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<p>to the point where they can be <a href="page.php?w=Library_%28computing%29">loaded in and out as needed</a>.</p>

<p><big>Historical use</big></p>
<p>IBM introduced the concept of a <a href="page.php?w=chain_job">chain job</a>in <a href="page.php?w=FORTRAN_II">FORTRAN II</a>. The program had to explicitly call the CHAIN subroutine to load a new link,and the new link replaced all of the old link's storage except for the Fortran COMMON area.</p>

<p>IBM introduced more general overlay handling in <a href="page.php?w=IBSYS">IBSYS</a>/<a href="page.php?w=IBJOB">IBJOB</a>,</p><p>
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