Abstract:
An asperity data storage system wherein asperities are used to represent stored data. The asperity data storage system includes an asperity transducer that thermally interacts with a data storage medium adapted to store an information-encoded pattern of asperities thereon, such as a rotatable disk, a streamable tape, or a fixed medium. A drive system produces relative motion between the data storage medium and the asperity transducer, while electrical signals corresponding to the asperities are processed as stored information. A positional relationship can be maintained between the asperity transducer and the data storage medium using the asperities on the data storage medium for reference. A related asperity data storage method and the asperity data storage medium itself are further disclosed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to data storage systems, such as disk drives, tape drives and the like. More particularly, the invention is directed to a new form of data storage system that does not rely on magnetic, optical or magneto-optical means to store and retrieve information.  
         [0003]     2. Description of the Prior Art  
         [0004]     By way of background, data storage systems such as disk drives and tape drives conventionally implement magnetic, optical or magneto-optical recording and playback techniques to store and retrieve information on a passive storage medium. Magnetic storage devices utilize magnetic domains on a magnetic storage medium to represent stored data. During data readback operations, a magneto-resistive read head senses changes in the magnetic moments of the magnetic domains and generates a readback signal corresponding to the recorded information. Optical storage devices utilize pits formed on an optical storage medium to represent stored data. During data readback operations, an optical read head directs a laser light beam onto the storage medium. When the pits are encountered, the phase of the reflected light changes and produces a readback signal corresponding to the recorded information. Magneto-optical storage devices utilize perpendicularly oriented magnetic domains on a magneto-optical storage medium to represent stored data. During data readback operations, a read head directs a laser light beam onto the storage medium. The magnetic domains on the medium rotate the polarization vector of the incident light beam upon reflection, thus producing a readback signal corresponding to the recorded information.  
         [0005]     It is to new techniques for storing information that the present invention is directed. In particular, instead of employing conventional magnetic, optical and magneto-optical storage methods as described above, a data recording and playback system that relies on head-media physical (including contact) interactions is considered for use in a data storage system.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention presents an asperity data storage system (having read and/or write components), a method and a medium wherein asperities are used to represent stored data. In accordance with one aspect of the invention, an asperity data storage system includes an asperity transducer for thermally interacting with a data storage medium adapted to store an information-encoded pattern of asperities thereon. A drive system produces relative motion between the data storage medium and the asperity transducer by moving the data storage medium relative to the asperity transducer or visa versa. Channel circuitry processes electrical signals corresponding to the asperities as stored information. The foregoing system can be implemented to operate with either a removable data storage medium or a non-removable data storage medium constructed as part of the system. Transducer positioning circuitry can be provided to control a positional relationship between the asperity transducer and the data storage medium using the asperities on the data storage medium for reference.  
         [0007]     The asperity data storage system of the invention can be implemented as a data retrieval system, with the asperity transducer comprising an asperity reader. In an exemplary construction, the asperity reader can be fabricated as a thin-film structure having a substrate layer, a first insulative layer on the substrate layer, a sensor layer on the first insulative layer, a second insulative layer on the sensor layer, and a closure layer on said second insulative layer.  
         [0008]     The asperity data storage system of the invention can also be implemented as a data recording system, with the asperity transducer comprising an asperity writer. In an exemplary construction, the asperity writer can be fabricated as one of a laser writer, an imprinting writer, a laser print head writer, and an ink jet print head writer. The foregoing may be adapted to operate on a nano-scale, such that high density asperities are formed using techniques such as nano-imprinting, nano-indenting, nano-particle deposition, etc.  
         [0009]     The asperity transducer can be constructed as a combined asperity reader and an asperity writer, such that the asperity data storage system functions as both a data retrieval and recording system.  
         [0010]     In further exemplary constructions, the data storage system of the invention can be implemented as an asperity disk drive in which the data storage medium comprises a rotatable disk and the asperity transducer is mounted on a slider carried by an actuator arm. Alternatively, the asperity data storage system of the invention can be implemented as an asperity tape drive in which the data storage medium comprises a streamable tape and the asperity transducer is mounted on a tape head or on a helical scanning drum.  
         [0011]     In accordance with another aspect of the invention, an asperity data storage method is provided in which an information-encoded pattern of asperities on a data storage medium is used to represent stored information, and thermal interactions with the asperities are used to transduce the information. In accordance with this method, asperities on the data storage medium may further be used as a reference for maintaining a positional relationship between an asperity transducer and the data storage medium. The foregoing method can be used to implement a data retrieval operation wherein the asperity pattern is read from the data storage medium. The method can also be used to implement a data recording operation wherein the asperity pattern is written to the data storage medium. The storage medium could be a rotatable disk, a streamable tape, or a fixed medium.  
         [0012]     In accordance with a further aspect of the invention, a data storage medium is provided in which an information-encoded pattern of asperities is used to represent stored information. The asperities are constructed to thermally interact with a sensor whose electrical resistance is temperature dependent. Asperities on the data storage medium may be further used as a reference for maintaining a positional relationship between a transducer and the data storage medium. The data storage medium can be implemented as a non-removable or removable disk, a tape, or otherwise. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying Drawings, in which:  
         [0014]      FIGS. 1A, 1B  and IC are diagrammatic illustrations depicting different kinds of asperities that are known to affect conventional magnetic storage devices;  
         [0015]      FIG. 2  is a diagrammatic illustration of an asperity reader in accordance with the present invention that reads an information-encoded pattern of asperities on a data storage medium;  
         [0016]      FIG. 3  is a perspective view of an exemplary construction of the asperity reader of  FIG. 2 ;  
         [0017]      FIG. 3A  is a cross-sectional view taken along line  3 - 3  in  FIG. 3  showing alternative sensor layer geometries affecting thermal diffusivity of the  FIG. 3  asperity reader;  
         [0018]      FIG. 3B  is a cross-sectional view taken along line  3 - 3  in  FIG. 3  showing the use of an optional heat shield and sensor layer configuration affecting thermal diffusivity of the  FIG. 3  asperity reader;  
         [0019]      FIG. 3C  is a cross-sectional view taken along line  3 - 3  in  FIG. 3  showing the use of another optional heat shield and sensor layer configuration affecting thermal diffusivity of the  FIG. 3  asperity reader;  
         [0020]      FIG. 3D  is a cross-sectional view taken along line  3 - 3  in  FIG. 3  showing the use of still another optional heat shield and sensor layer configuration affecting thermal diffusivity of the  FIG. 3  asperity reader;  
         [0021]      FIGS. 4A  and  FIG. 4B  are perspective views of a sensor layer of the asperity reader of  FIG. 3  showing changes in voltage drop across the leads thereof when an asperity is proximate thereto;  
         [0022]      FIGS. 5A, 5B ,  5 C and  5 D are diagrammatic illustrations of alternative constructions of an asperity writer in accordance with the invention that writes an information-encoded pattern of asperities on a data storage medium;  
         [0023]      FIG. 6  is a plan view of a data storage disk medium storing an information-encoded pattern of asperities;  
         [0024]      FIG. 7A  is a plan view of a data storage tape medium storing a linear information-encoded pattern of asperities;  
         [0025]      FIG. 7B  is a plan view of a data storage tape medium storing a helical information-encoded pattern of asperities;  
         [0026]      FIG. 8  is a perspective view of an asperity disk drive constructed in accordance with the present invention;  
         [0027]      FIG. 9A  is a perspective view of an asperity tape drive constructed in accordance with the present invention that employs linear information encoding;  
         [0028]      FIG. 9A  is a perspective view of an asperity tape drive constructed in accordance with the present invention that employs helical information encoding;  
         [0029]      FIG. 10  is a functional block diagram showing an asperity subsystem that may be incorporated in an asperity data storage system of the invention, such as the disk drive of  FIG. 8  or the tape drive of  FIG. 9 ;  
         [0030]      FIG. 11A, 11B  and  11 C are functional block diagrams showing the use of different kinds of asperity transducers in the asperity subsystem of  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0000]     I. Introduction  
         [0031]     The invention will now be described by way of exemplary embodiments shown by the drawing figures (which are not necessarily to scale), in which like reference numerals indicate like elements in all of the several views.  
         [0032]     Turning to  FIGS. 1A, 1B  and  1 C, a discussion of asperities and their effect on magnetic head-media interactions will be briefly set forth to acquaint the reader with physics principals underlying operation of the present invention. In  FIG. 1A , a magnetic disk drive slider  2  carries a read/write head  4  that is assumed to incorporate a magneto-resistive read element and a magneto-inductive write element. As the disk  6  rotates in the direction of the arrow  8 , the slider  2  is carried on an air bearing that causes the head  4  to be positioned at a very small distance from the nominal upper disk surface  10 . This distance is referred to as the flying height of the slider  2  and is shown by reference numeral  12 . The distance  12  can also be referred to as the head-disk air gap.  
         [0033]     It will be seen in  FIG. 1A  that the disk  6  is not perfectly flat or smooth. Rather, as is well known in the disk drive art, the disk  6  will normally have a number of irregularities on its upper surface. One of these is shown as a raised protruberance  14  that extends above the nominal upper disk surface  10 . As the disk  6  rotates beneath the slider  2  and the slider is moved around from track to track during read/write operations, the protruberance  14  will at some point pass under the read/write head  4 . If the protruberance  14  is tall enough, it will cause contact between the disk and the read/write head  4 . This contact may cause frictionally induced heating of the read/write head  4 . Such heating will cause the magneto-resistive read element of the read/write head  4  to experience a proportional increase in resistance local to the point of contact. The effect of this frictionally induced heating and resistance increase is to produce a momentary change in readback signal, which is considered undesirable in conventional magnetic disk drives. In the disk drive art, an imperfection on a magnetic disk surface that causes contact with a read/write head, such as the protruberance  14 , is sometimes referred to as a “contact thermal asperity” or “contact TA.”  FIG. 1B  illustrates the same components as shown in  FIG. 1A , the only difference being that there is a smaller raised protruberance  16  on the disk  6  instead of the larger protruberance  14 . The protruberance  16  is small enough that its does not cause contact between the disk and the read/write head  4 . However, the protruberance  16  produces changes in readback signal strength by changing the thermodynamic equilibrium between the read/write head  4  and the disk  6 . This thermodynamic equilibrium is achieved as a result of heat generated by the magneto-resistive read element of the read/write head  4  during read operations being dissipated (in part) across the air gap  12  to the disk  6  at a relatively constant rate (provided the size of the air gap is relatively constant). The protruberance  16  upsets the thermal equilibrium by reducing the size of the air gap  12  as the protruberance passes under the read/write head  4 . This allows more heat to dissipate from the magneto-resistive read element to the disk  6 , causing a momentary decrease in read element temperature, and a proportional decrease in resistance. The effect of this cooling and resistance decrease is to produce a momentary change in readback signal. In the disk drive art, a raised imperfection on a magnetic disk surface that is not large enough to cause contact with a read/write head  4 , such as the protruberance  16 , is sometimes referred to as a “positive non-contact thermal asperity” or “positive non-contact TA.” The protuberance  16  may also be referred to as a “cooling asperity,” insofar as it produces read element cooling.  
         [0034]      FIG. 1C  illustrates the same components as shown in  FIG. 1A and 1B , the only difference being that there is a depression  18  on the disk  6  instead of a protruberance  14  or  16 . The depression  18  produces changes in readback signal strength in a manner that is analogous to the effect produced by the non-contacting protruberance  16 , except with an opposite result. In particular, the depression  18  upsets the thermal equilibrium between the read/write head  4  and the disk  6  by increasing the size of the air gap  12  as the depression passes under the read/write head  4 . This allows less heat to dissipate from the magneto-resistive read element to the disk  6 , causing a momentary increase in read element temperature, and a proportional increase in resistance. The effect of this heating and resistance increase is to produce a momentary change in readback signal strength. In the disk drive art, a low spot on a magnetic disk surface, such as the depression  18 , is sometimes referred to as a “negative non-contact thermal asperity” or “negative non-contact TA.” The depression  18  may also be referred to as a “heating asperity,” insofar as it produces read element heating.  
         [0035]     Turning now to  FIG. 2 , the present invention contemplates a new form of data storage wherein asperities (positive or negative, contacting or non-contacting), shown by reference numeral  20 , are purposely placed on a storage medium  22  in an encoded pattern in order to influence an asperity reader  24  in close proximity thereto. More particularly, as the storage medium moves in the direction of the arrow  26  (this direction being arbitrary), each asperity  20  will cause an impulsive (e.g., approximately 1 microsecond) temperature change in the asperity reader  24  that produces a proportional change in resistance and a corresponding change in readback signal. The change in readback signal can be processed by a read channel  28  that is adapted to interpret the change as information to produce an output representing information corresponding to the encoded pattern of asperities  20  on the medium  22 . The read channel  28  can be based on the design of a conventional disk drive or tape drive read channel. However, modifications are required so that the thermal asperity readback signal is isolated, amplified and otherwise processed to provide the desired information signal, instead of being filtered out or otherwise eliminated, as is common in conventional read channel circuitry.  
         [0036]     The asperities  20  represent discrete regions on the medium surface that are elevated or depressed relative to the neighboring surface. They can be localized, typically to a few micrometers or less. Ideally, the asperities  20  are durable in the sense that they are not worn down during use. As described in more detail below, the asperities  20  can be formed using several methods, each of which produces asperities having unique characteristics.  
         [0000]     II. Asperity Reader  
         [0037]     The asperity reader  24  can be implemented using a temperature sensitive thin film resistor, the electrical resistance of which increases or decreases during the thermal event. As discussed relative to  FIGS. 1A-1C , a conventional magneto-resistive read head typically has temperature-dependent electrical resistance properties and thus could be used to provide the sensing portion (sensor) of the asperity reader  24 . Exemplary materials that may be used to provide the sensor include tantalum (Ta) and platinum (Pt).  
         [0038]      FIG. 3  illustrates an exemplary design  30  that may be used to construct the asperity reader  24  for use in either a disk drive or a tape drive implementation of the invention. The asperity reader design  30  is based on thin film fabrication techniques of the type commonly used to construct magneto-resistive read elements. A multilayer structure is thus contemplated wherein a hard disk drive-type ceramic substrate material such as Aluminum Oxide-Titanium carbibe (AlTiC) is used to form as a relatively thick ceramic substrate layer  32 . An insulative material such as alumina is deposited onto the ceramic substrate layer  32  to form a relatively thin first insulative layer  34 . A sensor layer  36  (sensor) having a temperature-dependent electrical resistance is formed on the first insulative layer  34 . As indicated above, the sensor  36  can be fabricated using tantalum, platinum or any other material with suitable resistive properties. A relatively thin second insulative layer  38  is formed on the sensor  36 . A thin closure layer  40  made from (for example) hard ceramic similar to the substrate material or the like is formed on or bonded to the insulative layer  38 . The thicknesses of the various layers  32 - 40  of the asperity reader design  30  can be selected according to design requirements and taking into account the relative heat transfer characteristics of the materials chosen. A linear temperature-resistance profile for the asperity reader  24  is acceptable, but is not required insofar as appropriate compensation circuitry can be provided in the read channel  28  to provide a desired readback signal.  
         [0039]     The thermal pulse amplitude for a cooling asperity on the medium  22  is a function of the power dissipation of the sensor  36 , the thermal diffusivity of the sensor plus neighboring films, and the detailed shape of the asperity itself. For example, for a given cooling asperity, the time constant for temperature change (ignoring the temperature rise of the asperity itself) is calculated by the product R * C, where R is the parallel combination of the thermal resistance between the sensor  36  and the remainder of the asperity reader  24  and the characteristic thermal resistance for heat flow from the sensor  36  into the asperity (e.g., in degrees Celsius per watt), and where C is the characteristic heat (thermal) capacity of the sensor  36  (e.g., in Joules per degree Celsius). The characteristic thermal resistance value R is (in part) a function of the thermal resistance of the gap between the sensor and the medium  22 . The characteristic heat capacity value C indicates the ability of the sensor  36  to store heat and represents the amount of energy required to raise the temperature of the sensor by one degree, or conversely, the amount of energy that needs to be transferred out of the sensor  36  to drop its temperature by one degree. The time constant for temperature change (R*C or RC) is the time required for the sensor  36  to reach 63.2% of its maximum temperature differential when undergoing a temperature change event. High diffusivity corresponds to low RC. For the sensor  36 , a high-thermal diffusivity value (low RC) thus means there will be a rapid large temperature drop in the brief time period that the sensor is influenced by an asperity, which translates to large pulse amplitude.  
         [0040]     The response of the sensor design  30  to cooling asperities can therefore be adjusted by altering its thermal diffusivity. Apart from sensor material selection, the thermal diffusivity of the sensor  36  is largely dictated by its geometry. For example, as shown in  FIG. 3A , one way to increase thermal diffusivity is to reduce sensor thermal resistance, for example by increasing the cross-sectional area for heat flow from the sensor to the medium. As shown in  FIG. 3B , another way that thermal resistance can be reduced is to provide a heat sink shield  46  in close proximity to the sensor  36 . The shield  46  can be a thin film-deposited metal, such as one of the alloys of iron, nickel or cobalt commonly used in magnetic head fabrication, except that the shield does not posses magnetic properties. The sensor  36  transfers heat to the shield  46 , and the shield  46  dissipates heat into the medium  22 , thereby increasing the thermal diffusivity of the sensor  36 , depending on its design. Generally speaking, shield volume and specific heat must be considered when designing for low heat capacity C, for lowering the sensor&#39;s RC value. Although not shown in  FIG. 3B , a second shield  46  could be placed on the opposite side of the sensor  36 , thereby further reducing thermal resistance (like fins on a conventional transistor heat sink).  FIG. 3C  shows another construction that illustrates the sensor  36  at a location which is recessed from the air bearing surface. In comparison to  FIG. 3B , this minimizes the cross-sectional area of the sensor-shield structure at the air bearing surface, thereby allowing higher areal asperity densities on the medium  22 .  FIG. 3D  also shows another recessed sensor construction with shields  46  on both sides of the sensor  36 .  
         [0041]     Returning now to  FIG. 3 , and as further illustrated in  FIGS. 4A and 4B , the side portions of the sensor  36  can be extended perpendicularly away from the plane of the medium  22  to provide leads  42  for attachment to a sense current source, such as the read channel  28  (see  FIG. 2 ). When the sense current is applied, a voltage drop will develop across the leads  42  according to the net electrical resistance of the sensor  36 . As indicated above, the electrical resistance of the material of the sensor  36  will vary depending on its temperature.  FIG. 4A  illustrates a first state of the sensor layer  36  wherein there is no asperity proximate thereto on the medium  22 . A hypothetical voltmeter  44  placed across the leads  42  indicates a first voltage level.  FIG. 4B  illustrates a second state of the sensor layer  36  wherein there is an asperity  20  proximate thereto moving at the velocity of the medium  22 . The hypothetical voltmeter  44  placed across the leads  42  now shows a second voltage level that is different than the first. In particular, if the sensor  36  has a positive temperature coefficient, and if the asperity  20  is a contact thermal asperity as shown in  FIG. 1A , or a negative non-contact thermal asperity as shown in  FIG. 1C , the second voltage level will be higher than the first voltage level due to an asperity-induced temperature/resistance increase in the sensor  36 . If the asperity  20  is a positive non-contact thermal asperity as shown in  FIG. 1B  (and the sensor layer  36  has a positive temperature coefficient), the second voltage level will be lower than the second voltage level due to an asperity-induced temperature/resistance decrease in the sensor  36 . After the asperity  20  moves past the sensor  36 , the effects of the asperity will be quickly removed, the resistance of the sensor will return to its original level, and first voltage level will resume. As persons skilled in the art will appreciate, the read channel  28  can be designed so that the momentary change in voltage level caused by the asperity  20  is interpreted as information, such as a digital “ 1 ” or “ 0 .”  
         [0042]     It should be further understood that the signal response characteristics of the sensor  36  can be controlled by asperity geometry and operating characteristics. Relative to asperity geometry, the height of the asperities  20  will influence readback signal-to-noise ratio. For non-contact asperity configurations, the temperature/resistance change in the sensor  36  will be greatest when positive asperities are tall and negative asperities are deep. Thus, asperity height is a candidate for increasing storage density. For contact asperity configurations, the higher the relative speed between the medium  22  and the sensor  36 , the larger the signal. This means that data access burst speeds can be increased without sacrificing performance, and perhaps even increasing performance.  
         [0000]     III. Asperity Writer  
         [0043]     Turning now to  FIGS. 5A-5D , there are a number of ways that the asperities  20  can be formed on the medium  22  in accordance with the invention. In  FIG. 5A , the asperities  20  are formed using a texturing writer  50 A constructed, for example, as a laser writer that directs a laser beam  52  onto the medium  22 . The asperities  20  may thus be created by way of laser texturing. This process is best suited for producing negative non-contact asperity configurations (heating asperities), but could also be used to produce contact and positive non-contact asperities (cooling asperities), by removing material on each side of an asperity to be defined. In  FIG. 5B , the asperities  20  are formed using an impact writer  50 B constructed as an imprinting writer that impresses a stylus  54  into the medium  22 . The asperities  20  may thus be created by way of indenting. This process is again best suited for producing negative non-contact asperity configurations (heating asperities), but could also be used to produce contact and positive non-contact asperities (cooling asperities). In  FIG. 5C , the asperities  20  are formed using a toner writer  50 C constructed as a laser print head that applies toner  56  onto the medium  22  after it has been scanned with a pattern-defining laser. The asperities  20  may thus be created by way of laser toner printing. This process is best suited for producing contact or positive non-contact asperity configurations (cooling asperities), but could also be used to produce negative non-contact asperities (heating asperities) by depositing material on each side of an asperity to be defined. In  FIG. 5D , the asperities  20  are formed using an ink jet writer  50 D constructed as an ink jet print head that applies ink  58  onto the medium  22 . The asperities  20  may thus be created by way of ink jet printing. This process is again best suited for producing contact or positive non-contact asperity configurations (cooling asperities), but could also be used to produce negative non-contact asperities (heating asperities). It will be appreciated that other techniques for forming the asperities  20  may also be used in accordance with the invention.  
         [0044]     For any of the foregoing asperity writing techniques, nanotechnology principles may be brought to bear on the asperity formation process. Thus, the laser writer of  FIG. 5A , the impact writer of  FIG. 5B , the toner writer of  FIG. 5C  and the inkjet writer of  FIG. 5D , may all be constructed using nanofabrication techniques in order to create high density nanoscale asperities. The present invention thus contemplates high density asperities being formed using techniques such as nano-imprinting, nano-indenting, nano-particle deposition, etc. For example, arrays of carbon-60 spheres (so-called “Bucky Balls”) may be used for encoding data.  
         [0000]     IV. Asperity Data Storage Systems  
         [0045]     The principles of the present invention can be embodied in either a disk drive storage system or a tape drive storage system, or perhaps some other data storage system not based on disk or tape media, such as systems in which a storage medium is fixed and a transducing apparatus having one or more transducers moves relative to the medium (e.g., as per the arrangement used in highly parallel very dense AFM data storage systems).  FIG. 6  represents an enlarged plan view of a rigid (or flexible) disk medium  60  wherein the asperities  20  shown in  FIG. 2  are recorded in concentric tracks  62  in a manner analogous to the recording of data on magnetic, optical and magneto-optical disks. Asperities that represent user data can be formed in data sectors  64 . Servo sectors  66  may also be provided in which asperities representing information analogous to magnetic disk servo fields are formed for positioning an asperity reader and/or writer relative to the disk medium  60 .  FIG. 7A  represents an enlarged plan view of a flexible tape medium  70 A wherein the asperities  20  shown in  FIG. 2  are recorded in linear tracks  72 A in a manner analogous to the linear recording of data on magnetic tape. Asperities that represent user data can be formed in data sectors  74 A. Servo sectors  76 A may also be provided in which asperities representing information analogous to magnetic tape servo fields are formed for positioning an asperity reader and/or writer relative to the tape medium  70 A.  FIG. 7B  represents an enlarged plan view of a flexible tape medium  70 B wherein the asperities  20  shown in  FIG. 2  are recorded in helical tracks  72 B in a manner analogous to the helical recording of data on magnetic tape. Asperities that represent user data can be formed in data sectors  74 B. Servo sectors  76 B may also be provided in which asperities representing information analogous to magnetic tape servo fields are formed for positioning an asperity reader and/or writer relative to the tape medium  70 B. The media  60 ,  70 A and  70 B may be either uncoated or coated using conventional materials.  
         [0046]     A. Asperity Disk Drive  
         [0047]     Turning now to  FIG. 8 , an exemplary asperity disk drive  80  is shown that may be constructed in accordance with the principles of the present invention. The disk drive  80  includes a base casting  82  that supports drive components (not shown) for spinning a disk  84  at high rotational speed. The disk  84  can be either fixedly mounted in the disk drive  80 , or it could be removable. If the disk  84  is fixed, other disks (not shown) may also be carried by the drive components to form a spaced vertically stacked disk platter arrangement. The disk  84  is formed from a suitable disk substrate that is capable of being configured with a pattern of asperities, as shown in  FIG. 6 . For example, disk  84  could be made from the same material used to manufacture magnetic, optical or magneto-optical disks.  
         [0048]     Data access to the disk  84  is achieved with the aid of an actuator/suspension  86  that is mounted for rotation relative to the base casting  82 . The free end of the actuator/suspension  84  mounts a transducer-carrying slider  86  that mounts an asperity transducer (not shown in  FIG. 8 ) constructed in accordance with the present invention. As described in more detail below in connection with  FIG. 10 , this asperity transducer can be implemented using the asperity reader  24  of  FIG. 2 , or any of the asperity writers  50 A- 50 D of  FIGS. 5A-5D , or as a merged head that combines an asperity reader and an asperity writer so as to be capable of performing asperity read/write operations. As is conventional, the actuator/suspension  86  moves the slider  88  generally radially across the surface of the disk  84  so that the transducer is able to trace concentric data tracks on the disk. As further described in more detail below relative to  FIG. 10 , the asperity disk drive  80  further includes onboard electronics that allow it to communicate with a host, such as a general purpose computer or other information processing system.  
         [0049]     B. Asperity Tape Drive  
         [0050]     Turning now to  FIG. 9A , an exemplary asperity tape drive  90  is shown that may be constructed in accordance with the principles of the present invention. The asperity tape drive  90  includes a slot  92  for receiving a tape cartridge  94  into engagement with an internal tape interface system (not shown). The tape cartridge  94  carries a tape medium  96  within a housing  98 . The tape medium  96  is formed from a suitable tape substrate that is capable of being configured with a linear pattern of asperities, as shown in  FIG. 7A . For example, tape medium  96  could be made from the same material used to manufacture magnetic recording tape.  
         [0051]     The tape medium is carried on a supply reel  100  and feeds a take up reel  102  around an optional capstan tape guide roller  104 . Although not shown, the internal tape interface system within the tape drive  90  conventionally includes a pair of drive motors that are adapted to engage and drive the supply reel  100  and the take-up reel  102  when the cartridge  94  is inserted in the slot  92 . In addition, an asperity transducer (not shown in  FIG. 9A ) will be operatively positioned relative to the tape medium  96  when the cartridge  94  is so engaged. As described in more detail below in connection with  FIG. 10 , this asperity transducer can be implemented using the asperity reader  24  of  FIG. 2 , or any of the asperity writers  50 A- 50 D of  FIGS. 5A-5D , or as a merged head that combines an asperity reader and an asperity writer so as to be capable of performing asperity read/write operations. As further described in more detail below relative to  FIG. 10 , the asperity tape drive  90  additionally includes onboard electronics that allow it to communicate with a host, such as a general purpose computer or other information processing system.  
         [0052]      FIG. 9B  illustrates an alternative asperity tape drive  105  that employs a helical encoding scheme in which a tape medium  106  streams around guide rollers  107  and across the surface of an obliquely angled rotating drum  108 . An asperity transducer  109  is operatively mounted on the drum  108  to scan the tape medium  106  in helical fashion (as per  FIG. 7B ). As described in more detail below in connection with  FIG. 10 , the asperity transducer  109  can be implemented using the asperity reader  24  of  FIG. 2 , or any of the asperity writers  50 A- 50 D of  FIGS. 5A-5D , or as a merged head that combines an asperity reader and an asperity writer so as to be capable of performing asperity read/write operations. As further described in more detail below relative to  FIG. 10 , the asperity tape drive  105  additionally includes onboard electronics that allow it to communicate with a host, such as a general purpose computer or other information processing system.  
         [0053]     C. Asperity Drive Subsystem  
         [0054]     Turning now to  FIG. 10 , a functional block diagram illustrates an exemplary asperity drive subsystem  110  that may be used to implement either the asperity disk drive  80  of  FIG. 8 , the asperity tape drive  90  of  FIG. 9A , or the asperity tape drive  105  of  FIG. 9B . The asperity drive subsystem  110  includes plural components providing control and data transfer functions for reading and/or writing host data on an asperity disk or tape medium in one or more tracks for the benefit of a host  112 . By way of example only, such components may include a channel adapter  114 , a microprocessor controller  116 , a data buffer  118 , a read/write data flow circuit  120 , a motion control/servo control system  122 , and a media interface system  124  that includes a motor driver unit  125  and an asperity transducer  126 .  
         [0055]     The microprocessor controller  116  provides overhead control functionality for the operations of all other components of the asperity subsystem  110 . As is conventional, the functions performed by the microprocessor controller  116  can be programmed via microcode routines (not shown) according to desired storage system operational characteristics. During data write operations (with all dataflow being reversed for data read operations), the microprocessor controller  116  activates the channel adapter  114  to perform the required host interface protocol for receiving an information data block. The channel adapter  114  communicates the data block to the data buffer  118  that stores the data for subsequent read/write processing. The data buffer  118  in turn communicates the data block received from the channel adapter  114  to the read/write dataflow circuitry  120 , which formats the device data into physically formatted data that may be recorded on an asperity storage medium. The read/write dataflow circuitry  120  is responsible for executing all read/write data transfer operations under the control of the microprocessor controller  116 . Formatted physical data from the read/write circuitry  120  is communicated to the media interface system  124 .  
         [0056]     As stated, the media interface system  124  includes a motor driver unit  125  and an asperity transducer  126 . The motor driver unit  125  contains components for controlling the movement between an asperity medium  128 , be it a disk, tape or fixed medium, and an asperity transducer  126  in operational proximity thereto. For example, if the asperity drive subsystem  110  is implemented in the disk drive  80  of  FIG. 8 , the drive components of the media interface system  124  will be controlled by the motion control system  122  and the motor driver circuit  125  to execute such actions as spinning the disk medium  84  up and down, and manipulating the transducer/suspension  86  to position the transducer-carrying slider  88  during such track positioning operations as seek, settle and track following. Note that conventional servo-control techniques can be used with servo sectors recorded as asperity servo information. By way of further example, if the asperity drive subsystem  110  is implemented in the linear tape drive  90  of  FIG. 9A , the drive components of the media interface system  124  will be controlled by the motion control system  122  and the motor driver circuit  125  to execute such actions as forward and reverse recording and playback, rewind and other tape motion functions. In addition, in a multi-track tape drive system, the motion control system  122  will transversely position the tape drive&#39;s asperity transducer(s) relative to the direction of longitudinal tape movement in order to read or write data in a plurality of tracks. Note that head servo-control can be accomplished using tape edges and/or tracks with prewritten asperity servo information. Compensating for tape width changes can be accomplished via in situ calibration prior to reading.  
         [0057]     The asperity transducer  126  can be implemented as part of the transducer carrying slider  88  in the asperity disk drive  80  of  FIG. 8 , or as a tape head transducer in the asperity tape drive  90  of  FIG. 9A  or the tape drive  105  of  FIG. 9B . In each environment, the asperity transducer unit  126  can embody (1) an asperity reader  130  of the type shown and described in connection with  FIGS. 3, 4A  and  4 B, or (2) an asperity writer  140  of the type shown in  FIGS. 5A-5B , or (3) both. In the first configuration, which is shown in  FIG. 11A , a read-only capability would be provided in a manner analogous to a conventional CDROM drive. In the second configuration, which is shown in  FIG. 11B , a write-only capability would be provided in a manner that is analogous to conventional devices used to produce prerecorded storage media. In the third configuration, which is shown  FIG. 11C , a read-write capability would be provided in a manner analogous to a conventional magnetic disk or tape drive or an optical or magneto-optical disk drive with write-once-read-many data recording capability.  
         [0000]     V. Conclusion  
         [0058]     Accordingly, an asperity data storage system, method and medium have been disclosed. Applications for the inventive subject matter include, but are not limited to, those requiring immunity from the degrading effects that magnetic fields can have on conventional magnetic storage media, applications involving high readback speeds (which actually increase asperity detection), and applications involving Write-Once-Read-Many (WORM) media that require long shelf life. The achievable asperity areal densities that can be read back by an asperity reader as described above are expected to be on the order of 1×10 6  to 1×10 7  asperities per square inch, or better. The limit is set by the asperity characteristics and by the thermal response of the asperity reader. When the asperities are closer together than several micrometers, the cooling pulses will begin to overlap, making decoding more difficult. In general, it is advantageous to have the sensor dimensions smaller than those of the asperities for ease of decoding. Because the asperities are written along discrete tracks, the track pitch needs to be large enough to prevent two sensors from detecting the same asperity. Track pitch and linear densities are on the order of 10 micrometers.  
         [0059]     While various embodiments of the invention have been shown and described, it should be apparent that many variations and alternative embodiments could be implemented in accordance with the teachings herein. For example, in addition to using an asperity reader as disclosed herein for reading asperity patterns representing stored information, such a reader could be used for characterizing asperity distributions on magnetic recording media, where asperities are generally undesirable. The disclosed asperity reader could be used, for example, in a tape transport system that runs the tape media at relatively high speed, such as 10-20 meters/second. This high speed makes some asperities more easily detected and counted. This could help a manufacturer understand and monitor media surface quality.  
         [0060]     It is understood, therefore, that the invention is not to be in any way limited except in accordance with the spirit of the appended claims and their equivalents.