https://gunkies.org/index.php?action=history&feed=atom&title=OverlayOverlay - Revision history2026-09-24T19:43:55ZRevision history for this page on the wikiMediaWiki 1.43.9https://gunkies.org/w/index.php?title=Overlay&diff=37162&oldid=prevJnc: /* See also */ +PDP-11 Unix overlays2026-09-07T09:51:17Z<p><span class="autocomment">See also: </span> +PDP-11 Unix overlays</p>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Overlays perform the same basic function as the later [[virtual memory]] ('jam three gallons into a one-gallon bucket'), but do so explicitly, not automatically and invisibly.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Overlays perform the same basic function as the later [[virtual memory]] ('jam three gallons into a one-gallon bucket'), but do so explicitly, not automatically and invisibly.</div></td></tr>
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<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>==<del style="font-weight: bold; text-decoration: none;">External links</del>==</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>==<ins style="font-weight: bold; text-decoration: none;">See also</ins>==</div></td></tr>
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<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>* [<del style="font-weight: bold; text-decoration: none;">https://minnie.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/man/man5/a.out.5 a.out (5)] - this and the next entry describe the supports for overlays in the later </del>PDP-11 <del style="font-weight: bold; text-decoration: none;">[[BSD]]s</del></div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>* [<ins style="font-weight: bold; text-decoration: none;">[</ins>PDP-11 <ins style="font-weight: bold; text-decoration: none;">Unix </ins>overlays]]</div></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">* [https://minnie.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/man/man1/ld.1 ld (1)]</del></div></td><td colspan="2" class="diff-side-added"></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">* [https://minnie.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/doc/2.9_kernel.ms Changes in the Kernel in 2.9BSD] - describes use of </del>overlays <del style="font-weight: bold; text-decoration: none;">in the [[2.9BSD]] [[kernel</del>]]</div></td><td colspan="2" class="diff-side-added"></td></tr>
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</table>Jnchttps://gunkies.org/w/index.php?title=Overlay&diff=26810&oldid=prevJnc: Jnc moved page Broadcast to Overlay without leaving a redirect: Bah, created at wrong name2022-06-30T16:03:49Z<p>Jnc moved page <a href="/wiki/Broadcast" title="Broadcast">Broadcast</a> to <a href="/wiki/Overlay" title="Overlay">Overlay</a> without leaving a redirect: Bah, created at wrong name</p>
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</table>Jnchttps://gunkies.org/w/index.php?title=Overlay&diff=26809&oldid=prevJnc: Next top entry on 'Wanted pages' for me2022-06-30T16:03:04Z<p>Next top entry on 'Wanted pages' for me</p>
<p><b>New page</b></p><div>'''Overlays''' are a [[programmer|programming]] technique for dealing with reduced availability of [[main memory]] - either because of a limited [[address space]] (as in the [[PDP-11]], towards the end of its life), or because the machine just did not have much (very common in the early days of computers).<br />
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The program to be 'overlaid' was split up into tranches, called 'overlays', of which only one (or a limited number) were directly available to the [[Central Processing Unit|CPU]] at a time. When the program needed to transfer (via either a [[jump]], or a [[subroutine]] call) to an overlay that was not currently accessible, progress had to stop momentarily while that overlay was made accessible (perhaps by reading it in from [[secondary storage]]).<br />
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Overlays perform the same basic function as the later [[virtual memory]] ('jam three gallons into a one-gallon bucket'), but do so explicitly, not automatically and invisibly.<br />
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==External links==<br />
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* [https://minnie.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/man/man5/a.out.5 a.out (5)] - this and the next entry describe the supports for overlays in the later PDP-11 [[BSD]]s<br />
* [https://minnie.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/man/man1/ld.1 ld (1)]<br />
* [https://minnie.tuhs.org/cgi-bin/utree.pl?file=2.9BSD/usr/doc/2.9_kernel.ms Changes in the Kernel in 2.9BSD] - describes use of overlays in the [[2.9BSD]] [[kernel]]<br />
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[[Category: Software Concepts]]</div>Jnc