Page (File architecture): Difference between revisions

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All pages are 6184 bytes.
All pages are 6184 bytes.


When a file is [[Creating a file (File management)|created]], the pages in the file are formatted into:
When a file is [[Creating a file|created]], the pages in the file are formatted into:
<ul>
<li>6144 bytes of "usable" space (how the space is used depends on the table where the page resides)
<li>A 40-byte page trailer
</ul>


* 6144 bytes of 'usable' space (how the space is used depends on the table where the page resides)
==The page trailer==
* a 40 byte page trailer
The page trailer contains the following:
<ul>
<li>The file name, which is the name used in the [[CREATE command: File|create]] process.</li>


== The page trailer ==
<li>The date/time when the individual page was last initialized.</li>


The page trailer contains:
<li>The date/time when the page was last written to the file.</li>


* the file name, which is the name used in the [[CREATE command: File|create]] process
<li>Data used in the [[CHECKPOINT command|checkpoint]] process.</li>
* the date / time when the page was last [[INITIALIZE command|initialized]]
* the date / time when the page was last written to the file
* data used in the [[CHECKPOINT command|checkpoint]] process
* the table that this page is part of (a numeric representation as explained in Note 1 below)
* the sequential page number within the table


Note 1: FCT = 00, Table A = 01, Table B = 02, Table C = 03, Table D = 04, Table E = 40 and Table X = 20.
<li>The table that this page is part of, the numeric representation for which is as follows:
<table>
<tr class="head"><th>Table</th><th>Number</th></tr>


Because of INCREASE and DECREASE commands after the initial CREATE, the pages for a table might not be contiguous. 
<tr><td>FCT</td><td>00</td></tr>
<tr><td>Table A</td><td>01</td></tr>
<tr><td>Table B</td><td>02</td></tr>
<tr><td>Table C</td><td>03</td></tr>
<tr><td>Table D</td><td>04</td></tr>
<tr><td>Table E</td><td>40</td></tr>
<tr><td>Table X</td><td>20</td></tr>
</table></li>


<li>The sequential page number within the table; a three-byte binary integer.
<p>
Because of <var>[[INCREASE command|INCREASE]]</var> and <var>[[DECREASE command|DECREASE]]</var> commands after the initial <var>CREATE</var>, the pages for a table might not be contiguous.</p></li>
</ul>


[[Category:File architecture]]
[[Category:File architecture]]

Latest revision as of 23:37, 5 March 2015

A page is the underlying structure applied to the data sets that comprise a Model 204 file.

All pages are 6184 bytes.

When a file is created, the pages in the file are formatted into:

  • 6144 bytes of "usable" space (how the space is used depends on the table where the page resides)
  • A 40-byte page trailer

The page trailer

The page trailer contains the following:

  • The file name, which is the name used in the create process.
  • The date/time when the individual page was last initialized.
  • The date/time when the page was last written to the file.
  • Data used in the checkpoint process.
  • The table that this page is part of, the numeric representation for which is as follows:
    TableNumber
    FCT00
    Table A01
    Table B02
    Table C03
    Table D04
    Table E40
    Table X20
  • The sequential page number within the table; a three-byte binary integer.

    Because of INCREASE and DECREASE commands after the initial CREATE, the pages for a table might not be contiguous.