Patent Publication Number: US-7724465-B2

Title: Tape heads for use with multiple tape formats

Description:
RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 11/855,899, filed Sep. 14, 2007 now U.S. Pat. No. 7,570,450, which is herein incorporated by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to magnetic head structures, and more particularly, this invention relates to a magnetic head structure capable of reading and/or writing in multiple formats. 
   BACKGROUND OF THE INVENTION 
   Business, science and entertainment applications depend upon computing systems to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical and convenient means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in hundreds of gigabytes on 896 or more data tracks. 
     FIG. 1  illustrates a traditional flat-lapped bi-directional, two-module magnetic tape head  100 , in accordance with the prior art. As shown, the head includes a pair of bases  102 , each equipped with a module  104 . The bases are typically “U-beams” that are adhesively coupled together. Each module  104  includes a substrate  104 A and a closure  104 B with readers and writers  106  situated therebetween. In use, a tape  108  is moved over the modules  104  along a tape bearing surface  109  in the manner shown for reading and writing data on the tape  108  using the readers and writers  106 . Conventionally, a partial vacuum is formed between the tape  108  and the tape bearing surface  109  for maintaining the tape  108  in close proximity with the readers and writers  106 . 
     FIG. 2A  illustrates the tape bearing surface  109  of one of the modules  104 . The tape  108  is shown in dashed lines. The module is long enough to be able to support the tape as the head steps between data tracks. 
   As shown, the tape  108  includes four data bands (Band  0 - 3 ) that are defined between servo tracks  202 . Each data band may include a number of data tracks, for example 224 data tracks (not shown). During read/write operations, the elements  106  are positioned within one of the data bands. Outer readers, sometimes called servo readers, read the servo tracks  202 . The servo signals are in turn used to keep the elements  106  aligned with a particular track during the read/write operations. Typically, a coarse positioner (worm gear, etc.) places the head generally adjacent a given data track, then a fine positioner (voice coil, etc.) keeps the heads aligned using the servo tracks. 
     FIG. 2B  depicts a plurality of read/write elements  106  formed in a gap  208  on the module  104  of  FIG. 2A . As shown, the array of elements  106  includes, for example, sixteen writers  209 , sixteen readers  210  and two servo readers  212 . As noted by considering FIGS.  1  and  2 A-B together, each module  104  will include a complementary set of elements  106 . 
   One designing magnetic storage systems, such as tape storage systems, strives to increase the data density of the medium. As a means for adding more data to a given area of a magnetic medium, succeeding generations of tape formats are born. Typically, newer formats may include more data bands as well as more data tracks per data band and/or width of the tape, and also improvements in data linear density. 
   On any head, both the spacing between the elements and the element dimensions conform to a particular tape format. Usually, a head designed for one format will not work with a tape written in another format, as the servo readers usually will not align with the servo tracks. In addition the data elements may not align with the written tracks. Accordingly, one wishing to keep data stored on a magnetic medium in one format but wishing to move to equipment in a new format must either keep an operational drive designed for the earlier format, or transfer the data to a medium in the new format. 
   One known attempt to provide a multi-format head  300  is shown in  FIG. 3 . As shown, the head  300  includes four modules  302 A,  302 B,  303 A,  303 B aligned parallel to the direction of tape travel. The outer pair of modules  302 A,  302 B each have an array of elements  304 A,  304 B arranged according to a first tape format, while the inner pair of modules  303 A,  303 B each have an array of elements  306 A,  306 B for a second tape format, the second tape format different than the first tape format. In both pairs, the complementary elements ( 304 A with  304 B,  306 A with  306 B) are displaced from each other in the direction of tape travel. However, these types of heads are very expensive to manufacture, as several independent modules  302 A,  302 B,  303 A,  303 B must first be fabricated. Also, once manufactured, the modules  302 A,  302 B,  303 A,  303 B must be precisely aligned, considering the critical wrap angles between the modules as well as the outer wrap angles. In addition, because of the larger spacing between the outer modules  302 A,  302 B, the head will be more susceptible to errors due to tape wobble. For example, in read-while-write operation, the readers on the trailing module  302 B read the data that was just written by the leading module  302 A so that the system can verify that the data was written correctly. If the data is not written correctly, the system recognizes the error and rewrites the data. However, the tape does not move across the head perfectly linearly. Rather, the tape may shift back and forth, or “wobble,” as it crosses the tape bearing surfaces, resulting in dynamic skew, or misalignment of the trailing readers with the leading writers. The farther the readers are behind the writers, the more chance that track misregistration will occur. If it does occur, the system may incorrectly believe that a write error has occurred. 
   Another known attempt to provide a multi-format head  400  is shown in  FIG. 4 . This tape head  400  is configured as a Read-Read-Write (R-R-W) head. Tape head  400  includes merged primary tape format read/write elements  404 A,  404 B and secondary tape format read elements  406 A,  406 B on each module  402 A,  402 B. In this instance, head  400  is capable of reading a secondary format corresponding to secondary format read elements  406 A,  406 B. Head  400  is further capable of both reading and writing with the primary format corresponding to primary read/write elements  404 A,  404 B. 
   With continued reference to  FIG. 4 , the primary and secondary elements  404 A,  404 B,  406 A,  406 B are aligned parallel to the direction of tape travel. Typically, each row of elements is fabricated in sequential fabrication sequences. For example, elements  404 A,  404 B may be formed first. Then the secondary elements  406 A,  406 B are fabricated above the primary elements  404 A,  404 B. However, this type of “stacked” head is complex and expensive to fabricate, as each row of elements  404 A,  404 B,  406 A,  406 B must be fabricated independently. Further, an error in processing late in the fabrication process can result in an expensive loss. Additionally, the electrical connections that would be necessary to traverse the multiple layers for so many devices would be very complex. 
   In addition to fabrication issues, modules implementing stacked rows of element also suffer from reliability issues. For instance, the head will run hotter, as the heat sinking effect of the substrate will be reduced. Particularly, if the upper array is being used, heat will have to travel through several layers of devices do reach the substrate. A further issue is the thick gap that would be required in order to accommodate stacked arrays. Tape irregularities tend to droop slightly into this gap and erode the elements. This produces head-tape spacing problems, such as declining signal resolution. Gap wear can also lead to debris deposition issues such as shorting. 
   There is accordingly a clearly-felt need in the art for a magnetic head assembly capable of reading and/or writing in multiple formats, yet that is simple and less expensive to manufacture. It would be desirable to be able to read and write multiple formats for such things as backward compatibility, as well as compatibility across competing formats. 
   SUMMARY OF THE INVENTION 
   A magnetic head according to one embodiment includes an array of elements, the elements being selected from a group consisting of data readers, data writers, and combinations thereof, wherein a first subset of the elements is operable for reading or writing data in a first tape format, wherein a second subset of the elements is operable for reading or writing data in a second tape format, at least some of the elements being present in both subsets, wherein a number of servo bands supported in each of the formats is one more than a number of data bands on a medium written in the particular format. 
   A magnetic head according to another embodiment includes a first array of elements associated with a first tape format, the elements of the first array being selected from a group consisting of data readers, data writers, and combinations thereof, a second array of elements interspersed with the first array of elements, the elements of the second array being selected from a group consisting of data readers, data writers, and combinations thereof, the second array of elements and a subset of the first array of elements being associated with a second tape format; and servo readers for reading servo bands on a tape, wherein a spacing of the servo bands on a tape written in the first format is different than a spacing of servo bands on a tape written in the second format. 
   A magnetic head according to yet another embodiment includes an array of elements, the elements being selected from a group consisting of data readers, data writers, and combinations thereof, wherein a first subset of the elements is operable for reading or writing data in a first tape format, wherein a second subset of the elements is operable for reading or writing data in a second tape format, at least some of the elements being present in both subsets, wherein the elements are aligned laterally along a line transverse to the direction of travel of the magnetic medium over the head, wherein a center-to-center spacing of the elements in the first subset of elements is at least one of an integer multiple and an integer ratio of a center-to-center spacing of the elements in the second subset of elements. 
   Any of the various embodiments may be implemented in a tape drive system, which may generally include a magnetic head; a drive mechanism for passing a magnetic recording tape over the head; and a controller in communication with the head. 
   Other aspects and advantages of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and advantages of the present invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings. 
     Prior Art  FIG. 1  is a side view of a traditional flat-lapped magnetic tape head, in accordance with the prior art. 
     Prior Art  FIG. 2A  is a tape bearing surface view taken from Line  2 A of  FIG. 1 . 
     Prior Art  FIG. 2B  is a detailed view taken from Circle  2 B of  FIG. 2A . 
     Prior Art  FIG. 3  is a tape bearing surface view of a head including multiple format read/write elements on different modules. 
     Prior Art  FIG. 4  is a tape bearing surface view of a head including multiple format read/write element arrays on the same module. 
       FIG. 5  is a tape bearing surface view of a tape head including two subsets of elements on the same module, each subset being adapted for a different format. 
       FIG. 6  is a detailed view taken from Circle  6  of  FIG. 5  according to one embodiment. 
       FIG. 7  is a detailed view of a tape bearing surface of a tape head according to another embodiment. 
       FIG. 8  is a side view of a tape head having two modules according to one embodiment. 
       FIG. 9  is a side view of a tape head having three modules according to one embodiment. 
       FIG. 10  is a schematic diagram of a tape drive system according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The following description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations. 
   Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc. 
   The following description discloses several preferred embodiments of tape-based storage systems, as well as operation and/or component parts thereof. 
   While the following description will be described in terms of a tape storage system for clarity and to place the invention in context, it should be kept in mind that the teachings herein may have broad application to all types of magnetic recording. 
   The embodiments described below disclose a new head design that is capable of reading and/or writing to magnetic media such as magnetic tape in multiple formats. For example, the head can write and/or read data in both legacy and advanced formats, and in doing so can enable full backward compatibility with legacy media types. This is an important criterion for customers wishing to move to a new format yet having data stored on media in an older format. 
   A magnetic head according in one general approach includes an array of elements, the elements being selected from a group consisting of data readers, data writers, and combinations thereof. A first subset of the elements is operable for reading and/or writing data in a first tape format, while a second subset of the elements is operable for reading and/or writing data in a second tape format, at least some of the elements being present in both subsets. A spacing of servo bands on a tape written in the first format is different than a spacing of servo bands on a tape written in the second format. 
   A magnetic head according to another general approach includes a first array of elements associated with a first tape format, the elements of the first array being selected from a group consisting of data readers, data writers, and combinations thereof, and a second array of elements interspersed with the first array of elements, the elements of the second array being selected from a group consisting of data readers, data writers, and combinations thereof, the second array of elements and a subset of the first array of elements being associated with a second tape format. Also present are servo readers for reading servo bands on a tape, where a number of servo bands supported in each of the formats is one more than a number of data bands in the particular format. 
   A magnetic head according to yet another general embodiment includes an array of elements, the elements being selected from a group consisting of data readers, data writers, and combinations thereof. A first subset of the elements is operable for reading or writing data in a first tape format. A second subset of the elements is operable for reading or writing data in a second tape format, at least some of the elements being present in both subsets. The elements are aligned laterally along a line transverse to the direction of travel of the magnetic medium over the head. A spacing of servo bands on a tape written in the first format is different than a spacing of servo bands on a tape written in the second format. 
   As mentioned above with reference to  FIG. 1 , a typical tape head includes two modules, each module having an array of data elements thereon for reading and/or writing data in a particular data format. The present invention includes a new two module head capable of reading and/or writing in two different data formats. One skilled in the art will also appreciate that the embodiments herein can also be expanded to heads having a single module (where, for example, the single module may be formed on a single substrate) and heads having more than two modules. The latter are described in more detail below. 
     FIG. 5  illustrates a tape bearing surface view of an exemplary module  500  having an array  502  of elements. In one approach, shown generally in  FIGS. 6-7 , a first subset of the elements is operable for reading and/or writing data in a first tape format, while a second subset of the elements is operable for reading and/or writing data in a second tape format, at least some of the elements being present in both subsets, and where the first and second data formats are different. The first and second subsets can also be thought of as first array of elements with a second array of elements interspersed therein, where the second array of elements and a subset of the first array of elements are associated with a second tape format. 
   Again, the elements can include readers, writers, or both. Depending on the format, the proper subset is aligned with a given data band in a conventional way, e.g., by servoing. 
   With continued reference to  FIG. 5 , the tape  510  is shown in dashed lines. While it is not typical to write data in two different formats on the same tape, the present embodiment would enable this feature, as described below. To illustrate different formats,  FIG. 5  shows data in the first and second formats overlapping. This is for illustration purposes, and one skilled in the art will appreciate that the data bands in the two formats would not typically be concurrently present on the same area of the tape. Data in the first format is associated with servo bands  512  and data bands (Band  0 - 3 ). Data in the second format is associated with servo bands  512  and  514 . The data bands  516  in the second format are significantly smaller and so are not individually identified alphanumerically. However, a representative data band  516  is shown in  FIG. 5  for illustrative purposes. 
   In one preferred embodiment, the head includes servo readers for reading servo bands on the tape, where a number of servo bands supported in each of the formats is one more than a number of data bands in the particular format. Thus, as shown in the example of  FIG. 5 , there are five servo bands  512  for the four data bands (Band  0 - 3 ) written in the first format, while there are thirteen servo bands  514  for the twelve data bands written in the second format. It follows that in some embodiments, a number of servo readers associated with the array  502  of elements is no more than two times the number of formats supported. 
   In another preferred embodiment, the spacing of the servo bands on the tape written in the first format is different than a spacing of servo bands on a tape written in the second format. 
   The second data format may be a new generation relative to the first data format. The first and second data format may also be formats used by competing vendors, used in different standards, etc. Typically, the differences between formats will include one or more of: differing servo band locations, differing written track width, differing track density per data band or tape width, differing track centerline-to-centerline spacing, differing element centerline-to-centerline spacing, etc. Accordingly, the subsets will have servo reader position, element spacing, element width, etc. that are designed to function in the format with which associated. 
   In one embodiment, the second format is a scaled-down version of the first format, especially in feature size. Accordingly, the second subset in such embodiment is a scaled-down version of the first subset. For example, the second subset may have the same number of data tracks per band, but is scaled down from the first subset, for example by a factor of about 3. In other words, the second subset is about 33.3% the width of the first subset. Thus, the format characteristics are also scaled down. For example, the track density on the tape could increase by approximately 3× in the second format as compared to the first format. If the linear data density also doubles, the tape capacity in the second format will be 6× the first format. 
   With continued reference to  FIG. 5 , both subsets of the array  502  may be formed in the same gap on the module  500  and the elements of the arrays are interspersed with each other generally in a direction transverse to the direction of media travel. 
   In operation, the tape drive system or host system can identify the format of the servo pattern on the tape and/or the format of the data on the tape using one of several techniques. One way to determine the format(s) is by reading a cartridge memory chip in the tape cartridge that identifies the format. Another way to identify the format is by reading a small portion of the data bands and matching, for example, the servo bands to a look up table (LUT). Note that all subsets may be active at this time, or the system may sequentially operate the subsets. In other embodiments, the user may indicate which format is used on the tape. Once the format is identified, the controller, host, or user selects the proper subset for reading and writing. The system energizes the subset associated with the identified format, such as by energizing the leads coupled to the desired subset. Now active, the desired subset is aligned with one of the data bands in a standard way, e.g., by servoing, and the tape is passed over the head for reading/writing. Preferably, either one subset or the other is energized at a time during standard read/write operations. 
   In one embodiment, the elements for both subsets are built simultaneously during thin film buildup. For instance, consider elements in a “piggyback” configuration. This type of element typically includes a reader formed on a substrate, with a writer formed thereon. The reader and writer may be positioned so that one of the reader shields also functions as a pole for the writer, known as a merged transducer configuration. During construction of a multi-format piggyback head, the readers of the first subset are formed concurrently with the readers of the second subset. Then the writers of the first subset are formed concurrently with the writers of the second subset. The readers of the first and second subsets may be aligned along a line transverse to the direction of media travel, and thus the writers of both subsets may also be aligned. Likewise, for an interleaved head, the readers for both subsets can all be formed during a single processing sequence, and the writers can be formed in another processing sequence. 
   The subsets can be slightly offset in a vertical direction for design considerations. For example, the upper shields for readers in the first subset may be formed concurrently with the lower shields for readers in the second subset. Then the readers in the second subset are completed in subsequent steps. Thus, in some embodiments, the elements are formed concurrently in the same processing sequence, though only some of the processing steps affect both subsets. 
   In further embodiments, the subsets can be formed by independent processing sequences. For example, one subset can be completed prior to forming the other subset. The subsets may be aligned in a direction transverse to the direction of tape motion, or can be displaced transverse to the direction of tape travel and offset in a direction parallel to the direction of tape travel. 
   Further, each subset can be formed on an individual module, where selected elements may be displaced relative to other elements in a direction parallel to the direction of tape travel. 
   Forming the various subsets concurrently reduces process steps over the contemplated methods described above, such as forming elements in tandem parallel to the tape travel direction or even placing R/W subsets for different formats on different modules. One skilled in the art will appreciate the advantages achieved by processing all of the elements concurrently, including lower cost, faster production time, reduced chance of error, etc. Write and read transducer magnetic gaps may be independently optimized for each format. 
   Because the subsets of elements are interspersed, the width of the head does not need to be significantly increased. Typically, the width of the head may be based on the smallest format to ensure that the tape bearing surface supports the entire tape at all possible positions. 
   One embodiment of the present invention is illustrated in  FIG. 6 , wherein two subsets  602 ,  604  of the array  502  are formed on a module  500 . As shown, the second subset  604  includes some elements of the first subset  602 . The number of elements in the first subset  602  may be the same as the number of elements in the second subset  604 , e.g., 8 and 8, 16 and 16, 24 and 24, 32 and 32, etc. In other embodiments, the number of elements in the first subset  602  is different than a number of elements in the second subset  604 , e.g., 8 and 16, 16 and 32, 16 and 8, 32 and 24, etc. While the number of elements in a given subset has been represented a multiple of a power of 2 (e.g., multiple of 8=2 3 ), the number of elements in the array and/or the various subsets may be any number. 
   In some approaches, the elements in the first and second subsets have the same construction, while in other approaches the elements in the each subset has a different construction. Further, non-dual-use elements may have different design(s) from dual-use elements. 
   In the embodiment of  FIG. 6 , the elements are positioned generally laterally adjacent each other along a line transverse to the direction of travel of the magnetic medium over the head. However, some of the elements may be offset or misaligned. 
   Preferred embodiments employ individual pairs of servo readers  606  for each format. In the latter case, as shown in  FIG. 5 , the spacing of servo bands  512  on a tape written in the first format is different than a spacing of servo bands  514  on a tape written in the second format. 
   In another approach, shown generally in  FIG. 7 , at least one element of the first array (first subset)  602  functions as a servo reader  606  for the second array (second subset)  604 . 
   The head as recited in claim  1 , further comprising servo readers associated with the array of elements, a number of the servo readers being no more than two times the number of formats. 
   In yet other embodiments, the first and second subsets  602 ,  604  can share one of the servo readers  606 . 
   In particularly preferred embodiments, it is generally preferred that there are no more than two servo readers for each supported format. Thus, where two formats are supported, there are preferably no more than four servo readers associated with an array of elements. However, more or less servo readers  606  may be present. 
   The following describes particularly preferred approaches. The spacing in the grid of one subset of elements (i.e., the transducer pitch or center-to-center distance) is an integer multiple (e.g., 3) (or an integer ratio [e.g., 3/2]) of the other(s). At least one member of each ‘progressive pair’ of subsets is common; i.e., one or more transducers are dual-use elements, used to write and/or read information in two (or more) formats. In this way, a reduced-span head is achieved which is also backward compatible. The element pitch reduction (e.g., integer multiple, say, 3) achieves the head span reduction (e.g., approximately 2×) and, optionally, an increase in the channel count (e.g., 1.5×). The element pitch reduction factor (e.g., 3×) is equal to an (approximate) head span reduction factor (e.g., 2×) times the channel count increase factor (e.g., 1.5×). Also, typically, the number of channels in the second format (e.g., 24)=the element pitch reduction factor (e.g., 3×) times the number of dual-use channels. 
   As an example, a first format array has a head element pitch of 166.5 μm across 16 channels, for a data transducer head span of 2497.5=(16-1)*166.5 μm. A second format has a head pitch of 55.5 μm across 24 channels, for a data transducer head span of 1276.5=(24−1)*55.5 μm. The element pitch reduction is 3×. The span reduction is approximately 2× (1.96). The channel count increase is 1.5×[3×=2×*1.5×]. In this example, the arrays (subsets) have the same centerline. There are a total of 32 data elements (data readers or data writers or data reader/writer pairs): 16=(8 dual-usage+8 first format only) are used simultaneously for the first format; 24=(8 dual-usage+16 second format only) are used simultaneously for the second format; 8 are dual-usage elements. (24 channels)=(8 dual-usage)*(3× element pitch reduction). Additionally, in this example, there are four (4) servo reader elements on each head module (2 each for each format). Two- or three-module heads could be formed into bidirectional write/read heads, having various appropriate combinations of data writer, data reader, and/or servo reader transducers. 
   This pair (or more) of merged arrays (subsets) may thus achieve a head compatible with both an ‘old’ format, and a ‘new’ format; wherein the ‘new’ format enables one or more of (1) track density and/or reader track width increases through head span reduction, (2) increased data rate and/or reduced tape speed enablement through an increased channel count, while (3) using a reduced element set (32 data elements in the above example instead of 40=16+24), minimizing the cost and complexity of each head module and its associated cable and, perhaps, the attached driving electronics, as well. 
   As mentioned above, one way to build a head is to have two modules, in a configuration similar to existing heads, e.g., the head of  FIG. 1 . One such embodiment is shown in  FIG. 8  illustrates a flat-lapped bi-directional, two-module magnetic tape head  1000 . As shown, the head includes a pair of bases  1002 , each equipped with a module  1004 . The bases may be conventional U-beams that are adhesively coupled together. Each module  1004  includes a substrate  1004 A and a closure  1004 B with an array  502  of elements situated therebetween. Cables  1010  connect the elements to a controller. The cables  1010  are shown as split into leads for the two formats, but can be joined, fused, intermixed, overlayed, etc. Note that, because the first and second subsets share elements, only one pair of leads need be coupled to the shared elements, thereby simplifying cabling. 
   In use, a tape  1008  is moved over the modules  1004  along the tape bearing surfaces  1009  thereof for reading and writing data on the tape  1008 . Depending on the format of the data or servo on the tape, or to be written to the tape, the subset of elements on each module corresponding to that format is activated and used to read and/or write to the tape. 
   Another way to build the head is to have the functions of reading and writing performed on different modules. As shown in the write-read-write (W-R-W) head  1100  of  FIG. 9 , outer writing modules  1102 ,  1104  flank a single reading module  1106 . As the names imply, the outer modules  1102 ,  1104  include one or more arrays of writers in a configuration, for example, as shown in  FIGS. 6-7 . The reading module  1106  includes one or more arrays of readers. The modules  1102 ,  1104 ,  1106  are offset and set in relationship with each other such that internal wrap angles are defined between the modules  1102 ,  1104 ,  1106 . Cables  1109  connect the elements to a controller. The cables  1109  are shown as split into leads for the two formats, but can be joined, fused, intermixed, overlayed, etc. 
   In this embodiment, the tape bearing surfaces of the modules lie on parallel planes, but are offset in a direction perpendicular to the planes. When the tape  1108  moves across the head  1100  as shown, air is skived from below the tape  1108  by a skiving edge  1110  of the first outer writing module  1102 , and instead of the tape  1108  lifting from the tape bearing surface  1112  of the first outer module  1102  (as intuitively it should), the reduced air pressure in the area between the tape  1108  and the tape bearing surface  1112  allow atmospheric pressure to urge the tape towards the tape bearing surface  1112 . The trailing end  1120  of the outer writing module  1102  (the end from which the tape leaves the outer writing module  1102 ) is the reference point which defines the wrap angle α o  over the tape bearing surface of the inner reading module  1106 . The same is true of the other outer writing module  1104  when the tape travel direction is reversed. 
   Variations on the head  1100  of  FIG. 9  include a R-W-R head, a R-R-W head, a W-W-R head, etc. For example, in a R-W-R head, the outer modules  1102 ,  1104  perform reading while the middle module  1106  performs writing. In a R-R-W head, the leading module  1102  and middle module  1106  perform reading while the trailing module  1104  performs writing. In a W-W-R head, the leading module  1102  and middle module  1106  perform writing while the trailing module  1104  performs reading. Again, the leading and trailing modules  1102 ,  1104  may operate concurrently with each other and the middle module  1106 , may operate individually, or may operate in combinations of two modules. 
   An advantage of the multiple module head is that each module has no more wiring leads than a module in a two module head having both read and write elements. For instance, assume a legacy format head has 16 readers and 16 writers per module. Adding an array of second format elements would add 32 more elements, or 64 more wires. However, if each module has only readers or writers, albeit in two formats, the number of wires per module is the same as the legacy read/write head. Accordingly, existing cabling can be used, the number of wires per head is minimized, etc. 
   Another advantage is that air is entrained between the tape and the trailing outer module ( 1104  in  FIG. 9 ), thereby reducing wear. 
   The three module design is also preferred, as the total gap thicknesses and build complexity are minimized, and head yield is optimized. 
   The invention is not limited to flat profile heads; heads having rounded and other geometric tape bearing surfaces are also within the spirit and scope of the present invention. 
   In any of the embodiments described herein, the heads can be fabricated in conventional ways. To reduce cost and complexity, one lead for an element of the first array may be commoned with one lead for an element of the second array (and so on for additional arrays) to minimize head wiring, an on-going goal in head design. 
     FIG. 10  illustrates a simplified tape drive system  1200  according to one embodiment of the present invention. While one specific implementation of a tape drive  1200  is shown in  FIG. 10 , it should be noted that various embodiments presented herein may be implemented in the context of any type of tape drive system. 
   As shown, a tape supply cartridge  1220  and a take-up reel  1221  are provided to support a tape  1222 . These may form part of a removable cassette and are not necessarily part of the system  1200 . 
   Guides  1221  guide the tape  1222  across a preferably bidirectional tape head  1226 . An actuator  1232  controls position of the head  1226  relative to the tape  1222 . The tape head  1226  is in turn coupled to a controller assembly  1228  via a connector cable  1230 . The controller  1228 , in turn, controls head functions such as servo following, write functions and read functions, etc. The controller  1228  runs under the control of computer instructions typically in firmware or software run locally or on a host system. 
   The tape drive  1200  may further include drive motor(s)  1224  to drive the tape supply cartridge  1220  and the take-up reel  1221  to move the tape  1222  over the head  1226 . An interface may also be provided for communication between the tape drive and a host (integral or external) to send and receive the data and for controlling the operation of the tape drive and communicating the status of the tape drive to the host, all as will be understood by those of skill in the art. Examples of a host system include a computer or other processor-based system or network, etc. in communication with the tape drive  1200 . 
   In another embodiment, the tape drive system is part of a larger library of tape drive systems that provide coordinated data backup using several drives. 
   While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.