Abstract:
Disclosed is a holographic data storage device including holographic media for containing data, writing data to and reading data from. The storage device also includes at least one supplemental memory for containing at least a portion of a directory of the data contained in the holographic media. By locating directory information for the holographic media in a supplemental memory, areas of the holographic media that have not yet been written to can be determined prior to accessing the holographic media. In this way, activating photo-sensitive agents in unwritten areas of the holographic media can be avoided unless these areas are being written to.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to U.S. provisional patent application serial no. 60/440,862 files Jan. 15, 2003, which is hereby incorporated by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Holographic media is rapidly developing as a medium for mass storage of data. Because holographic media is capable of storing relatively large amounts of data it is necessary to be able to index holographic media to be able to locate specific data stored thereon and/or determine various parameters about the data and/or storage medium.  
           [0003]    One type of holographic storage device that includes holographic media is a cartridge that contains a spinning, circular disk having holographic media. Laser light can be projected onto the media to form holographic images in the media that contain data. When reading the holographic media, a reference laser beam illuminates the media to read out the holographic data.  
           [0004]    Often, any particular area of holographic media in such storage devices can be read many times but written to only once. That is, the media is “write-once” holographic media. It is also the case, however, that there is typically enough media space in such holographic storage devices that that a single device can be used for many storage sessions, with additional data being written to the holographic media during each session. For such multi-session use, it is important to index, or provide a directory for, data that is written to the media during each session. Such an index or directory includes information that allows particular data written to the media to be located on the media.  
           [0005]    For non-holographic media written to over multiple sessions, such directories are typically maintained in one of two ways. First, a session directory can be generated after each write session that indexes the data written to during that write session. Each of the session directories typically would include a pointer to the previous session directory. In order to locate information one the storage device, each session directory would be searched. A second way to index multi-session, non-holographic media is to generate a complete volume directory after each write session that includes an index of each of the sessions ever written to the disk. This can be accomplished by, after each write session, copying the previous volume directory and appending an index from the most recent write session.  
           [0006]    Each of these methods of maintaining a volume directory requires searching the media in the volume to be sure that all of the data has been indexed (either directly or with pointers) in the most recent directory. If a volume is not fully written to, this involves reading past the end of data stored in the media, that is reading into portions of the media that have not been written to, in order to be sure that all data has been indexed.  
           [0007]    Current storage devices can also allow the host to request reads beyond the end of data without checking the directory to see if data is present there. If there is no data or it does not pass a checksum, an error is returned.  
           [0008]    In storage devices using non-holographic media, this is not a significant issue. When using holographic media, however, reading into a portion of the media that has not been written to can present some difficulty. In particular, holographic media includes photosensitive agents that are activated when exposed to light. If areas of the media are exposed to a reference beam before being written to, the photo-sensitive agents in the media can be activated and the media&#39;s dynamic range, and thus storage capacity, can be undesirably reduced.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    Described herein is a holographic data storage device including holographic media for containing data, writing data to and reading data from. The storage device also includes at least one supplemental memory for containing at least a portion of a directory of the data contained in the holographic media. By locating directory information for the holographic media in a supplemental memory, areas of the holographic media that have not yet been written to can be determined prior to accessing the holographic media. In this way, activating photo-sensitive agents in unwritten areas of the holographic media can be avoided unless these areas are being written to. Also, the storage device can validate read requests from the host destined for unwritten areas and reject them before reading the media.  
           [0010]    It is also considered that the portion of the directory, such as a media map, be included in the holographic media and the portion of the directory on the supplemental memory include pointers to the portion of the directory in the holographic media. Additionally, the supplemental memory may include security information to prevent unauthorized access to the data in the holographic media as well as identification information for the holographic media.  
           [0011]    In another aspect of the present invention, a method of managing the contents of a holographic storage device includes storing data in a holographic media and storing at least a first portion of a directory for the data in the holographic media in a supplemental memory located adjacent to the holographic media. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a diagram of an exemplary holographic media cartridge which may include a supplemental memory in accordance with the present invention.  
         [0013]    [0013]FIG. 2 is a view of an end face of the media cartridge shown in FIG. 1 having a supplemental memory card mounted to an interior surface thereof in accordance with the present invention.  
         [0014]    [0014]FIG. 3 is a diagram of an exemplary supplemental memory card and supplemental memory card reader which can communicate via radio frequency signals in accordance with the present invention.  
         [0015]    [0015]FIG. 4 is a diagram of the holographic cartridge shown in FIG. 1 inserted into a holographic disk drive including a supplemental memory reader/writer in accordance with the present invention.  
         [0016]    [0016]FIG. 5 is a flow diagram illustrating a method of writing data to holographic media using a directory on a supplemental memory in accordance with the present invention.  
         [0017]    [0017]FIG. 6 is a flow diagram illustrating a method of reading data from holographic media using a directory using a directory on a supplemental memory in accordance with the present invention.  
         [0018]    [0018]FIG. 7 is a diagram of an exemplary supplemental memory card including electrical contact pads for use in accordance with the present invention.  
         [0019]    [0019]FIG. 8 is a diagram of a end portion of a holographic storage cartridge including a supplemental memory card as shown in FIG. 7.  
         [0020]    [0020]FIG. 9 is a diagram of a hand-held device including a supplemental memory card reader using radio frequency signals to read a supplemental memory of a holographic storage cartridge stored in a cartridge warehouse in accordance with the present invention.  
         [0021]    [0021]FIG. 10 is a diagram of a jukebox including a supplemental memory storing a plurality of holographic storage cartridges including a supplemental memory card reader for reading a supplemental memory of each storage cartridge in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    [0022]FIG. 1 illustrates an example of a storage cartridge  100  containing holographic media that data can be written to and read from. Storage cartridge  100  includes a housing  110 , which can be formed from metal, plastic or other rigid material. Housing  110  contains circular holographic media  112  mounted on a spindle  114  to allow holographic media  112  to spin inside of housing  110 . As is understood by those skilled in the art, holographic media  112  includes photosensitive agents which allow holograms to be recorded therein, as is well understood in the art. Examples of holographic media suitable for use in a cartridge  100  are disclosed, for example, in U.S. Pat. Nos. 6,103,454 and 5,932,045 which are both hereby incorporated by reference in their entirety. Cartridge  100  also includes a shutter  116  that can close over an opening  118  in cartridge  100 . Opening  118  allows media  112  to be accessed by a light beams to generate holograms in media  112  and read holograms therefrom when shutter  116  is in the open position (as shown in FIG. 1). Shutter  116  can also be closed to cover and protect holographic media  112 . Cartridges including holographic media are known in the art and disclosed, for example, in H. J. Coufal et. al, Holographic Data Storage C. Springer-Verlag 2000, p.349-49, which is hereby incorporated by reference herein in its entirety. Holographic drives suitable for reading holographic media in cartridge  100  is disclosed, for example, in commonly owned U.S. patent application Ser. No. 10/146,085 for “Method and Apparatus for Phase Correlation Holographic Drive”, and H. J. Coulfal et. al, Holographic Data Storage C. Springer-Verlag 2000, pp. 343-357 and 399-407 both of which are hereby incorporated by reference in their entirety. Cartridge  100  is only an exemplary storage cartridge that can be used in accordance with the present invention. It is considered that any data storage device including holographic media may be used in accordance with the present invention.  
         [0023]    As shown in FIG. 1, cartridge  100  includes an end face  120  opposite to the end face of cartridge  100  including opening  118 . FIG. 2 illustrates end face  120  of cartridge  100 . Preferably, as shown, a radio frequency identification (“RFID”) board  200  is mounted, using any appropriate adhesive or by any other means, at the interior of end face  120 . FIG. 3 illustrates a preferred embodiment of RFID board  200  and RFID reader card  230  which can both read from and write to RFID board  200 . Board  200  includes an RFID chip  210  and a coil  220 , which acts as an antennae, interconnected with RFID chip  210 .  
         [0024]    RFID chips such as RFID chip  200  are well known in the art and can include, as shown in FIG. 3, a memory section  212 , a power section  214 , a control section  216  and an RFID antenna  218 . Power section  214  provides power to memory section  212  and control section  216 . Control section  216  controls where data is written to and read from in memory section  212  and memory section  212  stores the data. Memory section  212  is preferably a non-volatile memory such as flash memory, EEPROM, or any other non-volatile memory. Memory section  212  preferably includes from  64  bytes to  256  bytes but may be either larger or smaller. RFID card preferably includes a coil  220  interconnected with RFID antenna  218  to boost signal strength of both transmitted and received signals. RFID antenna  218  receives data to be stored in memory section  212  from coil  220  and provides data stored in memory section  212  to coil  220 . Coil  220  wirelessly receives data to be stored in memory section  212  via RF signals  21 . 5  from a reader antenna  236  of reader card  230  and wirelessly transmits data read from memory section  212  via RF signals  215  to reader antenna  236 .  
         [0025]    Reader card  230  includes a controller  232 , transceiver  234  and, as noted above, reader antenna  236 . Data to be written to memory section  212  of RFID card  200  is fed into controller  232  which feeds the data into transceiver  234  and controls the operation of transceiver  234  to either transmit data to be written to memory section  212  or receive data read from memory section  212  via RF signals  215  to and from reader antenna  236 . When data is to be read from memory  212 , controller  232  directs transceiver  234  to access memory section  212  via reader antenna  236  and control section  216  to read data from memory section  212 . RFID chips, such as RFID chip  200  and RFID readers such as reader card  230 , and reading and writing data to and from RFID chips using an RFID reader is well understood in the art. RFID chips and RFID readers are commercially available from, for example, Maxell Corporation of America having offices in Colorado and New Mexico. One example of a RFID chip that can be used with the present invention is available from Maxell® Corporation of America under the designation ME-Y1001. One example of an RFID reader card that can be used with the present invention is available from Maxell® Corporation of America under the designation “Picochet”.  
         [0026]    [0026]FIG. 4 illustrates holographic storage cartridge  100  inserted into a disk drive  300 . The details of the holographic writing and reading apparatus in disk drive  300  have been omitted for clarity. As noted above, apparatuses and methods for writing and reading holographic data to and from holographic media are well understood in the art. As discussed above, storage cartridge  100  includes holographic media  112  rotating on a spindle  114  and RFID card  200 . Disk drive  300  includes a drive controller  310  which is connected to an external data source/sink  316  which may be, but need not be, a standard PC. Disk drive  300  also includes RFID reader  230 . External data source/sink  316  provides data to be stored in storage cartridge  100  by disk drive  300 . This data is provided to drive controller  310  which in turn, as will be discussed in detail below, provides it to holographic read/write control  312 . As is understood in the art, holographic read/write control  312  controls holographic optics (not shown) to write the provided data to holographic media  112 . Data can also be requested from storage cartridge  112  by external data source/sink  316  via drive controller  310 . When data is requested, as will be discussed in detail below, drive controller  310  provides addressing information to data read/write control  312  to retrieve the requested data and provide it, via drive controller  310 , to external data source/sink  316 . As will be discussed in detail below, RFID reader  230  provides directory information to and reads directory information from RFID card  200 , that is it accesses RFID card  200 , in cartridge  100 .  
         [0027]    [0027]FIG. 5 is a flow chart illustrating a one embodiment of a method  350  of writing data to media  112  of cartridge  100 . Cartridge  100  is preferably inserted into drive  300  and data source  316  makes a write request for data to drive controller  310 . In step  352 , drive controller  310  activates reader  230  to read directory information from RFID card  210 . Drive controller  310  then stores this directory information, preferably in RAM (not shown) available to controller  310 , in drive  300 . This step is preferably carried out only once after a cartridge  100  is placed into drive  300 . The directory information stored, and updated, in drive  300  is then used for subsequent reads and writes. In step  354 , based on the directory information received from RFID card  210 , it is determined in controller  310  what areas of media  112  are not yet written to. This step advantageously can allow areas of media  112  not yet written to avoid being exposed to a reference beam which would, as discussed above, undesirably reduce the storage capacity of media  112 . Directory structures for providing a physical location for data on a storage device are well understood in the art and typically include a media map, which provides a physical location for all data on a disk. In accordance with the present invention, the media map may either be located in the memory  212  of RFID card  210 , or memory  212  may simply include pointers to the location of the media map which may be stored in holographic media  112 . Pointers to a disk location are also well understood in the art. In step  356 , controller  310  accesses holographic data read/write control  312  to write the data provided by data source/sink  316  to media  112 . In step  358 , controller  310  accesses RFID reader  230  to update directory information, discussed further below, contained in RFID card  200 . As is understood in the art, such updating may include either rewriting the entire directory structure or may include just appending the directory information from the most recent write to the preexisting directory structure. Controller  310  can also update the version of the directory acquired in step  352  and stored in RAM (not shown) of drive  300 .  
         [0028]    [0028]FIG. 6 is a flow chart illustrating one embodiment of a method  370  of reading data from cartridge  100 . Cartridge  100  is preferably inserted into drive  300  and data source  316  makes a read request for data to drive controller  310 . In step  372 , drive controller  310  activates reader  230  to read directory information from RFID card  210 . Drive controller  310  then stores this directory information, preferably in RAM (not shown) available to controller  310 , in drive  300 . This step is preferably carried out only once after a cartridge  100  is placed into drive  300 . The directory information stored, and updated, in drive  300  is then used for subsequent reads and writes. In step  374  it is determined in controller  310  what areas of media  112  are not yet written to. This step advantageously can allow areas of media  112  not yet written to avoid being exposed to a reference beam which would, as discussed above, undesirably reduce the storage capacity of media  112 . Directory structures for providing a physical location for data on a storage device are well understood in the art and typically include a media map, which provides a physical location for all data on a disk. In accordance with the present invention, the media map may either be located in the memory  212  of RFID card  210 , or memory  212  may simply include pointers to the location of the media map which may be stored in holographic media  112 . Pointers to a disk location are also well understood in the art. In step  376 , controller  310  uses the retrieved directory information to determine the location on media  112  of the data requested by data source/sink  316 . It is then determined, in step  378 , whether the request was to read an area of the media that has not yet been written to. If this is the case, then in step  380 , the media is not accessed and an error message is returned to data source/sink  316 . This prevents un-written areas of the media from be accessed by a request to access such an area. If the request is to read an area of the disk that has been written to, then, in step  382 , the requested data is read from media  112 . Because the directory information was acquired from RFID card  200 , this can be accomplished without exposing to a reference beam any areas of media  112  that have not yet been written to.  
         [0029]    Communication protocols between data source/sink  316 , controller  310 , holographic data read/write control  312 , RFID reader  230  and RFID card  200  for carrying out methods  350  and  370  are well understood in the art. Additionally, data structures for indexing the location of data on media  112  are also well understood in the art and discussed further below.  
         [0030]    It is also within the ambit of the present invention to use an EEPROM memory as the supplemental directory that makes mechanical contact with a reader in a drive rather than radio frequency contact. FIG. 7 illustrates a supplemental memory board  400  including an EEPROM chip  410  mounted on a rear side of the board and  5  contact pads  412 ,  414 ,  416 ,  418  and  420  which are connected, as described below, with the pins of EEPROM chip  410 . In the example shown, EEPROM chip  410  includes  8  pins. Address pins A 0 , A 1  and A 2  are preferably not used. Ground pin GND is connected to pad  420 , serial data pin SDA is connected to pad  418 , serial clock input pin SCL is connected to pad  416 , write protect pin WP is connected to pad  414  and power pin Vcc is connected to pad  412 . The use and configuration of pins GND, SDA, SCL, WP and Vcc for accessing and controlling EEPROM chip  410  are well understood in the art. EEPROM chip such as EEPROM chip  410  are available from Atmel® Corporation, of San Jose, Calif. under the designation AT24C32A and AT24C64A.  
         [0031]    [0031]FIG. 8 illustrates a preferred method for including supplemental memory board  400  into a holographic storage cartridge  100 ′, which can be substantially similar to storage cartridge  100  discussed above. Storage cartridge  100 ′ includes a rear face  120 ′ having 5 openings,  150 ′,  152 ′,  154 ′,  156 ′ and  158 ′ in an upper edge thereof. Supplemental memory chip  400  can be mounted to the interior surface of rear face  120 ′ such that pad  412  is exposed through opening  150 ′, pad  414  is exposed through opening  152 ′, pad  416  is exposed through opening  154 ′, pad  418  is exposed through opening  156 ′ and pad  420  is exposed through opening  158 ′. In this way, pins located in a holographic disk drive reader such as disk drive  300  discussed above can contact pads  412  through  420  to control, and write and read data to and from EEPROM chip  410 . Such control and writing and reading of data to EEPROM chips is well understood in the art. It is also considered that any other wireless forms of communication other than radio frequency signals may be used to allow an RFID card to be accessed by an RFID reader. Such forms of wireless communication can include, without limitation, optical communication.  
         [0032]    A supplemental memory, such as included in RFID card  200 , located in a storage cartridge, such as storage cartridge  100 , may also be employed in applications other than those involving a single cartridge disk drive, such as disk drive  300 . For example, it is considered that a supplemental memory be read by a hand-held reader. FIG. 9 illustrates a hand held RFID reader  500  reading data via RF signals  512  off RFID card  200  located in holographic storage cartridge  100  which may be located in a warehouse  105  of holographic storage cartridges  102  similar to cartridge  100 . Hand held RFID readers are well known in the art and available, for example, from Opticon, Inc. of Orangeburg, N.Y. under the designation PHL-2700 RFID. By using hand held RFID reader  500 , the contents and state of media  112  in cartridge  100  can be determined without inserting cartridge  100  into a holographic disk drive or other readout device. This allows an inventory of the media currently available in a storage library or warehouse  100  or on shelves outside of a warehouse to be obtained without excessive handling of the media. Searches for specific volumes or data in a cartridge, such as cartridge  100 , can be executed without physically accessing a cartridge. This can reduce data search and access times in warehousing and large data store applications. For example, handheld RFID reader  500  is used to read identification information from a plurality of holographic storage cartridges  102 . Each cartridge preferably includes an RFID card such as RFID card  200  shown in FIG. 3. As discussed below in detail, the memory portion of each RFID card can include a keyword field having a keyword which provides some identification information for the data contained in the holographic media of a cartridge  102 . For example, short descriptions of video clips or keywords or dates to help determine if the media has the desired information.  
         [0033]    It is also considered that an RFID card and reader be used in a jukebox application. FIG. 10 illustrates a jukebox  600  for storing and reading holographic storage cartridges  612 . Such jukeboxes are well known in the art and include at least one holographic disk drive  610 , a conveyor mechanism  614  and tray  616  for transporting selected cartridges from a storage location to disk drive  610 . Holographic storage cartridges  612  can be substantially the same as storage cartridge  100  discussed above, and include an RFID card (not shown) such as RFID card  100 , also discussed above. In the embodiment shown, tray  616  includes an RFID reader  618 , which can be substantially the same as RFID reader  230  discussed above. As is understood in the art, in operation, tray  616  is driven along a stack of cartridges  612  by conveyor mechanism  614 . When a specific cartridge is desired to be read, a jukebox controller (not shown) directs tray  616  to remove the cartridge from the stack and place it in disk drive  610  to be read. By including an RFID card in each cartridge  612  and an RFID reader in tray  616 , an inventory of the media available in jukebox  600  can be obtained without inserting a cartridge  612  into disk drive  610 . This can simplify inventory and management of cartridges in jukebox  600  as searches for specific volumes or data, as well as the state media (e.g. full or not), can be determined without placing a cartridge  612  into disk drive  610 .  
         [0034]    Exemplary Volume Directory Structure  
         [0035]    Table 1 below illustrates an exemplary directory structure that may be stored in the memory section of the RFID card in accordance with the present invention.  
                                               TABLE 1                           Volume Directory Definition            Structures   Field   Size                    Basic   Volume Directory ID   32   bits       Information   Volume Directory Length in Bytes   16   bits           Volume Directory Revision   8   bits           Volume Directory Sequence Number   8   bits           Total Bytes in this portion of the Volume   32   bits           Directory           Address Pointer to Media Based Volume   32   bits           Directory           Pointer to Redundant Copy of Media Based   32   bits           Volume Directory           Pointer to Previous Media Based Volume   32   bits           Directory           Format Generation   8   bits           Media Geometry Code   8   bits           Media Formulation Code   8   bits           Media Status   8   bits           Volume ID Size   8   bits           Volume ID Field   256   Bytes           Overall Drive Statistics Size   8   bits           Overall Drive Statistics Field   256   Bytes           Security/Copyright Information   32   Bytes           Overall Search Key Size   16   bits           Search Key Fields   1024   Bytes           Media Map Location   8   bits           Pointer to Most Recent Media Map   32   bits           Next Appendable Address   23   bits           Volume Directory CRC   16   bits                  
 
         [0036]    Below are further explanations for the volume directory fields.  
         [0037]    The Volume Directory ID is a unique pattern to identify the start of the volume directory structure.  
         [0038]    The Volume Directory Length is the length in bytes from the start of the volume directory through volume directory cyclic redundancy code, which is for error checking and appears at the end of the directory.  
         [0039]    The Volume Directory Revision is the version of this volume directory header.  
         [0040]    The Volume Directory Sequence Number starts at 0 and is incremented each time the Volume Directory is updated.  
         [0041]    The Total Bytes in This Portion of the Volume Directory is the number of bytes beginning with the volume directory ID field that are included in this structure including all attached media map information. As is well understood in the art, media map information provides the actual physical coordinates of data on the media. This field is used in case all of the information cannot fit in the supplemental memory and some information must be placed on the media.  
         [0042]    The Address Pointer to Media Based Volume Directory points to the area where the current volume directory information is repeated in full if the volume directory and media map do not fully fit in the supplemental memory. It is a physical address on the media specifying the coordinates of the data.  
         [0043]    The Pointer to Redundant Copy of Remainder of the Volume Directory is provided so that if desired, two copies of the volume directory may be written to the media in different locations on the media. This is also a physical address.  
         [0044]    The Pointer to Previous Media Based Volume Directory: It is considered that the supplemental memory contains directory information that includes a volume directory having a full or partial media map. It is also considered that the supplemental memory contain directory information that contains just pointers to locations on the media where a volume directory containing a full media map are located. If there are volume directories written on the media, a new version is written after each write session. This field points to the location of the media where the previous volume directory is located. This allows the drive to examine old volume directories for a history of how the media has been written.  
         [0045]    The Format Generation field provides a definition of the format implementation for the media and directory.  
         [0046]    The Media Geometry Code provides physical information about the media not including its formulation. Items encoded in this can include, without limitation, disk versus coupon, in a cartridge or not, if it has an addressing servo pattern and, if so, what kind/version, substrate type, and guard bands.  
         [0047]    The Media Formulation Code provides information about the media formulation. The formulation information can include, without limitation, thickness of the media, formulation type, write once versus rewritable, and any other information needed to determine capacity, write schedules, and cure times.  
         [0048]    The Media Status indicates if the media has never been written, is partially written, is appendable, full, or write protected. Table 2 below indicates how this field is encoded.  
                                                                                   TABLE 2                           MEDIA STATUS BYTE DEFINITION                7   6   5   4   3   2   1   0                            Formatted   Secure   Reserved       Status                          
 
         [0049]    If the Formatted field is 0, then the disk is unformatted and if the Formatted field is I then the disk is formatted. If the Secure field is 0 then anyone can read the disk and if the Secure field is I the some security policies will be used to determine readability of the data.  
         [0050]    The Status Field provides the current overall status of the media as follows:  
         [0051]    0=Empty—never been used  
         [0052]    1=Appendable—Has been written and can still be added to  
         [0053]    2=Write Protected—User has write protected the cartridge  
         [0054]    3=NonAppendable—Some recovery error or write timeout occurred on the media and it can no longer be written to. It is not full and may not be cleanly finished.  
         [0055]    4=Full—Media has been written to capacity and cured  
         [0056]    The Volume ID Size is the Number of bytes in the volume ID field.  
         [0057]    The Volume ID is an ASCII string created by the user to identify the volume. This field preferably has a maximum length of 256 bytes. It may be may shorter, or zero, however.  
         [0058]    The Overall Drive Statistics Size is the number of bytes in the drives statistics field (below). The maximum size is preferably 256 bytes, but may be shorter.  
         [0059]    The Overall Drive Statistics Field maintains overall stats like serial numbers for the drives that have written the media and can include, without limitation, the number of read/write/load/unload cycles, and time parameters that may help determine overall media life.  
         [0060]    The Security/Copyright Information field can be used for secure access via passwords and encrypted security key codes and to keep track of copyright protection. It may be used to prevent unauthorized reading and/or copying of the data.  
         [0061]    The Overall Search Key Size is the number of bytes in the search key fields (discussed below).  
         [0062]    Search Key Fields: Multiple search keys can be located here to allow for a quick way to determine what specific data resides on the media. This can be any type of metadata that is specific to an application. An example is short descriptions of video clips or keywords or dates to help determine if the media has the desired information. The field definitions are defined by the format generation.  
         [0063]    Media Map Location: As is understood in the art, the media map provides a detailed mapping between host logical blocks and physical structures on the media. It may reside in the supplemental memory directly succeeding the volume descriptor or it may be located on the media. A detailed description of an exemplary media map is provided below. The defined values are:  
         [0064]    0=No Map  
         [0065]    1=Map directly succeeds this volume descriptor  
         [0066]    2=Map is on the media  
         [0067]    The Pointer to Most Recent Media Map field allows the drive to find the media map. The meaning of the field depends on the map location field as follows:  
         [0068]    If there is no map, this field=0.  
         [0069]    If the map follows the volume directory, this is the number of bytes from the start of this volume directory to the start of the map.  
         [0070]    If the map is on the media, this is the physical address of the most recent map written.  
         [0071]    Volume Directory CRC—This CRC covers the full structure of the fields listed in Table 1. It is a CRC-16 format with polynomial x 15 +x 2 +1. If this fails, it is assumed this copy of the volume directory is bad.  
         [0072]    An exemplary definition of a media map is shown below in Table 3.  
                             TABLE 3                           Media Map Definition            Structures   Field   Size               Media Map   Media Map ID   32 bits       Header   Media Map Header Length in Bytes    8 bits           Media Map Revision    8 bits           Media Map Starting Book Address   32 bits           Total Number of Entries in Media Map   16 bits           Size of each Media Map Entry   16 bits           Media Map Header CRC   16 bits       Media Map   Media Map Entry Header   16 bits       Entries   Status Byte    8 bits       (1 per physical   Reserved    8 bits       address)   Physical Book Address   32 bits           Number of Holograms written at this   16 bits           physical address           Hologram number of the start of the first new   16 bits           logical block address at this physical address.           First Logical Block Address starting at this   32 bits           physical address       Media Map   CRC over entire Media Map structure   16 bits       Footer                  
 
         [0073]    Further description of each field appears below.  
         [0074]    Media Map Header Definitions:  
         [0075]    The Media Map ID is a unique pattern that identifies the start of a media map data structure.  
         [0076]    The Media Map Header Length in Bytes is the number of bytes in the media map header including the ID and CRC.  
         [0077]    The Media Map Revision is the Revision number of this media map.  
         [0078]    The Media Map Starting Book Address is the first physical book address that has a media map entry contained in this media map structure. There may be multiple media map structures used to describe all of the written media. An example would be for multi-session writes where a new media map structure is created each time a write session is completed.  
         [0079]    The Total Number of Media Map Entries is the number of Media Map entries that immediately follow the Media Map Header structure.  
         [0080]    The Size of Each Media Map Entry is the Size in bytes of each Media Map entry that follows.  
         [0081]    The Media Map Header CRC is a 16 bit CRC of the Media Map header to check the validity of the contents. This is the same CRC method used for the Volume Directory structure.  
         [0082]    Media Map Field Definitions:  
         [0083]    The Media Map Entry Header identifies the start of a Media Map entry.  
         [0084]    The Media Map Status Byte describes the status and contents of the information at this physical address as shown below in Table 4.  
                                             TABLE 4                                       Bit                    7(msb)-5   4-3   2-0 (lsb)                       Def   Reserved = 0   Density   Status                      
 
         [0085]    Density: 0=Written at full density for this format type.  
         [0086]    1=Written at low density for this format type.  
         [0087]    2-3=Reserved  
         [0088]    Status: 0=Unused/Unexposed  
         [0089]    1=Partially Filled  
         [0090]    2=Fully Filled/Cured  
         [0091]    3=Mapped Out-Bad  
         [0092]    The Physical Address is the address of the media being described by this entry.  
         [0093]    The Number of Holograms Written at this Physical Address is the number of data holograms recorded at this address. This does not include filler data used to used up the media&#39;s capacity at this address. This allows for a variable number of holograms to be written at each physical location.  
         [0094]    The Hologram Number of the Start of the First New Logical Block Address at this Physical Address is the first hologram number at this physical address containing data that starts a new logical block address. The logical block address is the address requested by the host for reading.  
         [0095]    The CRC For Entire Media Map Structure is a 16 bit CRC over the entire Media Map including the header and all media map entries. The same CRC polynomial is used as for the Volume Directory. The Media Map is invalid if the CRC fails.  
         [0096]    It is to be understood that the exemplary directory structure discussed above and shown in Tables 1, 2 and 3 is only one example of a directory structure that may be used in implementation of the present invention. Any type of directory structure that provides information about the location of data on corresponding holographic media is contemplated for use with the present invention. For example, the directory structure discussed above uses pointers to indicate the location of a full media map located on the holographic media. A full or partial media mapping table may also be included in the RFID memory section.  
         [0097]    The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and it should be understood that many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. Many other variations are also to be considered within the scope of the present invention.