of a magnetic tape drive in accordance with the present disclosure; 
         FIG. 6  is a detailed illustration of a magnetic tape cartridge in accordance with the present disclosure; and 
         FIG. 7  is a detailed illustration of a servo head with three servo read amendments in accordance with another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following is intended to provide a detailed description of an example of the invention and should not be taken to be limiting of the invention itself. Rather, any number of variations may fall within the scope of the invention which is defined in the claims following the description. 
     Referring to  FIG. 1 , a timing based servo pattern is described on a magnetic tape, such as magnetic tape  20  wherein prerecorded magnetic parallel longitudinal servo bands  27  (e.g.  27   a ,  27   b ,  27   c ,  27   d , and  27   e ) lie between groups of longitudinal data tracks  29  (e.g.  29   a ,  29   b ,  29   c ,  29   d , and  29   e ). In addition, the magnetic tape  20  is provided with guard bands  48 ,  49  at the edges of the tape. The longitudinal direction is defined as the direction along the length of the magnetic tape  20 . The lateral direction is defined as the direction along the width of the magnetic tape  20  and is perpendicular to the longitudinal direction. The terms “band” and “track” are used interchangeably herein. Similarly, the terms “bands” and “tracks” are used interchangeably herein. 
     In the specific example of  FIG. 1 , five longitudinal timing based defined servo bands  27  are prerecorded on a magnetic tape  20  for track following at these positions. The pattern of magnetic transitions recorded in the defined servo bands is a repeated set of frames  38 , each of which are of different azimuthal orientations. For example, the pattern may comprise transitions slanted, or having an azimuthal orientation, in a first direction with respect to the longitudinal direction of the linear servo track, alternating with transitions having different slants, for example, in the opposite direction. The groups of transitions having the same azimuthal orientation and separated by gaps or spaces are referred to as “servo bursts” or simply as “bursts” (e.g. bursts  40 ,  41 ,  42 , and  43 ). Each servo burst contains a predetermined number of transition stripes per burst, which can be used in error detection and correction. 
     The head assembly  24  comprises a plurality of read and/or write elements  28  configured to read and/or write data on a magnetic tape with respect to sets of the longitudinal data tracks  29 . In the example of  FIG. 1 , a head assembly  24  comprises at least two narrow servo read elements  25 ,  26 , allowing two servo bands to be sensed simultaneously. The resulting outputs from both servo bands may be averaged or used redundantly to reduce error rates. When the servo read elements  25 ,  26  are properly positioned at the defined servo bands  27 , the read and write elements  28  are properly positioned to transfer data with respect to the data track location of the magnetic tape  20 . 
     Those skilled in the art will recognize that the dark slanted stripes represent magnetized areas of recorded magnetic flux that extend across the width of a servo track  27 , and that the edges of the stripes comprise flux transitions that are detected to generate a servo read element signal. The transitions have two magnetic polarities, on each edge of a stripe. When a servo read element crosses a transition of servo track  27 , e.g. along servo track centerline  50  of  FIG. 2 , it produces an analog signal pulse whose polarity is determined by the polarity of the transition. For example, the servo read element may produce positive pulses on the leading edge of each stripe (on encountering the transition of encountering the stripe), and negative pulses on the trailing edge (on encountering the transition on leaving the stripe). To reduce the chance for error, the servo system times only intervals between magnetic flux transitions having the same polarity. As one example, only transition pulses generated by the servo read element in moving across the leading edge of a stripe are used, and transition pulses generated by moving across the trailing edge of a stripe are ignored. Hence, herein, the term “transition” refers to edges of stripes, or equivalent, that result in the generation of signals having the same polarity. 
     The lateral positioning of the servo read element with respect to the timing based servo track is sensed based on a measure of time between two transitions having different slants, called the “A” distance, as compared to the time between two transitions having parallel slants, called the “B” distance. Referring to  FIG. 1  for example, the “A” distance may be measured based on the time between the first transition stripe of burst  40  and the first transition stripe of burst  41 . Further, in one example, the “B” distance is measured based on the time between the first transition stripe of burst  40  and the first transition stripe of burst  42 . One of ordinary skill in the art would understand that while in the above example the first transition stripe of each burst is used to determine the “A” and “B” distance, any transition stripe of the respective burst may be utilized. For example, the “A” and “B” distances may be determined based on the comparison of the second transition stripe of one burst against the second transition stripe of the other burst. The first transition stripe is defined herein as the first transition stripe the servo read element  25 ,  26  arrives at in the read direction. 
     More specifically, lateral position sensing within a defined servo band is achieved by deriving a ratio of these two servo pattern intervals. In particular, the lateral position may be the ratio of (1) the distance between transitions of bursts  40  and  41 , called the “A” distance, to (2) the distance between transitions of burst  40  and  42 , called the “B” distance. The distances are measured by the timing between the transitions at a constant velocity. Thus, as the tape head servo read elements  25 ,  26  move toward the lower edge of the tape  20 , the ratio of the time between the transitions of burst  40  and  41  to the time between the transitions of bursts  40  and  42  becomes greater, since the distance between the “A” transitions of the burst  40  and  41  is greater, while the distance between the “B” transitions of burst  40  and  42  remains unchanged. 
     It is important to note that the servo tracks  27  are typically generated by a servo writer having two spaced apart write elements of different slants, forming the “A” distance, which are pulsed simultaneously. Thus, the “A” geometric distance is determined photolithographically, and is therefore, independent of the timing or the velocity of the servo writer drive. 
     The tape is moved longitudinally across the head assembly  24  so that the servo tracks  27   a  and  27   b  are moved across the servo read elements  25  and  26 , respectively. When such movement occurs, the servo pattern of magnetic flux transitions is detected by the servo read elements  25  and  26  so that it generates two analog servo read element signals, one for each servo read element  25  and  26 . The analog servo read element signals for each servo read element  25  and  26  are provided via a servo signal lines  84  and  90  to signal decoders  86  and  92 , respectively. The respective signal decoders then process the servo read element signals and generate a position signal that is transmitted via position signal lines  88  and  94  to servo controller  80 . The servo controller  80  generates a servo control signal and provides it on control line(s)  82  to a servo positioning mechanism at head assembly  24 . The servo positioning mechanism responds to the control signal from the servo controller  80  by moving the assembly including servo read elements  25  and  26  laterally with respect to the servo track centerline  50  to reach the desired servo track or to maintain the servo read elements  25  and  26  center with respect to the servo track centerline  50 . 
     Servo detection logic of servo system  80  is configured to detect from the signals supplied on line(s)  82 , the relative timings of the laterally extending transitions, specifically including the transitions having different slants, sensed by the plurality of laterally spaced servo read elements  25  and  26  as the magnetic tape  20  is moved in the longitudinal direction. The servo detection logic is configured to determine from the relative timings of the sensed transitions the “A” distances and information regarding the relationship between the plurality of servo read elements  25  and  26  and the magnetic tape for at least one known set of laterally extending transitions having differing slants. 
       FIG. 2  shows simplified version of a timing based servo pattern on a magnetic tape, such as magnetic tape  20 . For purposes of simplifying the illustration each burst is shown in  FIG. 2  as a single line. In one embodiment the single line may represent the first transition stripe of each burst. 
     Similar to that described with respect to  FIG. 1 , the head assembly  24  comprises at least two narrow servo read elements  25 ,  26 , allowing two servo bands (e.g.  27   a  and  27   b ) to be sensed simultaneously. As mentioned above, when a servo read element (e.g. servo read element  25  and/or  26 ) crosses a transition of servo track  27 , e.g. along servo track centerline  50 , it produces an analog signal pulse whose polarity is determined by the polarity of the transition. 
     In the example illustrated in  FIG. 2 , transition stripe L 2 , having a first azimuthal orientation, is separated from transition stripe L 3 , having a second azimuthal orientation, by distance A. In one example, distance A may be 50 μm. Transition stripe L 1 , having a second azimuthal orientation, is separated from transition stripe L 3 , also having a second azimuthal orientation, by distance B. In one example, distance B may be 100 μm (“B” distance). 
     As illustrated in  FIG. 2 , in the prior art, each burst of transition stripes within one servo band (e.g.  27   a ) is longitudinally aligned with each burst of transition stripes of all servo bands (e.g.  27   b ,  27   c ,  27   d ,  27   e ). For example, the burst represented by transition stripe L 1  of servo band  27   a  aligns longitudinally with the burst represented by transition stripe M 1  of servo band  27   b  along x 1 . Similarly, the bursts represented by transition stripes L 2  and L 3  align longitudinally with the bursts represented by transition stripes M 2  and M 3 , respectively. 
     Servo read element  25  (as shown in  FIG. 1 ) measures the “A” distance along servo band  27   a  by detecting a signal as it crosses a transition stripe of a first azimuthal orientation of servo band  27   a  (e.g. transition stripe L 2 ) along servo track centerline  50  and then by detecting a signal as it crosses an adjacent transition stripe of a second azimuthal orientation of servo band  27   a  (e.g. transition stripe L 3 ). Similarly, servo read element  26  measures the “A” distance along servo band  27   b  by detecting a signal as it crosses a transition stripe of a first azimuthal orientation of servo band  27   b  (e.g. transition stripe M 2 ) along servo track centerline  50  and then by detecting a signal as it crosses an adjacent transition stripe of a second azimuthal orientation of servo band  27   b  (e.g. transition stripe M 3 ). Since the transition stripes L 3  and M 3  align longitudinally along the length of the magnetic tape  20  at x 2 , the servo read element  25  outputs servo information regarding distance “A” at the same time that servo read element  26  outputs information regarding distance “A”. Accordingly, servo information obtained from servo element  26  regarding an odd servo band is provided simultaneously with the servo information obtained from servo element  25  regarding an even servo band. 
     Furthermore, as illustrated in  FIG. 2 , servo read element  25  measures the “B” distance along servo band  27   a  by detecting a signal as it crosses a transition stripe of a second azimuthal orientation of servo band  27   a  (e.g. transition stripe L 1 ) along servo track centerline  50  and then by detecting a signal as it crosses an adjacent transition stripe of the second azimuthal orientation of servo band  27   a  (e.g. transition stripe L 3 ). Similarly, servo read element  26  measures the “B” distance along servo band  27   b  by detecting a signal as it crosses a transition stripe of a second azimuthal orientation of servo band  27   b  (e.g. transition stripe M 1 ) along servo track centerline  50  and then by detecting a signal as it crosses an adjacent transition stripe of the first azimuthal orientation of servo band  27   b  (e.g. transition stripe M 3 ). Again, since the transition stripes L 3  and M 3  align longitudinally along the length of the magnetic tape  20  at x 2 , the servo read element  25  outputs servo information regarding distance “B” at the same time that servo read element  26  outputs information regarding distance “B”. Accordingly, servo information obtained from servo element  26  regarding an odd servo band is provided simultaneously with the servo information obtained from servo element  25  regarding an even servo band. 
     The sample rate, Fs, of the servo read element signal is determined by the length of the servo pattern and the tape velocity. The sampling rate, Fs may be expressed as: 
             Fs   =     velocity   distance           
wherein the velocity is the velocity of the magnetic tape and the distance is the distance between two transition lines of the servo pattern.
 
     For example, assuming a tape velocity of 2 m/sec, a distance “A” of 50 μm, and a distance “B” of 100 μm, the servo read elements  25  and  26  would output servo information at a rate of 20,000 samples every second. 
     The sample rate required for proper serving is determined by the rest of the components of the track-following servo loop. In order to support a high bandwidth track following the servo control system requires a high sampling rate servo feedback signal. The high sampling rate provides up-to-date, accurate information of the servo read element position, and therefore, supports a higher servo bandwidth and thus a much better controlled servo system. As the magnetic tape  20  velocity slows to match with the slower data transfer host system (referred to as speed matching) the sampling rate becomes slower and results in too slow of a sampling rate to maintain high bandwidth track following system. 
     Thus, what is presented is tape cartridge having a servo pattern with a higher longitudinal density of servo information such that a higher servo sampling rate is realized. The higher sampling rate provides up-to-date accurate information of servo read element position and, therefore, ensures a higher servo bandwidth system with increased control. 
     In accordance with the present disclosure  FIG. 3  describes a timing based servo pattern on a magnetic tape, such as magnetic tape  320  wherein prerecorded magnetic parallel longitudinal servo tracks  327   a ,  327   b ,  327   c ,  327   d , and  327   e  (also referred to herein as  327 ) lie between groups of longitudinal data tracks  329   a ,  329   b ,  329   c ,  329   d , and  329   e  (herein after referred to as  329 ). In addition, the prerecorded magnetic parallel servo tracks or bands comprise odd servo bands and even servo bands. The odd servo bands lie between each of the even servo bands. For example, servo bands  327   a ,  327   c  and  327   e  may be defined as even servo bands and servo bands  327   b , and  327   d  may be defined as odd servo bands. 
     The magnetic tape  320  is also provided with guard bands  348 ,  349  at the edges of the tape. The longitudinal direction is defined as the direction along the length of the magnetic tape  320 . The lateral direction is defined as the direction along the width of the magnetic tape  320  and is perpendicular to the longitudinal direction. 
     In the example of  FIG. 3 , five longitudinal timing based defined servo bands  327  are prerecorded on a magnetic tape  320  for track following at these positions. The pattern of magnetic transitions recorded in the defined servo bands is a repeated set of frames  338 , each of which are of different azimuthal orientations. For example, the pattern may comprise transitions slanted, or having an azimuthal orientation, in a first direction with respect to the longitudinal direction of the linear servo track, alternating with transitions having different slants, for example, in the opposite direction. The groups of transitions having the same azimuthal orientation and separated by gaps or spaced are referred to as “servo bursts” or simply as “bursts” (e.g. bursts  340 ,  341 ,  342 , and  343 ). Each servo burst contains a predetermined number of transition stripes per burst, which can be used in error detection and correction. As shown in  FIG. 3 , the present embodiment comprises a first burst of a group of five stripes in a first azimuthal orientation and a second burst of a group of five transitions in a second azimuthal orientation different than the first azimuthal orientation, followed by a third burst of a group of four transition stripes in the first azimuthal orientation and a fourth burst a group of four transition stripes in the second azimuthal orientation. 
     The head assembly  324  comprises a plurality of read and/or write elements  328  configured to read and/or write data on a magnetic tape with respect to sets of the longitudinal data tracks  329 . When the servo read elements  325 ,  326  are properly positioned at the defined servo bands  327 , the read and write elements  328  are properly positioned to transfer data with respect to the data track location of the magnetic tape  320 . 
     The lateral positioning of the servo read element with respect to the timing based servo track is sensed based on a measure of time between two transitions having different slants, called the “A” distance, as compared to the time between two transitions having parallel slants, called the “B” distance. Referring to  FIG. 3  for example, the “A” distance may be measured based on the time between the first transition stripe of burst  340  and the first transition stripe of burst  341 . Further, in one example, the “B” distance is measured based on the time between the first transition stripe of burst  340  and the first transition stripe of burst  342 . One of ordinary skill in the art would understand that while in the above example the first transition stripe of each burst is used to determine the “A” and “B” distance, any transition stripe of the respective burst may be utilized. For example, the “A” and “B” distances may be determined based on the comparison of the second transition stripe of one burst against the second transition stripe of the other burst. 
     More generally, lateral position sensing within a defined servo band is achieved by deriving a ratio of these two servo pattern intervals. Specifically, the lateral position may be the ratio of (1) the distance between transitions of bursts  340  and  341 , called the “A” distance, to (2) the distance between transitions of burst  340  and  342 , called the “B” distance. The distances are measured by the timing between the transitions at a constant velocity. Thus, as the tape head servo read elements  325 ,  326  move toward the lower edge of the magnetic tape  320 , the ratio of the time between the transitions of burst  340  and  341  to the time between the transitions of bursts  340  and  342  becomes greater, since the distance between the “A” transitions of the burst  340  and  341  is greater, while the distance between the “B” transitions of burst  340  and  342  remains unchanged. 
     As illustrated in  FIG. 3 , each burst of transition stripes within the odd servo bands (e.g.  327   b  and  327   d ) is longitudinally shifted or is offset from each burst of transition stripes of the even servo bands (e.g.  327   a ,  327   c , and  327   e ) such that the servo information of said odd servo bands is interleaved with the servo information from the even servo bands. 
       FIG. 4  shows simplified version of a timing based servo pattern on a magnetic tape, such as magnetic tape  320 . For purposes of simplifying the illustration each burst is shown in  FIG. 4  as a single line. In one embodiment the single line may represent the first transition stripe of each burst. 
     Similar to that described with respect to  FIG. 3 , the head assembly  324  comprises at least two narrow servo read elements  325 ,  326 , allowing two servo bands (e.g.  327   a  and  327   b ) to be sensed simultaneously. As mentioned above, when a servo read element (e.g. servo read element  325  and/or  326 ) crosses a transition of servo track  327 , e.g. along servo track centerline  350 , it produces an analog signal pulse whose polarity is determined by the polarity of the transition. 
     In the example illustrated in  FIG. 4  transition stripe L 2 , having a first azimuthal orientation, is separated from transition stripe L 3 , having a second azimuthal orientation, by distance “A”. In one example, distance “A” may be 50 μm. Transition stripe L 1 , having a second azimuthal orientation, is separated from transition stripe L 3 , also having a second azimuthal orientation, by distance “B”. In one example, distance “B” may be 100 μm. 
     As illustrated in  FIG. 4 , each burst of transition stripes within the odd servo bands (e.g.  327   b  and  327   d ) is longitudinally shifted or is offset from each burst of transition stripes of the even servo bands (e.g.  327   a ,  327   c , and  327   e ). For example, the burst represented by transition stripe M 1  of servo band  327   b  is longitudinally shifted from the burst represented by transition stripe L 1  of servo band  327   a  by a distance “D”. Similarly, the bursts represented by transition stripe L 2  and L 3  are longitudinally shifted from the bursts represented by transition stripe M 2  and M 3  by a distance “D”, respectively. It should be understood by one of ordinary skill in the art, that while not labeled,  327   c  and  327   e  contain L 1 , L 2 , and L 3 . As shown in  FIG. 4  transitions L 1 , L 2 , and L 3  of  327   c  and  327   e  align with L 1 , L 2 , and L 3  of  327   a , respectively. Similarly,  327   d  contains M 1 , M 2 , and M 3 . As shown in  FIG. 4  transitions M 1 , M 2 , and M 3  of  327   d  align with M 1 , M 2  and M 3  of  327   b , respectively. 
     Servo read element  325  measures the “A” distance along servo band  327   a  by detecting a signal as it crosses a transition stripe of a first azimuthal orientation of servo band  327   a  (e.g. transition stripe L 2 ) along servo track centerline  350  and then by detecting a signal as it crosses an adjacent transition stripe of a second azimuthal orientation of servo band  327   a  (e.g. transition stripe L 3 ). Similarly, servo read element  326  measures the “A” distance along servo band  327   b  by detecting a signal as it crosses a transition stripe of a first azimuthal orientation of servo band  327   b  (e.g. transition stripe M 2 ) along servo track centerline  350  and then by detecting a signal as it crosses an adjacent transition stripe of a second azimuthal orientation of servo band  327   b  (e.g. transition stripe M 3 ). Since the transition stripes L 3  and M 3  are longitudinally shifted from each other by a distance “D”, the servo read element  325  outputs servo information regarding distance “A” at a different time than when servo read element  326  outputs information regarding distance “A” such that the servo information of the odd servo bands is interleaved with the servo information from the even servo bands. Accordingly, servo information obtained from servo element  326  regarding an odd servo band is not provided simultaneously with the servo information obtained from servo element  325  regarding an even servo band. 
     Furthermore, as illustrated in  FIG. 4 , servo read element  325  measures the “B” distance along servo band  327   a  by detecting a signal as it crosses a transition stripe of a second azimuthal orientation of servo band  327   a  (e.g. transition stripe L 1 ) along servo track centerline  350  and then by detecting a signal as it crosses an adjacent transition stripe of the second azimuthal orientation of servo band  327   a  (e.g. transition stripe L 3 ). Similarly, servo read element  326  measures the “B” distance along servo band  327   b  by detecting a signal as it crosses a transition stripe of a second azimuthal orientation of servo band  327   b  (e.g. transition stripe M 1 ) along servo track centerline  350  and then by detecting a signal as it crosses an adjacent transition stripe of the second azimuthal orientation of servo band  327   b  (e.g. transition stripe M 3 ). Again, since the transition stripes L 3  and M 3  are longitudinally shifted by a distance “D” the servo read element  325  outputs servo information regarding distance “B” at a time different than when the servo read element  326  outputs information regarding distance “B”. Accordingly, servo information obtained from servo element  326  regarding an odd servo band is not provided simultaneously with the servo information obtained from servo element  325  regarding an even servo band. 
     Distance “D” may be expressed by the following equation, wherein X is the number of laterally spaced servo read elements of magnetic tape drive: 
                       [       1   X     -     .1   ⁢     (     1   X     )         ]     ⁢   B     ≤   D   ≤       [       1   X     +     .1   ⁢     (     1   X     )         ]     ⁢   B             (     Equation   ⁢           ⁢   1     )               
wherein X is the number of laterally spaced servo read elements of a magnetic tape drive configured to read and/or write to magnetic tape  320 . Equation 1 may be simplified as follows:
 
     
       
         
           
             
               
                 
                   
                     0.9 
                     ⁢ 
                     
                       B 
                       X 
                     
                   
                   ≤ 
                   D 
                   ≤ 
                   
                     1.1 
                     ⁢ 
                     
                       
                         B 
                         X 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
     In one embodiment, tape  320  is to be utilized in a magnetic tape drive having two laterally spaced apart servo read elements  325 ,  326 . In this embodiment the first transition stripe of each burst of each odd servo band is longitudinally shifted from the first transition stripe of each burst of each even servo band by a substantially equal distance “D”, wherein D is between 0.45B and 0.55B. In a further embodiment the distance “D” is approximately 0.50B. Therefore, in the embodiment in which two servo read elements read two different servo bands (e.g.  327   a  and  327   b ) the head assembly  324  will output servo information for the even servo band  327   a  at a different time than that of any adjacent servo band (e.g. odd servo band  327   b ). Similarly, servo read element  325  will output servo information for the odd servo band  327   b  at a different time than that of any adjacent servo bands (e.g.  327   a  and  327   c ). Therefore, each burst of transition stripes within the odd servo bands (e.g.  327   b  and  327   d ) is longitudinally shifted or is offset from each burst of transition stripes of the even servo bands (e.g.  327   a ,  327   c , and  327   e ) such that the servo information of said odd servo bands is interleaved with the servo information from the even servo bands. The above described pattern provides a sampling rate that is doubled over the prior art pattern. 
     For example in the present embodiment, assuming a tape velocity of 2 m/sec and wherein distance “A” is 50 μm, and distance “B” is 100 μm, the servo read elements  325  and  326 , would output servo information at a rate of 40,000 samples every second because the odd servo band pattern is shifted longitudinally shifted from the even servo pattern by a distance of “D”, wherein 0.45B≦D≦0.55B. 
     Returning to  FIG. 3 , the tape is moved longitudinally across the head assembly  324  so that the servo tracks  327   a  and  327   b  are moved across the servo read elements  325  and  326 , respectively. When such movement occurs, the servo pattern of magnetic flux transitions is detected by the servo read elements  325  and  326  so that it generates two analog servo read element signals, one for each servo read elements  325  and  326 . As described above, in the present embodiment the first transition stripe of each burst of each odd servo band (e.g.  327   b ) is longitudinally shifted from the first transition stripe of each burst of said even servo band ( 327   a ) by a substantially equal distance, “D”, such that servo information of the odd servo band ( 327   b ) is interleaved with said servo information from the even servo band ( 327   a ). The analog servo read element signals for each servo read elements  325  and  326  are provided via a servo signal lines  384  and  390  to signal decoders  386  and  392 , respectively. Because of the longitudinal shift the servo signals for the even servo band ( 327   a ) and odd servo band ( 327   b ) are generated at different times and the respective signal decoders process the servo read element signals separately and generate a position signal that is transmitted via position signal lines  388  and  394  to servo controller  380 . The servo controller  380  generates a servo control signal for each servo band (e.g.  327   a  and  327   b ) and provides it on control line(s)  382  to a servo positioning mechanism at head assembly  324 . The servo positioning mechanism responds to the control signal from the servo controller  380  by moving the assembly including servo read elements  325  and  326  laterally with respect to the servo track centerline  350  for each servo band respectively (e.g.  327   a  and  327   b ) to reach the desired servo track or to maintain the servo read elements  325  and  326  center with respect to the servo track centerline  350 . 
     Servo detection logic of servo controller  380  is configured to detect from the signals supplied on line(s)  382 , the relative timings of the laterally extending transitions, specifically including the transitions having different slants, sensed by the plurality of laterally spaced servo read elements  325  and  326  as the magnetic tape  320  is moved in the longitudinal direction. The servo detection logic is configured to determine from the relative timings of the sensed transitions the “A” distances and information regarding the relationship between the plurality of servo read elements  325  and  326  and the magnetic tape for at least one known set of laterally extending transitions having differing slants. 
     A magnetic tape drive  100  is illustrated in  FIG. 5  configured to read and/or write data to a magnetic tape  320 , for example, from a magnetic tape cartridge  103 . The magnetic tape drive  100  is configured to receive the magnetic tape cartridge  103 , and the magnetic tape  320  is guided along a tape path from the magnetic tape cartridge, past a head assembly  324 , to a take up reel  105 . The magnetic tape  320  may be guided by tape guide rollers  110  along the tape path and constrained laterally by the tape guide rollers as the magnetic tape is moved longitudinally between the magnetic tape cartridge  103  and the take up reel  105 , for example, by a drive system comprising drive motors and a servo drive control (not shown). 
     Although the magnetic tape  320  is constrained laterally by the tape guide rollers  110 , some minor lateral movement may still occur at the head assembly  324 . Further, the magnetic tracks may have some minor lateral movement on the magnetic tape. A servo system  380  is configured to move the head assembly  324 , comprising the servo read elements  325  and  326  and read and/or write heads  328  of  FIGS. 3 and 4 , laterally with respect to the magnetic tape  320  in accordance with the information relating to the lateral position, discussed above, for example, to track follow the servo tracks of the magnetic tape  320 . 
     Magnetic tape cartridge  103  is illustrated in further detail in  FIG. 6 . The magnetic tape cartridge  103  may include a cartridge memory (CM)  614  (shown in cutaway) and magnetic tape  320  (shown in phantom) wound on a hub  612  of a reel  613 . If present, the cartridge memory  614  may comprise electrical contacts to allow a library (not shown) and/or magnetic tape drive  100  (as seen in  FIG. 5 ) to access the contents of the cartridge memory  614 . Alternatively, the cartridge memory  614  may comprise a contactless interface such as induction, radio frequency, or optical. In one embodiment, the cartridge memory  614  comprises an RFID tag. The cartridge memory  614  may be used to hold information about the tape cartridge  103 , the magnetic tape  320  in the tape cartridge  103 , and/or data on the magnetic tape  320 . Examples of tape cartridges are a cartridge based on LTO (Linear Tape Open) technology, such as the IBM TotalStorage LTO Ultrium Data Cartridge, and a cartridge based on IBM&#39;s 3592 technology, such as the IBM 3592 Enterprise Tape Cartridge. As will be appreciated, the tape cartridge  103  may be a magnetic tape cartridge having a dual reel implementation (in which the tape is fed between reels within the cartridge) or single reel implementation, such as illustrated in  FIG. 6 , in which the magnetic tape  320  is wound on a reel  613  within the magnetic tape cartridge  103 . For example, when the magnetic tape cartridge  103  is loaded into a magnetic tape drive (e.g. magnetic tape drive  100 ), the tape is fed between the cartridge reel  613  and a take up reel  105  located in the magnetic tape drive  100 . While exemplary tape cartridges based on the LTO and 3592 formats have been provided, it will be appreciated that the description is not limited by tape format. Examples of other tape formats include DLT, SDLT, 9840, 9940, T10000, AIT, and the like. 
     As discuss above, the magnetic tape  320  of tape cartridge  103 , has servo information in prerecorded magnetic longitudinal servo tracks for track following at these positions. Each burst of transition stripes within the odd servo bands (e.g.  327   b  and  327   d ) is longitudinally shifted or is offset from each burst of transition stripes of the even servo bands (e.g.  327   a ,  327   c , and  327   e ) by a substantially equal distance “D” as defined by Equation 2 above. 
     Since the transition stripes are longitudinally shifted from each other by a distance “D”, the servo read element  325  outputs servo information regarding distance “A” at a different time than when servo read element  326  outputs information regarding distance “A”. Similarly, the servo read element  325  outputs servo information regarding distance “B” at a different time than when servo read element  326  outputs information regarding distance “B”. Accordingly, servo information obtained from servo element  326  regarding an odd servo band is not provided simultaneously with the servo information obtained from servo element  325  regarding an even servo band. Therefore, the servo information of the odd servo bands is interleaved with the servo information from the even servo bands. 
     In one embodiment the distance “D” is between 0.45B and 0.55B. In a further embodiment the distance “D” is 0.50B. The above described pattern on a magnetic tape  320  of tape cartridge  103  provides a sampling rate that is doubled over the prior art patterns. 
     For example, in the present embodiment, assuming a tape velocity of 2 m/sec, a distance “A” of 50 μm, and a distance “B” of 100 μm, the servo read elements  325  and  326 , would output servo information at a rate of 40,000 samples every second since the odd servo band pattern is shifted longitudinally shifted from the even servo pattern by a distance of “D”, wherein 0.45B≦D≦0.6B. 
     While the above described embodiment discusses a head assembly comprising two servo read elements, a head assembly may comprise any number of servo elements. For example, in another embodiment, the head assembly  324  comprises three servo read elements, ( 325 ,  326 , and  330 ) as shown in  FIG. 7 . Accordingly, each burst of transition stripes within one servo band is shifted or is offset a substantially equal distance “D” from the burst of transition stripes of the previous servo band. In one embodiment, in which three servo read elements are utilized the distance “D” is between 0.30B and 0.37B as described by Equation 2. In a further embodiment, the distance “D” is approximately 0.33B. 
     For example, each burst of transition stripes of servo band  327   b  will be shifted longitudinally a distance “D” of approximately 0.33B from each burst of transition stripes of servo band  327   a . Similarly, each burst of transition stripes of servo band  327   c  will be shifted longitudinally a distance “D” of approximately 0.33B from each burst of transition stripes of servo band  327   b . Further, each burst of transition stripes of servo band  327   d  will be shifted longitudinally a distance “D” of approximately 0.33B from each burst of transition stripes of servo band  327   c  such that the transition stripes of servo band  327   d  is aligned with the transition stripes of servo band  327   a . Finally, each burst of transition stripes of servo band  327   e  will be shifted longitudinally a distance “D” approximately 0.33B from each burst of transition stripes of servo band  327   d  such that the transition stripes of servo band  327   e  is aligned with the transition stripes of servo band  327   b.    
     Similar to that discussed above with respect to  FIGS. 3 and 4 , since the transition stripes are longitudinally shifted from each other by a distance “D”, each of the servo read elements,  325 ,  326 , and  330 , output servo information regarding distances “A” and “B” at a different time than any adjacent servo band. For example, in the embodiment in which three servo read elements read three different servo bands (e.g.  327   a ,  327   b , and  327   c ) the head assembly  324  of  FIG. 7  will output servo information for servo band  327   b  at a different time than that any adjacent servo band (e.g.  327   a  and  327   c ) such that the servo information of said odd servo bands is interleaved with the servo information from the even servo bands, and specifically, that the servo information of a servo band is interleaved with the servo information from any adjacent servo band. The above described pattern provides a sampling rate that is tripled over the prior art pattern. 
     For example, in the present embodiment, assuming a tape velocity of 2 msec, a distance “A” of 50 μm, and a distance “B” of 100 μm, the servo read elements,  325 ,  326 , and  330 , would output servo information at a rate of 60,000 samples every second since each burst of transition stripes within one servo band is shifted or is offset a substantially equal distance “D” from the burst of transition stripes of the previous servo band, wherein 0.30 B≦D≦0.37B. 
     It should be understood by one of ordinary skill in the art that while the above description describes magnetic transition stripes recorded on magnetic tape, it should be understood that the servo bands  327  may comprise any of several types of longitudinal servo patterns as is known to those of skill in the art. 
     While the present embodiment describes servo bands  327   a ,  327   c , and  327   e  as even servo bands and  327   b , and  327   d  as odd servo bands, it should be understood by one of ordinary skill in the art that  327   a ,  327   c , and  327   e  may be defined as odd servo bands and  327   b , and  327   d  may be defined as even servo bands. Rather, it is only important that each burst of transition stripes within one servo band (is longitudinally shifted or is offset from each burst of transition stripes of any adjacent servo band by a substantially equal distance, “D”. 
     Further, while the present disclosure describes a magnetic tape  320  having five servo bands and four data bands, the present disclosure may be practiced on any magnetic tape having a plurality of servo bands. 
     The logic discussed above may comprise any suitable logic arrangement known to those of skill in the art. Further, those of skill in the art will understand that differing specific component arrangements may be employed than those illustrated herein. 
     While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein changes and modifications may be made without departing from this invention and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this invention. Furthermore, it is to be understood that the invention is solely defined by the appended claims.