Abstract:
A method and apparatus for placing and later determining the distance between transitions from a first logical state to a second logical state stored on a medium, for example, a document. This determination is used to precisely characterize the information pattern in order to authenticate the information and the medium on which the information is stored. The invention uses a reader having a leading and trailing read apparatus, which allow information to be read simultaneously from two or more locations spaced a known distance apart. The distance between the center lines of each read apparatus is preferably an odd integer multiple of one half the distance between logical clock transitions. The distance between a first transition at the leading read apparatus and a next transition at the trailing read apparatus is used as a reference, hence given the term the “Reference Value”. The Reference Value is compared with the distance between the first transition and a second transition on the medium. Detection of deviations in spacing between transitions is unaffected by variations if the velocity of the medium with respect to the reader. Thus, the present invention is a method and apparatus for reading and writing conventional ISO 7816 data with additional precisely placed pulses that appear as noise to conventional reading apparatuses and as data to the described invention. In addition the present invention applies to a medium, which moves at an uncontrolled velocity relative to a read/write apparatus with which the data is read and written.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a new and improved device for reading, modifying and writing information on a storage medium, and more particularly to a method and apparatus for authenticating the medium and information stored on the medium by performing spatial measurements using a divided track transducer head. 
     2. Description of the Related Art 
     In many instances, it is desirable to provide a method and apparatus for storing and transporting information. In particular, many ways have been devised for encoding information on a medium which can be conveniently carried about by a person during the normal course of business. For example, credit cards, debit cards, electronic purse cards, decrementing value cards, checks, driver&#39;s licenses, identification cards, access control cards, magnetic tapes and disc, and many other such media which are small enough to be conveniently carried in a person&#39;s handbag or wallet are ubiquitous today. However, in many of the applications in which these media are intended to be used, security is an important concern. That is, it is important that only authorized organizations are capable of modifying the information stored thereon. One very common way for information to be stored on such a medium is by magnetically encoding the information. 
     Techniques for encoding information on magnetic media have been available for many years and are now relatively inexpensive. Other techniques include optical storage techniques and printed information using relative light and dark areas, such as the uniform purchasing codes (UPCs) which are printed on the packaging of most products today. For simplicity sake, only magnetic techniques are discussed in detail. However, it will be understood that the following discussion applies equally well to other techniques for storing information. 
     Cards which have a magnetic stripe attached thereto are ubiquitous in modem society. That is, nearly everyone carries one of the following cards, each of which typically has a magnetic stripe attached thereto: credit cards, bank cards (ATM cards), debit cards, identification cards, driver&#39;s licenses, security access cards, check cashing cards, etc. Data is typically represented on magnetic medium by polarizing magnetic particles of the magnetic medium in one of two magnetic states. When magnetic medium is swiped across an inductive read head the moving magnetic field induces a magnetic field in the head core structure which in turn induces an electric current in the head read coil. 
     Alternately the change in magnetic field states can be directly measured using a magnastritive (MR) head. Either voltage waveform is converted to pulses with a peak detector. When reading the data from the magnetic medium, transitions between the two magnetic field states induce a voltage in the magnetic head read coil. A peak detector circuit translates this voltage into binary states. The head coil voltage is amplified by a differential amplifier then a dual edge peak detector switches between ground and VCC states each time the input changes polarity. The output of the peak detector is buffered by comparator with hysteresis to improve noise immunity. The states generated are detected as pulse durations; one pulse duration is approximately double in length to the other. The longer pulse duration represents a bit cell time and data value of zero, two consecutive pulse of the shorter duration also represent bit cell and in this case a data bit value of one. 
     Magnetically encoded information can easily be copied or transferred from one magnetic information storage medium to another. Unless special provisions are made to secure the information, information can be altered and re-encoded back onto the original medium or a duplicate of the original medium. If the information is used in a system for organizing financial transactions or for personal identification, then such copying, altering, and duplicating makes the person for whom the information was intended, and the organization who operates the system, vulnerable to fraud. 
     For example, if a magnetic stripe affixed to a debit card is used to indicate how much money is currently in a personal account, modifications to that information can be used to increase the apparent balance in order to purchase goods which have a higher value than actually exists in the account. Additionally, if the card is duplicated, the same account could be used by more than one person. It should be clear that fraud could occur in a number of ways if sensitive information is not properly secured. In fact fraud due to copying and modification of information magnetically encoded on portable media, such as magnetic stripe cards, is growing at an alarming rate. For example, it is estimated that the cost of fraud to the credit card industry alone will exceed one billion dollars per year before the end of the century. 
     A number of techniques have been proposed to authenticate both the information, and the medium on which the information is stored (commonly referred to as a “document”), in order to prevent fraud. For example, U.S. Pat. No. 4,023,204 issued to Lee, discloses using a unique magnetic coating with pre-determined alignment of the magnetic particles as the basis for authentication measurements. Thus, a code which can not be altered can be implanted into the document to authenticate the document. U.S. Pat. No. 5,336,871 issued to Colgate, discloses the use of a hologram to authenticate a substrate on which a magnetic stripe is affixed. U.S. Pat. No. 5,354,097 issued to Tel, discloses the use of overlays to authenticate information. 
     U.S. Pat. No. 4,628,195, issued to Baus, discloses generating a security code number determined by the relative spatial positions of corresponding data in two different forms of encoded data on a card. In particular, Baus discloses using a conventional magnetic stripe as the first means for encoding data, and using embossed characters as a second means for encoding data. The relative position of the magnetic information with respect to the embossed information is used ti) generate a numeric security code. In addition, dyes or absorbers incorporated in a magnetic stripe have been used to attempt to encode a security identifier into the document on which the information resides. 
     However, each of these methods requires the use of special materials in the security process. Accordingly, none of the old documents would be usable, and all of the documents currently in use would have to he recalled and reissued using the new security process. Recalling and replacing all of the documents that are currently in use would be very costly and has hampered the widespread implementation of such technologies. 
     In the case of the technique disclosed by Baus, both an automatic reading method for reading the magnetic stripe, and also an automatic reading method for reading the embossed characters, are required. Therefore, there are two sub-systems required by this technique. Furthermore, readers used at the point-of-sale must preserve the spatial relationship between the magnetically stored information and the embossed characters. This is a cumbersome and expensive process which is very difficult to perform at the point-of-sale. Accordingly, it may be difficult to maintain reliable operation of systems which conform to the Baus technique. 
     Others have attempted to overcome the above limitations when the document is a magnetic medium by employing characteristics of the magnetic signals used to store the information to authenticate both the document and the information stored thereon. For example, U.S. Pat. No. 4,837,426 issued to Pease, discloses a method for authenticating documents by analyzing the amplitude of the magnetic signals. U.S. Pat. Nos. 5,408,505 and 5,428,683, each issued to Indeck, et al. disclose a method for authenticating documents using “noise” in the saturation region of the magnetic data. U.S. Pat. Nos. 5,235,166, and 5,430,279, each issued to Fernandez, and U.S. Pat. No. 5,254,843 issued to Hynes, each disclose a method of authenticating documents by deriving inherent temporal measurements of timing variations of the data in the reading process. 
     All of the above mentioned methods for authenticating documents and information using characteristics of the magnetic signals have a common drawback in that variations in the motion of the document through the reading device cause variations in the characteristics used to authenticate the document, and therefore, result in errors in the authentication process. Furthermore, degradation of the reading device and the document over time due to natural wear causes the characteristics to either change, or to appear to change, causing further errors in the authentication process. 
     Accordingly, it would be desirable to provide a system which: (1) is capable of authenticating documents and the information stored thereon without use of a new material or process for generating the document to be authenticated; (2) is unaffected by changes in the speed at which the document moves with respect to the reader; and (3) will remain reliable over time. 
     In addition to the problems associated with authenticating documents and the information that is stored thereon, there is a need for methods for increasing the amount of information that can be stored on a document. For example, a magnetic stripe of a credit card is a relatively small area on which information can be stored. Accordingly, it would be advantageous to provide a method land apparatus which increases the amount of information that can be stored on a document. 
     Still further, in order to maintain standards for writing information on documents, it would be advantageous to be able to accurately determine the absolute distance between a transition in the information stored on a document from a first logical state to a second logical state without the need to control the velocity of the reader with respect to the document. The conventional method to accomplish this is with a precision peak detector which optimizes the peak detecting capabilities of conventional peak detector and using a constant speed drive transport. 
     Another method to accomplish this, as described in U.S. Pat. No. 5,770,846 issued to Mos et al., is with the use of a multiple gap magnetic head which detects adjacent bit transitions simultaneously. This method removes the requirement of a constant speed transport and still requires the use of precision peak detectors. 
     A new method of determining the placement of the data transitions without a peak detector is by measuring the frequency components of each bit cell with a Fourier or related transform. With this method of detection if two major frequency components occur, at F and ½ F the cell represents a data bit value of one. If only a single component is present at the lower frequency a cell data value of zero is decoded. The frequency components can be converted back to the time domain to accurately measure the distance between the points of interest. 
     With conventional magnetic stripe decoding there can be up to 14% variation in the ideal placement and actual detection of the bit-to-bit magnetic transitions. This variation along with the inability to sense an adjacent bit transition while writing data requires that conventional data writing write the complete track of information. When modifying data accurately measuring the placement is required to insure that the combined inaccuracies of the modified transitions and the initial placement is still within the 14% specification. 
     In U.S. Pat. No. 5,780,828 issued to Mos et al., there is described a method to selectively modify data without the requirement of writing a complete track of data. The method involves a two gap magnetic read head separated a know distance from a magnetic write gap. With the multiple read gaps separated by an odd multiple of bit transition spacing a write clock synchronized to the data can be generated. 
     SUMMARY OF THE INVENTION 
     This invention is a method and apparatus for reading and writing conventional ISO 7816 data with additional precisely placed pulses that appear as noise to conventional reading apparatuses and as data to the described invention using a combined spatial read/write head with a self-clocking data pattern, such as the Aiken code. In accordance with this invention, the velocity of the write head need not be constant with respect to the medium during the write operation. A write clock is generated by off setting two read heads by a known distance and using an integral write head to selectively modify the data. 
     Accordingly, a write clock can be generated from data, which is already present on the medium. Furthermore, by employing the split head spatial read/write head the data can be made secure from various sources of duplication including skimming. These observations are embodied in this invention as described below. 
     A number of embodiments of this invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Still further, it should be understood that while this invention is described in the context of a magnetic medium and magnetic read and write heads, this invention is applicable to any means for reading and writing data in which an Aiken code may be used. For example, such means might be bar codes written on paper, optically encoded data, etc. In yet another alternative embodiment of this invention, the read and write heads might move with respect to the medium. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the spirit and scope of the appended claims. 
     Therefore, the principal object of the present invention is to provide a new and improved method of encoding data on a medium. 
     It is a further object of the present invention to provide a new and improved method of reading data on a medium. 
     It is further object of the present invention is to provide new and improved method of securely encoding data on a medium compatible with conventional readers for non secured data. 
     It is a further object of the present invention to provide new and improved method of securely encoding data on a medium incompatible with conventional readers. 
     It is a further object of the present invention to provide a combination of functions of the above invention to provide greater utility than the individual functions support. 
     It is a final object of the present invention to improve and expand the capabilities of the conventional apparatuses used for reading and writing ISO 7816 data. 
     Briefly, the value-added data access that is the subject matter of the instant invention as described herein more specifically addresses a method and apparatus for placing and later determining the distance between transitions from a first logical state to a second logical state stored on a medium, for example, a document. This determination is used to precisely characterize the information pattern in order to authenticate the information and the medium on which the information is stored. The invention uses a reader having a leading and trailing read apparatus, which allow information to be read simultaneously from two or more locations spaced a known distance apart. The distance between the center lines of each read apparatus is preferably an odd integer multiple of one half the distance between logical clock transitions. The distance between a first transition at the leading read apparatus and a next transition at the trailing read apparatus is used as a reference, hence given the term the “Reference Value”. The Reference Value is compared with the distance between the first transition and a second transition on the medium. Detection of deviations in spacing between transitions is unaffected by variations in the velocity of the medium with respect to the reader. 
     Therefore, the present invention is a method and apparatus for reading and writing conventional ISO 7816 data with additional precisely placed pulses that appear as noise to conventional reading apparatuses and as data to the described invention. In addition the present invention applies to a medium, which moves at an uncontrolled velocity relative to a read/write apparatus with which the data is read and written. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above mentioned and other objects and features of this invention and the manner of attaining them will become apparent, and the invention itself will be best understood, by reference to the following description of the embodiment of the invention in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a prior art graphic representation of the voltage output from a read head, the output of the peak detector, the encoded data bit cell boundaries, and the decoded data for a magnetic medium. 
     FIG. 2 is an illustration of the prior art magnetic head structure; 
     FIG. 3 is a schematic diagram of a read apparatus dual peak detector; 
     FIG. 4 is an illustration of the improved spatial read/write apparatus magnetic head; 
     FIG. 5 is a graphic representation of the timing waveforms for fourth embodiment of this invention; 
     FIG. 6A is a timing diagram for the first alternate embodiment of this invention; 
     FIG. 6B is a illustration of the head structure for the first alternate embodiment of this invention; 
     FIG. 7A is an illustration of a divided track transducer for the third alternate embodiment of this invention; 
     FIG. 7B is an illustration of a magnet medium for the third alternate embodiment of this invention; 
     FIG. 8A is a graphic representation of the divided track transducer; 
     FIG. 8B is a graphic representation of a conventional transducer output for a magnetic medium encoded with a divided track transducer; 
     FIG. 9 is a graphic representation of the output waveform for the embodiments; 
     FIG. 10 is an illustration of a comparison of a conventional encoded data on the magnetic medium to the split head apparatus described in this invention; 
     FIG. 11 is an illustration of the embodiment of the invention; 
     FIG. 12 is an illustration of a “split gap” read/write apparatus; and 
     FIG. 13 is an illustration of the core construction of a “split gap” read/write apparatus. (head structure not core). 
     FIG. 14A is an illustration of a rear perspective exploded view of a secure split track read/write head structure having a integrated circuit mounting and termination board and an integrated circuit for attachment thereto; 
     FIG. 14B is an illustration of a front perspective exploded view of a secure split track read/write head structure having a integrated circuit mounting and termination board and an integrated circuit for attachment thereto; 
     FIG. 14C is an illustration of a front elevational view of a secure split track read/write head structure having both a spacial read/write head and a split track read write head; and 
     FIG. 14D is an illustration of a plan exploded view of a secure split track read/write head structure having a integrated circuit mounting and termination board and an integrated circuit for attachment thereto. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Throughout this description, the embodiment and examples shown should be considered as exemplars, rather than limitations on this invention. 
     Referring now to the figures, FIG. 1 is a prior art graphic representation of the voltage output from a read head  10 , voltage waveform  11 , the output of the peak detector  12 , bit cell time (zero)  13 , the data value of zero  14 , the data value of one  15 , the binary data stream  16  and the bit cell time (one)  17 . The change in magnetic field states can be directly measured using a magnastritive (MR) head. Either voltage waveform  11  is converted to pulses using a peak detector (described below, see FIG.  3 ). The state generated are detected as pulse durations; one pulse duration is approximately double in length to the other. The longer pulse duration represents a bit cell time (zero)  13  and data value of zero  14 , two consecutive pulses of the shorter duration also represent bit cells time (one) and data value of one  15  and in the aggregate a data bit value of zeros and ones, the binary bit stream  16 . 
     FIG. 2 is an illustration of the prior art magnetic head structure  20  comprised of a core head structure  21  and a head read/write coil  22 . When magnetic medium is swiped across an inductive read head, such as magnetic head structure  20 , the moving magnetic field induces a magnetic field in the head core structure  21  which in turn induces an electric current in the head read/write coil  22 . When reading the data from the magnetic medium, transitions between the two magnetic field states induce a voltage in the magnetic head read/write coil  22 . 
     FIG. 3 is a schematic diagram of a conventional read apparatus dual peak detector  30  with a head coil voltage read apparatus  31 , a differential amplifier  32 , the dual edge peak detector  33  and a comparator/output buffer  34 . The peak detector circuit  30  translates this voltage into binary states. The voltage from the head coil  31  is amplified by a differential amplifier  32  then a dual edge peak detector  33  switches between ground and VCC states each time the input changes polarity. The output of peak detector  30  is buffered by comparator  34  with hysteresis to improve noise immunity. 
     Referring now to FIG. 4, in the preferred embodiment of this invention the improved special read/write magnetic head apparatus  40  comprises an unconventional spatial read head where two read/write head magnetic components  40 A and  40 B, read head structure  41 , read head structure  43 , read coil  42  and read coil  44  share a common center return bar  45 , in which the centers return bar  45  is also a write head with center write coil  46 . The first read/write head magnetic component  40 A is spaced apart from the center return bar  45  by the leading read/write gap  47  and the second read/write head magnetic component  40 B is spaced apart from the center return bar  45  by the trailing read/write gap  48  and each are set in one embodiment to a multiple of three quarters of a bit cell. 
     The two read/write head magnetite components  40 A and  40 B read preexisting data from the medium offset by the multiple of three quarters of a bit cells indicated by the preexisting data bit cell read  51  and  52  illustrated in FIG.  5 . The write circuit generates a fast pulse write clock which is used to selectively write a pulse at the ¾ wavelength point as in the fast pulse write clock bit times  53  relative to the first or pre-existing data bit cell read  51 . The read cell bit times are shown in FIG. 5 as the leading head read cell bit times  54 , and the trailing head read cell bit times  55 . The write pulse creates a short transition at the point of the bit cell that is normally ignored by read apparatuses since it is not at a valid bit position. 
     In addition since the write head is only pulsed, no transition is created in the bit cell. Using the same improved special read/write magnetic head apparatus  40 , the pulse data can be recovered while the recovered data/existing data combined  56  is read. Due to the shortness of the pulse, conventional readers will not detect the pulse or if they do, they will discard the pulse as noise. 
     This improved special read/write magnetic head apparatus  40  can also be used to record conventional data. In this application, the leading read/write head magnetic components  40 A is used with a motorized or optical transport or cross track clock generation, (see U.S. Pat. No. 5,780,828 issued to Mos et al.) to generate the initial bit cell spacing information, which is similar to formatting other magnetic media. During format and conventional write operations the leading read/write gap  47  will write bit cell transition data that will be overwritten by the trailing read/write head magnetic component  40 B with a transition of the opposite polarity. Since the two read/write gaps  47  and  48  share a common center core each writes with an opposite polarity. In over-writing old data all transitions require the media to go though a polarity or state change. This allows the data to be placed with less variables and thus with greater accuracy. 
     In accordance with a first alternate embodiment of this special read/write magnetic head apparatus  60 , there is illustrated in FIG. 6A, how the magnetic encoded data  61  is converted to a voltage waveform  62  in the head structure and timing diagram  60  in FIG.  6 B. This device uses conventional spatial read/write heads where a read/write head magnetic component  60 A comprising a trailing head coil  63 , and a trailing head structure  67  and where a read/write head magnetic component  60 -B comprises a leading head coil  64 , and a leading head structure  68 , further comprising a trailing head read/write gap  65  and the leading head read/write gap  66 . 
     The trailing head read/write gap  65  and the leading head read/write gap  66  share a common center return bar  69  with a center write coil  69 A, having the trailing head read/write gap  65  and the leading head read/write gap  66  spacing as an odd multiple of one half bit cell. This embodiment optionally allows a special read/write magnetic head apparatus  60  to be used to write conventional data as in the previous embodiment. 
     In addition to decoding data the spatial read/write head can be used to measure the distance between transitions close to the spacing of the gaps. This spacing information can be used in security applications to prevent card modification and duplication. (see Mos et al. U.S. Pat. No. 5,770,846 and Mos et al. U.S. Pat. No. 6,260,146 B1). Since this embodiment can measure the distance over multiple transitions in the trailing head ready/write gap  65  and the leading head read/write gap  66 , the measurement is not jitter, which is the bit-to-bit variation in transition placement. 
     In accordance with a second alternate embodiment of this special read/write magnetic head apparatus as shown in FIG. 6A, the magnetic encoded data  61  is converted to a voltage waveform  62  illustrated in FIG. 6B, using a conventional spatial read head where a read/write head magnetic component  60 A comprising trailing head coil  63 , and trailing head structure  67  and leading head coil  64 , and leading head structure  68 , with trailing head read/write gap  65  and the leading head read/write gap  66 , sharing a common center return bar  69  with center write coil  69  in which the center return bar  69  may also be used as a write head with two return bars comprised of the two read/write heads magnetic components  60 -A and  60 -B with the gaps between the heads being a known distance. 
     The distance in one case is chosen to be close to an odd multiple of one half a bit cell. With the distance slightly less than the odd multiple described in first alternate embodiment the transition-to-transition spacing measurement always generates a positive number, which has advantage in many systems. In addition the special read/write magnetic head apparatus as shown in FIG. 6A can be used with a short pulse as described in the preferred embodiment. In this case a short pulse is placed adjacent to a data transition. A similarly constructed head can detect this pulse, while a conventional read device will not detect the pulse. 
     In accordance with a third alternate embodiment of this special read/write magnetic head apparatus as shown in FIG. 7A, the magnetic encoded data  61  is converted to a voltage waveform  62  as shown in FIG. 6 using a divided track transducer head  70  illustrated in FIG.  7 A. With this device a read/write head magnetic component  70 -A consisting of trailing head coil  76 , and trailing head structure  73  and read/write head magnetic component  70 -B consisting of leading head coil  77 , and leading head structure  74 , with trailing head read/write gap  75  and the leading head read/write gap  78 , share a common center return bar  79 , as similarly described in the improved special read/write magnetic head apparatus  40 . In addition the head core is composed of laminations that are constructed of materials that are both ferrous and non-ferrous further illustrated in FIG.  13 . 
     The effect is to allow the leading head read/write gap  78 -A to write leading head read/write gap data  78 -B as illustrated in FIG. 7B on the magnetic medium  71  over a portion of the track  72 -A and the trailing head read/write gap  75 -A to write trailing head read/write gap data  75 -B over a different portion of the track  72 -B. Conventional data is further illustrated in FIG. 10 where a magnetic medium  101  carrying normal track data is compared with a magnetic medium carrying  102  carrying split head data. Using spatial read/write magnetic head apparatus as shown in FIG. 7A causes data transitions to be comprised of multiple transition segments separated by the spacing of the read/write head gaps  75 -B and  78 -B in the axis of the data. 
     During a subsequent read operation illustrated in FIGS. 8A and 8B, FIG. 8A displays a similar split head structure  81  where the leading and trailing read apparatus outputs  82 ,  83  and  84  are synchronized with each other allowing the data to be recovered. Since the data transitions illustrated in FIG. 8B are offset and made up of two or more segments a conventional read apparatus or “skimmer” using conventional heads  85 , will detect data  86 ,  87  and  88  as garbled and unreadable. This embodiment, read/write magnetic head apparatus as shown in FIG. 7A addresses the problem of skimming as discussed above. 
     FIG. 9 illustrates the third alternate embodiment, spatial read/write magnetic head apparatus as shown in FIG. A, in which the spatial variations from each of the read heads are used to verify the data authenticity. Since the split head writes two of more transitions simultaneously offset in both the X and Y split head write data waveform directions  92 ,  93  and  94 , and since various variations in the magnetic recording process such as material and head spacing cause the recorded transitions to vary in placement from the ideal  95 , (see Mos et al. U.S. Pat. No. 5,770,846 and Mos et al. U.S. Pat. No. 6,260,146 B1), the deviation from coincidence on read data from the multiple read heads can be used to generate a signature for the data that can be used to verify that the card is the original and not a copy. 
     In accordance with the third alternate embodiment, special read/write magnetic head apparatus as shown in FIG. 7A, if the Precision Peak Detector is replaced with a Digital Signal Processor capable of performing the function of the Precision Peak Detector, performing a Fourier transform on each bit cell, the frequency can be ascertained directly from the digitized analog data without the need of peak detection. The frequency data can be used to decode the data and the frequency deviation between the multiple read heads can be used to generate the signature information. The signature information from the split head of the third alternate embodiment of the special read/write magnetic head apparatus as shown in FIG. 7A is added to the previously recorded data of the same or alternate track using any of the spatial write pulse techniques described. 
     Multiple track heads may be constructed from variations of the heads described in the previous embodiments with each track being used to address a different requirement for a given system. 
     In accordance with a fourth alternate embodiment of this invention, in a split track spatial read/write head  40 - 5  one or both of the read head coils  115  and  116  are augmented with secondary write coils  113  and  114  illustrated in FIG.  11 . This allows for a bucking voltage to be applied selectively to either core, which lowers the magnetic field strength to a level below that which is required to affect the magnetic domains on the media allowing each ½ track of data to be independently controlled. In addition to increasing the amount of data that can be stored on the track the data can be configured so that a conventional reader can decode standard ISO data and a reader using the split track spatial read/write head  40 - 5  can decode both ISO data and additional data to be used for security or other applications. 
     In accordance with the fifth alternate embodiment of this inventions a split track spatial read/write head  40 - 6  will have the addition of a secure semiconductor device  141  mounted on the terminal board  143  illustrated in FIG. 14 to provide for security against tampering including and not limited to a serial number, manufacturing test parameters such as actual gap spacing, a temperature sensor, an encryption engine for secure communication with a controller, and a serial communication controller for communicating with a host controller. One or more of the above functions may be combined into a single integrated circuit  142 . 
     FIG. 12 is an illustration of the fifth alternate embodiment of this invention, a split track spatial read/write head  40 - 6  comprising ferrous and non-ferrous structures displaying the relative locations of two read/write gaps  121 -A and  121 -B and two read/write gaps  122 -A and  122 -B formed within a read/write apparatus in accordance with one of the embodiments of this invention. As is well known in the art of reading and writing data on a magnetic medium, a magnetic field is generated across a gap in the magnetic core material of a write head. 
     The magnetic field is typically generated by applying a current through write coil  127  wound around the magnetic center return bar  126 . In this case the write core material is the center return bar 126  of the split track spatial read/write head  40 - 6 . The core made of non-ferrous material  124  and the core made of ferrous material  125  which also form the read head structure complete the magnetic path for the write circuit. The field that is generated is sufficiently strong to polarize magnetically sensitive particles at the surface of a magnetic medium over which both gaps of the write head passes. When a read head passes over the magnetically polarized particles of the medium, changes (commonly referred to as “transitions”) in the magnetic field generate a current in a coil wound around a magnetic core material of the read head. 
     In accordance with the fifth embodiment of this invention, two such read/write gaps  121 -A,  121 -B and two such read/write gaps  122 -A,  122 -B illustrated in FIG. 12 are provided. The spacing between the longitudinal center lines of the read/write gaps  121 -A,  121 -B,  122 -A and  122 -B is preferably a known distance. In addition the cores  123  and  128  are comprised of a stack of both ferrous and non-ferrous materials  132 ,  133  and  136  to create the split gap effect further illustrated in FIGS. 13A,  13 B and  13 C. Non-ferrous cores  131 , 134  and  135  are also depicted in the split gap core construction  130  shown in FIGS. 13A,  13 B and  13 C. 
     Bit cells  13  depicted in FIG. 1, prior art, are defined as the predetermined distance between clock transitions, when the data is written in a particular self-clocking code, such as Aiken code, in which a data transition occurring halfway between such clock transitions indicates a first logic state  17 , and in which no transitions occurring between clock transitions  13  indicates a second logic state. 
     It should be noted that the waveforms  51 ,  52  shown in FIG. 5 are not the waveforms that are directly output from the read heads, but rather are those waveforms which appear at the output of a wave shaping circuit in FIG. 3 which causes a square wave to be output. The output has transitions from a high state to a low state or from a low state to a high state occurring each time a read head detects a transition from one polarity to the other. 
     In the present description with relation to the graphic representation in FIG. 5, the read heads generating outputs  51 ,  53  are assumed to include all necessary circuitry to output such signals, including amplifiers and wave shaping circuitry. The output  51  is from the leading read head, which includes the read/write gap  121 , and the output  52  is from the trailing read head, which includes read/write gaps  122 -A and  122 -B. It can be seen that the data is written as two distinct transitions  121 -A and  121 -B shown in FIG. 12B separated by the spacing of the read/write gaps  126 -A and  126 -B. It can also be seen that since both transitions are written by the same write current that the spacing of the correspondingly written pulse is controlled by the spacing of the gaps and the variations in the magnetic characteristics of the medium. 
     During subsequent reading of these transitions the timing differences  95  depicted in FIG. 9, can be used to generate a signature based on deviation from ideal transition placement, which is then stored to verify the authenticity of the data. Other systems which uses spacing deviations of the magnetic transitions to secure data are hampered by either or both the timing inaccuracies caused by the read or write mechanism. This is caused by the need to move the medium from the position of the first to second transition. 
     In a sixth alternate embodiment of this invention, the spacing between the longitudinal center lines of the read/write gaps  121 -A,  121 -B,  122 -A and  122 -B is preferably an odd multiple of one half the bit cell distance (e.g., ½, 1½, 2½ . . . ). In addition to the center return bar  117  each read/write head magnetic component  111  and  112  also includes a write coil  115 , 116  illustrated in FIG.  11 . 
     By selectively enabling a bucking current at either read/write head magnetic component  111  and  112  the magnetic strength though that path can be reduced to below the level required to cause a magnetic transition to be written. As in the previous embodiment data is written and a security signature is written. In addition the data is selectively modified using bucking coils to include the security signature with the secure data. 
     It should be understood, however, that even though these numerous characteristics and advantages of the invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, interactivity and arrangement of components within the principal of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.