file : filehdr.text
date : 24-Feb-1983

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::::::::       First Pass from Karl and me             ::::::::::
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Block pointers are 24 bits.
Nil block pointers equal 0.
End and beginning of a list specified by a nil block pointer.


        File Header

 +-------------------------------------+  <<--+
 | header info - 28 bytes    ???       |      |
 |---------+---------------------------|      |
 | record  |   Block pointer to        |      |
 | count   |   secondary index block   |      |
 |---------+---------------------------|      |
 | 2 bytes +  4 bytes  = 6 bytes       |      |-- first primary
 |                                     |      |-- index block
 |               .    total of         |      |-- file header blk
 |               .    80 secondary     |      |
 |               .    index block      |      |
 |                    pointer records  |      |
 |                                     |      |
 |                                     |      |
 |                                     |      |
 |                                     |      |
 |-------------------------------------|      |
 |  pointer to next primary index blk  |      |
 |     - 4 bytes                       |      |
 +-------------------------------------+  <<--+

  File header info :  must be defined
       type, user name, protection,
       fixed or variable records
       max record length ???
 .PG

       Primary Index block - not header block

 +-------------------------------------+  <<--+
 |  ptr to file header block  4 bytes  |      |
 |-------------------------------------|      |
 |  ptr next primary index blk 4 bytes |      |
 |-------------------------------------|      |
 |  ptr prev primary index blk 4 bytes |      |
 |-------------------------------------|      |
 | record  |   Block pointer to        |      |
 | count   |   secondary index block   |      |
 |---------+---------------------------|      |-- next primary
 |               .    total of         |      |-- index block
 |               .    83 secondary     |      |
 |               .    index block      |      |
 |                    pointer records  |      |
 |                                     |      |
 |                                     |      |
 |                                     |      |
 |                                     |      |
 |-------------------------------------|      |
 | 2 bytes unused ?????                |      |
 +-------------------------------------+  <<--+


  Secondary index block pointer records :

       2 byte count of records available from secondary
              index block
       4 byte pointer to a secondary index block
              This is a block pointer.  The hi order byte
              is always zero (0).

.PG

       Secondary index block

 +-------------------------------------+
 |  ptr to file header block  4 bytes  |
 |-------------------------------------|
 |  ptr next scndary index blk 4 bytes |
 |-------------------------------------|
 |  ptr prev scndary index blk 4 bytes |
 |-------------------------------------|
 | record  |   Block pointer to        |
 | count   |   data block              |
 |---------+---------------------------|
 | 1 byte  +  3 bytes = 4 bytes        |
 |                                     |
 |               .    total of         |
 |               .    123 data block   |
 |               .    pointer records  |
 |                                     |
 |                                     |
 |                                     |
 |                                     |
 +-------------------------------------+


 Data block pointer record :

       1 byte unsigned integer, count of records in
              data block.
       3 byte pointer to a data block.  A block pointer.



.PG

       Data block

 +-------------------------------------+
 |  ptr to file header block  4 bytes  |
 |-------------------------------------|
 |  pointer next data block   4 bytes  |
 |-------------------------------------|
 |  pointer prev data block   4 bytes  |
 |-------------------------------------|
 |                                     |
 |                                     |
 |         500 bytes of data           |
 |                                     |
 |                                     |
 |     variable length records         |
 |                                     |
 |                                     |
 |                                     |
 |                                     |
 |                                     |
 |                                     |
 +-------------------------------------+



  variable length records :

       1 unsigned byte, data length
       n bytes data

  Data can be read in sequential stream fashion by
  chaining through data block list from beginning
  to end.