Patent Publication Number: US-2009231978-A1

Title: Long-term digital data storage

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/765,937 entitled “LONG-TERM DIGITAL DATA STORAGE”, which was filed on Jun. 20, 2007 for Barry M. Lunt et al. 
    
    
     BACKGROUND 
     Computers have steadily increased in popularity since their introduction into modern society. Computers and other types of digital electronics have simplified many tasks and facilitated new innovations that have changed the way we live. Today, with personal digital assistants (PDA&#39;s), cellular telephones, digital cameras, digital video recorders, digital music players and widespread Internet connectivity, people are recording more data than ever before to a wide variety of digital media storage devices. For example, many people have collections of digital photos, videos, songs, web pages, text files and other digital content stored on hard drives, CD&#39;s, DVD&#39;s, flash drives and other types of digital storage media. 
     Digital data storage media has many advantages. For example, all types of digital storage media allow for perfect reproduction and storage of digital files. Such files can be easily transferred to and from various digital storage media without any loss of data or quality. Another notable advantage of digital recordable media lies in its consumer appeal. From flash drives to hard drives to multi-layer DVD&#39;s, nearly all types of digital storage media have grown in capacity and substantially decreased in price. As a result, digital storage devices continue to gain popularity with consumers. 
     Optical storage devices have particularly grown in consumer use, in large part due to the ease of use and ubiquity of optical media players and recorders. Optical storage media can be categorized into two general types: commercially manufactured media in which the data layer is “stamped” using a laser-cut mold, and consumer-writable media in which the data layer is “burned” using a CD or DVD burner. Such consumer-writable media (e.g. CD-R/RW&#39;s, DVD±R/RW/RAM, etc.) is often used as long term data storage for photos, songs and other files. 
     Although such burnable optical media are widely considered to keep data forever, this is not the case. Such burnable optical media tends to degrade over time. For instance, in a typical write operation to an optical media, an energy source is focused on the media in a pattern of intense bursts, thus creating marks that can be interpreted as 1&#39;s and 0&#39;s. This “burning” process chemically alters the molecules of the optical media data layer, which is usually made of some type of metal alloy and an optical dye. Though the term “burning” implies some high level of permanence, the chemical alteration is, in fact, not permanent and actually degrades each time the media is read. Storing at high temperatures, high humidity, or high light levels can also degrade the media. Over time, the optical contrast between the marks representing 1&#39;s and 0&#39;s fades and the data becomes unreadable despite the confidence that consumers and even sophisticated technicians place in such media. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention are directed to recording digital data on an optically ablatable digital storage media. In one embodiment, a device configured to ablate portions of ablatable material on an optically ablatable digital storage media receives digital data that is to be recorded on a recording layer of an optically ablatable digital storage media. The recording layer is formed on a substrate with zero or more intervening layers between the recording layer and the substrate. The recording layer includes ablatable material capable of storing digital data. The device ablates the ablatable material in the recording layer according to a sequence defined by the received digital data such that the ablated portions correspond to data points of the received digital data. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To further clarify the above and other advantages and features of embodiments of the present invention, a more particular description of embodiments of the present invention will be rendered by reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  illustrates a component architecture in which embodiments of the present invention may operate by, for example, recording digital data on an optically ablatable digital storage media; 
         FIG. 2  illustrates a flowchart of an example method for recording digital data on an optically ablatable digital storage media; 
         FIG. 3A through 3D  each illustrate an example cross-section of various embodiments of ablatable media items; 
         FIG. 4A through 4C  each illustrate an example cross-section of various alternative embodiments of ablatable media items; 
         FIG. 5  illustrates a component environment in which digital data may be recorded on an optically ablatable digital storage media; 
         FIG. 6  illustrates an alternative component environment in which digital data may be recorded on an optically ablatable digital storage media; and 
         FIG. 7  illustrates an example cross-section of an alternative embodiment of an ablatable media item. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments described herein are directed to recording digital data on an optically ablatable digital storage media. In one embodiment, a device configured to ablate portions of ablatable material on an optically ablatable digital storage media receives digital data that is to be recorded on a recording layer of an optically ablatable digital storage media. The recording layer is formed on a substrate with zero or more intervening layers between the recording layer and the substrate. The recording layer includes ablatable material capable of storing digital data. The device ablates the ablatable material in the recording layer according to a sequence defined by the received digital data such that the ablated portions correspond to data points of the received digital data. 
       FIG. 1  illustrates a component architecture  100  in which the principles of the present invention may be employed. Component architecture  100  includes ablation device  101 . In some embodiments, ablation device  101  may be configured to ablate portions of ablatable material on an optically ablatable digital storage media. Ablation is a process of instantaneously applying a sufficient amount of energy to an object that the object&#39;s ablatable material is removed. In some cases, the ablated material is evaporated into a gas. Examples of using ablation to record digital data will be explained in greater detail below. The evaporative changes made to the ablatable material are more permanent in nature and are not likely to rapidly degrade over time. It should be noted that the term “instantaneously” is used to imply that the process is performed quickly, but should not be limited to any certain amount of time. Furthermore, the term “permanent,” as used herein, implies exceptional robustness, durability and a lack of any tendency to degrade, and is not intended to imply infinite permanence. 
     The amount of energy required to instantaneously raise the temperature of an ablatable material will vary greatly depending on the material. For example, glassy carbon is a carbon structure with multiple, tightly bound carbon-carbon double bonds which give glassy carbon absorptive properties advantageous for ablation. Other materials will similarly be more or less suited to ablation. Another measure used in the process of ablation is the amount of energy used to exact the change. This measurement will be referred to herein as an ablation energy. It should be noted that complete ablation is not always necessary. In some cases, partial ablation of the ablatable material may be sufficient. In other words, ablation may be considered complete even though some ablatable material remains at the point of ablation. The same is true of the reflective layer, as will be explained below. In some cases, the reflective layer need only reflect a portion of the ablation energy to be successful. 
     In some embodiments, the ablation energy may be measured as a unit of energy per unit volume of material. For example, thicker layers of ablatable material may require a greater amount of energy to ablate. Other materials may also be more or less likely to ablate, depending on the type of material and other conditions. Many factors affect both the desired temperature and the desired energy level. Other factors may also be varied to aid in ablation such as exposure time or wavelength of the energy source. For example, different wavelengths may be used to match the properties of the ablative layer such that ablation occurs more readily. 
     In some cases, a thicker layer of material may necessitate a longer or more intense exposure to ablation energy. Still other factors may include ambient temperature, humidity, the process by which the ablatable material was formed, the process by which the ablatable material was bonded to other materials in the ablatable media item, the type of ablation energy used in the process and the type and thickness of the reflective layer (when present). In some cases, measurements for exposure times, ablation energies and optimal thicknesses for any given ablatable layer and/or reflective layer are based on the type of material, thermal conductivity of the material, the surrounding environment and the amount of energy being imparted. 
     One of the deciding factors that determines whether ablation can occur or not is the total energy absorbed per unit surface area/volume of material that is being ablated. In some embodiments, it may be possible to use a conventional CD or DVD writer by adjusting exposure time and/or increasing the laser energy. The imparted energy should be sufficient to ablate the material in a particular portion of the media. The ablation process produces a permanent change in the ablated material and is highly robust against the many forms of degradation. 
     Referring again to  FIG. 1 , in some embodiments, the energy used for ablation may be provided by energy source  115 . Energy source  115  may provide various types of energy including thermal, electrical, magnetic, radiant (light or optical energy) and/or sound energy. Energy source  115  may be configured to write to and read from ablatable media  105  via read/write channel  110 . Read/write channel  110  may be any type of communication link including both physical and wireless links. Ablatable media  105  may be any type of digital media capable of being ablated. In some embodiments, ablatable media  105  may include optical discs similar to conventional CDs and DVDs. 
       FIG. 1  also includes an ablatable media availability determination module  125 . Ablatable media availability determination module  125  may be configured to detect when ablatable media  105  is available for communication via read/write channel  110 . In other embodiments, an ablation device user (not shown) may determine that ablatable media  105  is available for communication via read/write channel  110 . Additionally or alternatively, ablatable media availability determination module  125  may be configured to communicate with ablation module  120 . 
     Ablation module  120  may be configured to receive digital data  130  from digital data receiving module  135 . In some embodiments, digital data receiving module may be configured to receive digital data  130  which is communicated to ablation module  120 . Digital data  130  may represent any type of information in any format. Furthermore, the data may be encrypted, compressed, or otherwise modified from its original form. Digital data  130  may be received in organized portions such as files, or may be received as a stream of data. Digital data receiving module  135  may be configured to receive and, in some cases, process digital data  130  in some manner. Such processing may include encryption or decryption, compression or decompression, modifying, storing or any other form of data processing. The components of  FIG. 1  will be described in greater detail below with reference to  FIGS. 2-5 . 
       FIG. 2  illustrates a flowchart of a method  200  for recording digital data on an optically ablatable digital storage media. The method  200  will now be described with frequent reference to the components and data of environment  100 , ablatable media embodiments illustrated in  FIGS. 3A-3D ,  4 A- 4 C and  FIG. 7 , and the ablation environments  500  and  600  of  FIGS. 5 and 6 , respectively. As used herein, reference to  FIGS. 3-4  implies reference to  FIGS. 3A-3D  and  4 A- 4 C. In some embodiments, method  200  may be carried out by a computer system. The computer system may comprise a special purpose or general-purpose computer including various types of computer hardware, as discussed in greater detail below. 
     Embodiments within the scope of the present invention include computer-readable media for carrying or having computer-executable instructions or data structures stored thereon. Such computer-readable media can be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise physical (or recordable type) computer-readable media including RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code means in the form of computer-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer. Additionally, when information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a computer, the computer properly views the connection as a computer-readable medium. Thus, any such connection is also properly termed a computer-readable medium. Combinations of the above should also be included within the scope of computer-readable media. 
     Computer-executable instructions comprise, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. 
     Returning to  FIG. 2 , in some embodiments, method  200  includes an act of determining that an optically ablatable digital storage media is available for recording (act  210 ). For example, ablatable media availability determination module  125  may be configured to determine that optically ablatable digital storage media  105  is available for recording. In some cases, ablatable media availability determination module  125  may only be configured to determine that a media item is present and available for ablation. In other cases, ablatable media availability determination module  125  may be configured to determine that a media item is present and that the media item is ablatable. 
     Optically ablatable digital storage media  105 , as shown by way of example in  FIG. 3A , may include an ablatable data layer  310 A formed on structural support layer  320 A with no intervening layers between ablatable data layer  310 A and structural support layer  320 A, as shown in  FIG. 3A . 
     In some embodiments, ablatable data layer  310 A is a recording layer capable of storing information represented by ablated data points  315 A. Ablated data points  315 A are portions of ablatable data layer  310 A that have been ablated. That is, ablatable material that once filled ablated data points  315 A has been ablated, or evaporated into a gas. Ablated data points  315 A may appear in any order, in any width, or may not occur at all for any given area of ablatable data layer  310 A. For example, if digital data is being “written” or ablated (these terms may be used interchangeably herein) into ablatable data layer  310 A, the data may correspond to variable length portions of 1&#39;s and 0&#39;s. Thus, according to the sequence of 1&#39;s and 0&#39;s as defined by the digital data, more or fewer ablated data points  315 A may exist in any given portion of ablatable data layer  310 A. Furthermore, ablated data points  315 A may take a variety of form and shapes. For example, ablated data points  315 A may be circular, oval, square, rectangular, irregularly-shaped, or any variation thereof that is capable of providing a sufficient optical contrast. 
     For instance, as illustrated in  FIG. 5 , environment  500  includes a depiction of an ablation device  501  ablating ablatable data layer  520 . As ablatable media  505  spins in spinning direction  530 , laser diode  502  ablates ablatable data layer  520  in a pattern corresponding to digital data  130 . Once a portion of ablatable data layer  520  has been ablated, resulting ablated data points  515  remain in the data layer.  FIG. 5  depicts one method of ablation where laser diode  502  shines a pulse of light or laser beam  510  onto ablatable data layer  520 . The portion of ablatable data layer  520  directly below laser diode  502  is shown to be ablated, as if laser diode  502  had just finished ablating that data point. 
     It should be noted that the portion of ablatable media  505  shown in  FIG. 5  is merely a cross section and only shows one sequence of ablated data. In some embodiments, digital data may be stored in ablatable data layer  520  as a series of tracks, similar to tracks in a CD or DVD. These tracks may begin from the center of the media and continuously work outwardly in a spiral fashion. Or, alternatively, the tracks may begin on the outside and work inwardly. Other embodiments may include ablating the media in alternative, non-spiral patterns in random or pseudo-random locations on the ablatable media item. Furthermore, ablatable media  105  may be stationary in some embodiments, while ablation device  501  with energy source  502  moves to various portions of the media item to ablate the item at those portions. In any of these embodiments, media item  105  may be in the shape of a disc, a square, a cube or any other shape compatible with the ablation device. 
     Although environment  500  depicts ablation device  501  and laser diode  502  positioned above ablatable media  505 , it is also possible, as shown in environment  600  of  FIG. 6 , for ablation device  601  and laser diode  602  to be positioned below ablatable media  605 . Similar to  FIG. 5 ,  FIG. 6  shows ablatable data layer  620  of ablatable media  605  being ablated by ablation device  601  using laser diode  602 . Ablatable media  605  is spun in the direction indicated by arrow  630  and ablatable data points  615  are similarly created corresponding to a pattern indicated by digital data  130 . 
     In some embodiments, ablation devices  501  and  601  correspond to ablation device  101  of  FIG. 1 . It should also be noted that any type of ablatable media  105  may be ablated in the manners shown in  FIGS. 5 and 6 , respectively. For example, laser beam  510 / 610  may be modified to shine through one or more layers before ablating ablatable material in data layer  520 / 620 . For example, as shown in  FIG. 6 , laser beam  610  may be shone through structural support layer  625  before ablating material on data layer  620 . Furthermore, it should be noted that environments  500  and  600  may function in any type of geometric variation, other than as shown in  FIGS. 5 and 6 , such as sideways, upside down or any other position. 
     Again referring to  FIG. 1 , ablation device  101  and/or energy source  115  may be moveable in relation to the ablatable media. In some embodiments, ablation device  101  and/or energy source  115  may be attached to a servo motor (not shown) or other means of moving the device  101  and/or energy source  115  in relation to the media  105 . 
     Ablatable media availability determination module  125  (“module  125 ”) may be configured to determine the availability of ablatable media  105  in a variety of manners. For example, module  125  may be configured to communicate with energy source  115  which is capable of reading from or writing to ablatable media  105  via read/write channel  110 . In some embodiments, module  125  may be configured to perform automatic checks to determine whether an ablatable media item is available for reading or writing. In other embodiments, module  125  may refrain from determining availability of any ablatable media until receiving an indication from a computer user or software module that one or more ablatable media items are ready to be accessed. Additionally or alternatively, ablatable media availability determination module  125  may be configured to communicate with ablation module  120 . In such embodiments, module  125  may indicate to ablation module  120  that one or more ablatable media items  105  is available for reading from and/or writing to. 
     In some embodiments, at least one of the zero of more intervening layers includes one or more intervening layers and at least one of the one or more intervening layers is a reflective layer. For example,  FIG. 3C  depicts reflective layer  340 C as an intervening layer between ablatable protective-absorptive layer  330 C and structural support layer  320 C. Reflective layer  340 C may comprise a single material or a combination of materials. For example, reflective layer  340 C may comprise titanium or chromium. In some embodiments, the titanium or chromium would be vapor deposited or sputtered onto the polycarbonate substrate. It may be advantageous, in some cases, to perform a plasma cleaning of the polycarbonate substrate to oxidize the structural support layer surface to which the reflective layer will be bonded. Titanium and chromium traditionally stick well to such oxidized surfaces. 
     A reflective layer may be applied to any of ablatable media  301 A-D, but is only shown in  FIGS. 3C and 3D . Not only the reflective layer, but also any layer used in ablatable media  301  may be applied or “bonded” using some type of thin film deposition. Thin film deposition encompasses multiple methods of applying material to an object including sputtering, electron beam evaporation, plasma polymerization, chemical vapor deposition, spin-coating, dip-coating, evaporative deposition, electron beam physical vapor deposition, sputter deposition, pulsed laser deposition, ion beam assisted deposition, electroplating, molecular beam epitaxy or any other thin-film or thick-film deposition technique. In some cases, each layer may be applied subsequently, or in other cases, previously bonded layers may be applied to other (previously-bonded) layers. 
     For example, in  FIG. 3D , ablatable protective-absorptive layer  330 D and reflective layer  340 D may be bonded while adhesion layer  350  and structural support layer are bonded. Each combination of layers,  330 D/ 340 D and  350 / 320 D, respectively, may then be bonded to each other. An adhesion layer (e.g. adhesion layer  350 ) may be used to adhere any one layer to any other layer. Adhesive materials used in adhesion layer  350  may include any type of natural or synthetic materials, including metals, alloys, polymers, copolymers, ceramics, or organic small-molecules, or adhesives including any type of drying, contact, hot melt, light curing, reactive, pressure sensitive or other adhesives. Other layer combinations, layer orderings and/or layer bonding types are also possible. In some cases, it may be possible to use existing CD or DVD manufacturing techniques and/or manufacturing machines. 
     It should be noted in  FIGS. 3 ,  4  and  7  that the layers depicted in ablatable media  301 / 401 / 701  are not drawn to scale and each layer may be much larger or smaller in size in relation to the other layers. For example, structural support layer  320 A may be much thicker than other layers in order to provide structural rigidity and robustness. In some cases, it may be advantageous for structural support layer  320 A to have high surface uniformity. That is, it may be optimal for structural support layer&#39;s surfaces to be as smooth and flat as possible. Structural support layer  320 A may be formed using polycarbonate, silica, aluminum, silicon wafers, glass or glass-type material, or any other material that has high surface uniformity. Ablatable data layer  310 A may also have an optimal thickness between 1-500 nanometers thick. Thickness of other layers such as reflective layer  340 C, adhesion layer  350 , protective layer  425 A, absorptive layer  470  and ablatable protective-absorptive layer  330 D may similarly be between 1-500 nanometers. In alternative embodiments, thicknesses of the various layers could be more or less than the 1-300 nm range mentioned above. Furthermore, although the surfaces of the various layers shown in  FIGS. 3 ,  4  and  7  are depicted as being flat, the surfaces may be curved, beveled, tapered or indented. Additionally or alternatively, the surfaces may have pits, dips or other markings. For example, one or more of the surfaces may have tracking information embedded in the surface. 
     As mentioned above, layers may be formed and/or applied in a variety of ways. Examples other than those mentioned above include the following: a layer may be spin-coated onto a substrate and then caused to polymerize (cure) using UV light, a layer may be organically grown using various biological agents, characteristics of a layer may be altered at a certain depth, thereby effectively forming a layer, or magnetic nanoparticles may be applied to one or more of the layers such that a magnetic field could draw them to one side, thereby generating a sufficient gradient that, in effect, forms a layer. Other methods for creating and/or applying layers to an ablatable media may also be used. 
     In some cases, when sufficient optical contrast exists between the data layer and any subsequent layer, a reflective layer may or may not be included as a part of ablatable media  301  (as shown in  FIGS. 3A and 3C ). For example, if sufficient optical contrast exists between ablatable data layer  310 A and structural support layer  320 , a reflective layer may not be necessary for data to be read from and written to the media item. In some cases, a reflective layer provides proper optical contrast between layers such that data can be read from the media. For example, when a laser used to read digital data hits the data portion of the media item, the energy will be absorbed and little to no energy will be reflected. However, when the laser hits the reflective layer, the energy will be reflected and read as a reflection (corresponding to a digital 1 or 0). In other cases, an appropriate optical contrast may be provided without a reflective layer using various types of chemicals or other materials to generate a gradient effect that enhances the optical contrast. 
     In some embodiments, a reflective layer may be used to ensure that the ablation energy does not get transferred to any layers beyond the reflective layer. In such cases, the energy beam would ablate the material in the ablatable data layer and, once the beam reached the reflective layer, the beam would be reflected and thus not travel beyond the reflective layer. Detecting that an energy beam has reached a reflective layer and reflected off of it may be accomplished using a photodiode or other energy detecting mechanism. 
     Reflective layer  340 C and adhesion layer  350  may be combined in some embodiments. For example, in  FIG. 3C , reflective layer  340 C is positioned between structural support layer  320 C and ablatable protective-absorptive layer and may act as both a reflective layer that reflects energy from energy source  115  and as an adhesion layer that adheres the two adjacent layers. Thus, in some embodiments, the use of an adhesion layer is dependant on the type of reflective layer used or whether a reflective layer has been used. 
     Ablatable media  105  may also include protective layer  425 A. In some embodiments, a protective layer is added to provide protection for ablatable data layer  410 A. The protective layer may be optically opaque and is used at least partially for structural support and partially as a protective coating to prevent the data layer from being scratched or otherwise damaged. This protective layer may be added either before or after the recording process. 
     Ablatable media  105  may also include an absorptive layer  470 . Absorptive layer  470  may be added to ablatable media  105  to absorb ablatable material that is not entirely ablated during the ablation process. For example, when an energy source such as laser diode  502  is focused on one portion of ablatable data layer  310 A, all or a part of the ablatable material will be ablated at that point. Any material not entirely ablated may then be absorbed by absorptive layer  470 . In some embodiments, it may be advantageous to use a low density material with a stiff, foamed structure that allows remaining ablatable material to be absorbed. Examples of such materials include foamed nickel or Aspen Aerogel™. In some embodiments, protective layer  425 A and absorptive layer  470  may be combined into a single layer. These layers may be further combined with an ablatable data layer into ablatable protective-absorptive layer  330 C. 
     Although previously mentioned in part or in whole, each embodiment depicted in  FIGS. 3A-3D ,  4 A- 4 C and  7  will now be described. In some embodiments, ablatable media  301 A-D are used in combination with environment  500  in which ablation device  501  and laser diode  502  are positioned above structural support layer  525 . In alternative embodiments, ablatable media  401 A-C are used in combination with environment  600  in which ablation device  601  and laser diode  602  are positioned below structural support layer  625 . As mentioned above, the components of each of environments  500  and  600  may be placed horizontally, vertically, upside down or in any other geometric position with respect to the depictions in  FIGS. 5 and 6 . 
     Optimal orientation of the components may be determined by any one of a variety of factors. For example, the orientation of ablation device  501  to ablatable media  505  may depend on the intensity of laser beam  510 , the wavelength of laser beam  510 , the thickness of ablatable data layer  520 , the thickness of structural support layer  525  or the materials used to form any of the possible layers used in forming ablatable media  505 . The same is true for the orientation of ablation device  601  to ablatable media  605 . It should also be noted that the layers depicted in  FIGS. 3 ,  4  and  7  are not drawn to scale. Layer thicknesses and proportions in relation to other layers may be greater or smaller than those shown. Furthermore,  FIGS. 3 ,  4  and  7  do not depict all envisioned embodiments for ablatable media  301 / 401 / 701 . Other embodiments with different combinations of layers, using different materials for the various layers, and positioned in a variety of different positions are also possible. For example, any of ablatable media  301 / 401 / 701  may be used in combination with either or both of ablation devices  501  and  601 . 
       FIG. 3A  depicts ablatable media  301 A that includes ablatable data layer  310 A positioned on top of structural support layer  320 A. Ablated data points  315 A are shown in ablatable data layer  310 A as portions of ablatable material that have been removed by ablation. In discussing  FIGS. 3 ,  4  and  7 , it should be noted that the terms “top” and “bottom” as used herein refer only to the way in which the various embodiments are illustrated. Neither the terms “top” or “bottom,” nor the drawings necessarily imply that the media items will be used or fabricated in the manner shown. 
       FIG. 3B  depicts ablatable media  301 B that includes ablatable protective-absorptive layer  330 B positioned on top of structural support layer  320 B. Ablated data points  315 B are shown in ablatable protective-absorptive layer  330 B as portions of ablatable material that have been removed by ablation. 
       FIG. 3C  depicts ablatable media  301 C that includes ablatable protective-absorptive layer  330 C positioned on top of reflective layer  340 C, which is positioned on top of structural support layer  320 C. Similar to  FIG. 3B , ablated data points  315 C are shown in ablatable protective-absorptive layer  330 C as portions of ablatable material that have been removed by ablation. 
       FIG. 3D  depicts ablatable media  301 D that includes ablatable protective-absorptive layer  330 D positioned on top of reflective layer  340 D, which is positioned on top of adhesion layer  350 , which is positioned on top of structural support layer  320 D. Similar to  FIGS. 3B &amp; 3C , ablated data points  315 D are shown in ablatable protective-absorptive layer  330 D as portions of ablatable material that have been removed by ablation. 
       FIG. 4A  depicts ablatable media  401 A that includes protective layer  425 A positioned on top of reflective layer  440 A, which is positioned on top of ablatable data layer  410 A, which is positioned on top of structural support layer  420 A. Ablated data points  415 A are shown in ablatable data layer  410 A as positions of ablatable material that have been removed by ablation. 
       FIG. 4B  depicts ablatable media  401 B that includes protective layer  425 B positioned on top of reflective layer  440 B, which is positioned on top of ablatable data layer  410 B, which is positioned on top of adhesion layer  450 , which is positioned on top of structural support layer  420 B. Similar to  FIG. 4A , ablated data points  415 B are shown in ablatable data layer  410 B as positions of ablatable material that have been removed by ablation. 
       FIG. 4C  depicts ablatable media  401 C that includes protective layer  425 C positioned on top of reflective layer  440 C, which is positioned on top of ablatable data layer  410 C, which is positioned on top of absorptive layer  470 , which is positioned on top of structural support layer  420 C. Similar to  FIGS. 4A &amp; 4B , ablated data points  415 C are shown in ablatable data layer  410 C as positions of ablatable material that have been removed by ablation. Each layer has been assigned a unique identifier in order to further distinguish that each layer may be separately formed, may be formed of different materials, may be ablated in a different fashion, may be bonded differently, may be positioned differently, may have varying thicknesses or any other characteristic that may be modified. 
       FIG. 7  depicts ablatable media  701  that includes ablatable structural protective absorptive reflective layer  710  and ablated data points  715 . In some embodiments, layer  710  may be a single layer with one or more materials configured to provide an appropriate rigidity for ablatable media  701  and to provide ablatability such that one or more portions of layer  710  correspond to data points  715  that have been subject to ablation. It should be noted that, in some embodiments, ablation data points  715  do not proceed through the entire ablatable layer  710 . Instead the data points  715  occupy only a small portion of the total thickness of the layer  710 . For instance, when ablating a silicon wafer, in some cases the ablations are only a few dozen microns deep, whereas the remainder of the layer  710  is about 1200 microns (1.2 mm) thick. Other thicknesses and ablation depths may be used. Furthermore, the ablation depth of ablated data points  715  in  FIG. 7  is relative and can be changed to be deeper or shallower, depending on the material used and/or the energy used for ablation. 
     Ablated data points  715  correspond to digital data that is recordable on layer  710 . Ablatable media  701  may also include materials that are configured to provide protection for ablatable media  701 , reflection for reflecting ablation energy, and/or absorption for absorbing ablated material. In some cases, layer  710  may comprise a plurality of materials where each material is designed to perform one of the above-listed functions. In other cases, a single material may provide all, or at least a portion of, the above-listed functionality. 
     In one embodiment, a silicon wafer may be used as layer  710 . In this case, ablation would cause pits to form (ablated data points  715 ), as well as provide a sufficient optical contrast that data could be read from the media. The silicon wafer would provide structural rigidity, as well as protective, absorptive and reflective properties. In another embodiment, aluminum may be used in layer  710 . In such a case, ablation would cause pits to form (ablated data points  715 ), but may not provide a sufficient optical contrast. To provide additional contrast, the aluminum may be anodized and/or acid etched to darken the pits, thus providing increased optical contrast. Furthermore, similar to the silicon wafer, aluminum may provide structural rigidity as well as protective, absorptive and reflective properties for layer  710 . Although only aluminum and silicon were mentioned here, other single materials, such as glass, as well as other combinations of materials may be used to form layer  710 . 
     Returning now to  FIG. 2 , method  200  also includes an act of receiving digital data that is to be recorded on a recording layer of an optically ablatable digital storage media where the recording layer is formed on a substrate with zero or more intervening layers between the recording layer and the substrate, and where the recording layer includes ablatable material configured to store digital data (act  220 ). For example, digital data receiving module  135  may receive digital data  130  that is to be recorded on ablatable data layer  310 A of ablatable media  301 A. As explained above, the digital data can be in any data format or file type, can be compressed or uncompressed, encrypted or unencrypted and can comprise any number of bits. 
     Method  200  also includes an act of ablating the ablatable material in the recording layer according to a sequence defined by the received digital data such that the ablated portions correspond to data points of the received digital data (act  230 ). For example, ablation module  120  may communicate digital data  130  to energy source  115  such that energy source  115  can be used to ablate ablatable media  105  according to a sequence defined by digital data  130 . In some embodiments, energy source  115  is a laser diode. In such embodiments, optical energy may be used to ablate ablatable media  105  according to a sequence defined by digital data  130  such that the ablated portions correspond to data points of the digital data. 
     Thus, using the components and methods outlined in  FIGS. 1-7 , digital data may be permanently stored in ablated media  105 . The process of ablation is designed to leave indelible marks in the ablatable media that will be readable for hundreds of years, or more. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.