Page (File architecture): Difference between revisions
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A page is the underlying structure applied to the data | A page is the underlying structure applied to the data sets that comprise a Model 204 file. | ||
All pages are 6184 bytes. | All pages are 6184 bytes. | ||
When a file is [[Creating a | 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> | |||
==The 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> | |||
<li>The date/time when the individual page was last initialized.</li> | |||
<li>The date/time when the page was last written to the file.</li> | |||
<li>Data used in the [[CHECKPOINT command|checkpoint]] process.</li> | |||
<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> | |||
<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 | [[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:
Table Number FCT 00 Table A 01 Table B 02 Table C 03 Table D 04 Table E 40 Table X 20 - 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.