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<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta charset="utf-8" />
<meta name="generator" content="Docutils 0.23: https://docutils.sourceforge.io/" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<style>body,footer,header{max-width:none!important;width:100%;padding:1px 2%;margin:0 auto;}</style><title>Operating Systems - Memory (By Ahmad Yoosofan)</title>
<link rel="stylesheet" href="./assets/style.css" type="text/css" />
<link rel="stylesheet" href="./assets/style.css" type="text/css" />
<style>body,footer,header{max-width:none!important;width:100%;padding:1px 2%;margin:0 auto;}</style><style>body.full .next:not(.active):not(.visited),body.full .incremental>*:not(.active):not(.visited),body.full .overlay>*:not(.active):not(.visited){visibility:hidden}body.full section.slide{padding-bottom:1rem;break-after:auto;background-color:#ffffff;}</style>
<script src="assets/b6plus.js"></script>
<style type="text/css">
/* Minimal style sheet for the HTML output of Docutils. */
/* */
/* :Author: Günter Milde, based on html4css1.css by David Goodger */
/* :Id: $Id: minimal.css 10018 2025-03-06 16:19:15Z milde $ */
/* :Copyright: © 2015, 2021 Günter Milde. */
/* :License: Released under the terms of the `2-Clause BSD license`_, */
/* in short: */
/* */
/* Copying and distribution of this file, with or without modification, */
/* are permitted in any medium without royalty provided the copyright */
/* notice and this notice are preserved. */
/* */
/* This file is offered as-is, without any warranty. */
/* */
/* .. _2-Clause BSD license: http://www.spdx.org/licenses/BSD-2-Clause */
/* This CSS3 stylesheet defines rules for Docutils elements without */
/* HTML equivalent. It is required to make the document semantics visible. */
/* */
/* .. _validates: http://jigsaw.w3.org/css-validator/validator$link */
/* titles */
p.topic-title,
p.admonition-title,
p.system-message-title {
font-weight: bold;
}
p.sidebar-title,
p.rubric {
font-weight: bold;
font-size: larger;
}
p.rubric {
color: maroon;
}
p.subtitle,
p.section-subtitle,
p.sidebar-subtitle {
font-weight: bold;
margin-top: -0.5em;
}
h1 + p.subtitle {
font-size: 1.6em;
}
a.toc-backref {
color: inherit;
text-decoration: none;
}
/* Warnings, Errors */
.system-messages h2,
.system-message-title,
pre.problematic,
span.problematic {
color: red;
}
/* Inline Literals */
.docutils.literal {
font-family: monospace;
white-space: pre-wrap;
}
/* do not wrap at hyphens and similar: */
.literal > span.pre { white-space: nowrap; }
/* keep line-breaks (\n) visible */
.pre-wrap { white-space: pre-wrap; }
/* Lists */
/* compact and simple lists: no margin between items */
.simple li, .simple ul, .simple ol, .simple > li p,
.compact li, .compact ul, .compact ol, .compact > li p,
dl.simple > dd, dl.compact > dd, dl.docinfo > dd {
margin-top: 0;
margin-bottom: 0;
}
/* Nested Paragraphs */
p:first-child { margin-top: 0; }
p:last-child { margin-bottom: 0; }
details > p:last-child { margin-bottom: 1em; }
/* Table of Contents */
.contents ul.auto-toc { /* section numbers present */
list-style-type: none;
}
/* Enumerated Lists */
ol.arabic { list-style: decimal }
ol.loweralpha { list-style: lower-alpha }
ol.upperalpha { list-style: upper-alpha }
ol.lowerroman { list-style: lower-roman }
ol.upperroman { list-style: upper-roman }
/* Definition Lists and Derivatives */
dt .classifier { font-style: italic }
dt .classifier:before {
font-style: normal;
margin: 0.5em;
content: ":";
}
/* Field Lists and similar */
/* bold field name, content starts on the same line */
dl.field-list,
dl.option-list,
dl.docinfo {
display: flow-root;
}
dl.field-list > dt,
dl.option-list > dt,
dl.docinfo > dt {
font-weight: bold;
clear: left;
float: left;
margin: 0;
padding: 0;
padding-right: 0.25em;
}
/* Offset for field content (corresponds to the --field-name-limit option) */
dl.field-list > dd,
dl.option-list > dd,
dl.docinfo > dd {
margin-left: 9em; /* ca. 14 chars in the test examples, fit all Docinfo fields */
}
/* start nested lists on new line */
dd > dl:first-child,
dd > ul:first-child,
dd > ol:first-child {
clear: left;
}
/* start field-body on a new line after long field names */
dl.field-list > dd > *:first-child,
dl.option-list > dd > *:first-child
{
display: inline-block;
width: 100%;
margin: 0;
}
/* Bibliographic Fields (docinfo) */
dl.docinfo pre.address {
font: inherit;
margin: 0;
}
dl.docinfo > dd.authors > p { margin: 0; }
/* Option Lists */
dl.option-list > dt { font-weight: normal; }
span.option { white-space: nowrap; }
/* Footnotes and Citations */
.footnote, .citation { margin: 1em 0; } /* default paragraph skip (Firefox) */
/* hanging indent */
.citation { padding-left: 2em; }
.footnote { padding-left: 1.7em; }
.footnote.superscript { padding-left: 1.0em; }
.citation > .label { margin-left: -2em; }
.footnote > .label { margin-left: -1.7em; }
.footnote.superscript > .label { margin-left: -1.0em; }
.footnote > .label + *,
.citation > .label + * {
display: inline-block;
margin-top: 0;
vertical-align: top;
}
.footnote > .backrefs + *,
.citation > .backrefs + * {
margin-top: 0;
}
.footnote > .label + p, .footnote > .backrefs + p,
.citation > .label + p, .citation > .backrefs + p {
display: inline;
vertical-align: inherit;
}
.backrefs { user-select: none; }
.backrefs > a { font-style: italic; }
/* superscript footnotes */
a[role="doc-noteref"].superscript,
.footnote.superscript > .label,
.footnote.superscript > .backrefs {
vertical-align: super;
font-size: smaller;
line-height: 1;
}
a[role="doc-noteref"].superscript > .fn-bracket,
.footnote.superscript > .label > .fn-bracket {
/* hide brackets in display but leave for copy/paste */
display: inline-block;
width: 0;
overflow: hidden;
}
[role="doc-noteref"].superscript + [role="doc-noteref"].superscript {
padding-left: 0.15em; /* separate consecutive footnote references */
/* TODO: unfortunately, "+" also selects with text between the references. */
}
/* Alignment */
.align-left {
text-align: left;
margin-right: auto;
}
.align-center {
text-align: center;
margin-left: auto;
margin-right: auto;
}
.align-right {
text-align: right;
margin-left: auto;
}
.align-top { vertical-align: top; }
.align-middle { vertical-align: middle; }
.align-bottom { vertical-align: bottom; }
/* reset inner alignment in figures and tables */
figure.align-left, figure.align-right,
table.align-left, table.align-center, table.align-right {
text-align: inherit;
}
/* Text Blocks */
.topic { margin: 1em 2em; }
.sidebar,
.admonition,
.system-message {
margin: 1em 2em;
border: thin solid;
padding: 0.5em 1em;
}
div.line-block { display: block; }
div.line-block div.line-block, pre { margin-left: 2em; }
/* Code line numbers: don't copy with drag-and-drop */
pre.code .ln { display: none; }
pre.code code:before {
content: attr(data-lineno);
font-size: small;
color: gray;
}
/* Tables */
table {
border-collapse: collapse;
}
td, th {
border: thin solid silver;
padding: 0 1ex;
}
.borderless td, .borderless th {
border: 0;
padding: 0;
padding-right: 0.5em /* separate table cells */
}
table > caption, figcaption {
text-align: left;
margin-top: 0.2em;
margin-bottom: 0.2em;
}
table.captionbelow {
caption-side: bottom;
}
/* MathML (see "math.css" for --math-output=HTML) */
math .boldsymbol { font-weight: bold; }
math.boxed, math .boxed {padding: 0.25em; border: thin solid; }
/* style table similar to AMS "align" or "aligned" environment: */
mtable.cases > mtr > mtd { text-align: left; }
mtable.ams-align > mtr > mtd { padding-left: 0; padding-right: 0; }
mtable.ams-align > mtr > mtd:nth-child(2n) { text-align: left; }
mtable.ams-align > mtr > mtd:nth-child(2n+1) { text-align: right; }
mtable.ams-align > mtr > mtd:nth-child(2n+3) { padding-left: 2em; }
.mathscr mi, mi.mathscr {
font-family: STIX, XITSMathJax_Script, rsfs10,
"Asana Math", Garamond, cursive;
}
/* Document Header and Footer */
header { border-bottom: 1px solid black; }
footer { border-top: 1px solid black; }
/* Images are block-level by default in Docutils */
/* New HTML5 block elements: set display for older browsers */
img, svg, header, footer, main, aside, nav, section, figure, video, details {
display: block;
}
svg { width: auto; height: auto; } /* enable scaling of SVG images */
/* inline images */
p img, p svg, p video,
h1 img, h2 img, h3 img, h4 img, h5 img, h6 img,
h1 svg, h2 svg, h3 svg, h4 svg, h5 svg, h6 svg {
display: inline;
}
</style>
<style type="text/css">
/* CSS31_ style sheet for the output of Docutils HTML writers. */
/* Rules for easy reading and pre-defined style variants. */
/* */
/* :Author: Günter Milde, based on html4css1.css by David Goodger */
/* :Id: $Id: plain.css 10079 2025-04-10 12:01:48Z milde $ */
/* :Copyright: © 2015 Günter Milde. */
/* :License: Released under the terms of the `2-Clause BSD license`_, */
/* in short: */
/* */
/* Copying and distribution of this file, with or without modification, */
/* are permitted in any medium without royalty provided the copyright */
/* notice and this notice are preserved. */
/* */
/* This file is offered as-is, without any warranty. */
/* */
/* .. _2-Clause BSD license: http://www.spdx.org/licenses/BSD-2-Clause */
/* .. _CSS3: https://www.w3.org/Style/CSS/ */
/* Document Structure */
/* ****************** */
/* "page layout" */
body {
margin: 0;
background-color: #dbdbdb;
--field-indent: 9em; /* default indent of fields in field lists */
}
main, footer, header {
line-height:1.6;
/* avoid long lines --> better reading */
/* optimum is 45…75 characters/line <http://webtypography.net/2.1.2> */
/* OTOH: lines should not be too short because of missing hyphenation, */
max-width: 50rem;
padding: 1px 2%; /* 1px on top avoids grey bar above title (mozilla) */
margin: auto;
}
main {
counter-reset: table figure;
background-color: white;
}
footer, header {
font-size: smaller;
padding: 0.5em 2%;
border: none;
}
/* Table of Contents */
ul.auto-toc > li > p {
padding-left: 1em;
text-indent: -1em;
}
nav.contents ul {
padding-left: 1em;
}
main > nav.contents ul ul ul ul:not(.auto-toc) {
list-style-type: '\2B29\ ';
}
main > nav.contents ul ul ul ul ul:not(.auto-toc) {
list-style-type: '\2B1D\ ';
}
/* Transitions */
hr.docutils {
width: 80%;
margin-top: 1em;
margin-bottom: 1em;
clear: both;
}
/* Paragraphs */
/* vertical space (parskip) */
p, ol, ul, dl, li,
.footnote, .citation,
div > math,
table {
margin-top: 0.5em;
margin-bottom: 0.5em;
}
h1, h2, h3, h4, h5, h6,
dd, details > p:last-child {
margin-bottom: 0.5em;
}
/* Lists */
/* ===== */
/* Definition Lists */
/* Indent lists nested in definition lists */
dd > ul:only-child, dd > ol:only-child { padding-left: 1em; }
/* Description Lists */
/* styled like in most dictionaries, encyclopedias etc. */
dl.description {
display: flow-root;
}
dl.description > dt {
font-weight: bold;
clear: left;
float: left;
margin: 0;
padding: 0;
padding-right: 0.3em;
}
dl.description > dd:after {
display: table;
content: "";
clear: left; /* clearfix for empty descriptions */
}
/* Field Lists */
dl.field-list > dd,
dl.docinfo > dd {
margin-left: var(--field-indent); /* adapted in media queries or HTML */
}
/* example for custom field-name width */
dl.field-list.narrow > dd {
--field-indent: 5em;
}
/* run-in: start field-body on same line after long field names */
dl.field-list.run-in > dd p {
display: block;
}
/* Bibliographic Fields */
/* generally, bibliographic fields use dl.docinfo */
/* but dedication and abstract are placed into divs */
div.abstract p.topic-title {
text-align: center;
}
div.dedication {
margin: 2em 5em;
text-align: center;
font-style: italic;
}
div.dedication p.topic-title {
font-style: normal;
}
/* disclosures */
details { padding-left: 1em; }
summary { margin-left: -1em; }
/* Text Blocks */
/* =========== */
/* Literal Blocks */
pre.literal-block, pre.doctest-block,
pre.math, pre.code {
font-family: monospace;
}
/* Block Quotes and Topics */
bockquote { margin: 1em 2em; }
blockquote p.attribution {
text-align: right;
margin-left: 20%;
}
/* Tables */
/* ====== */
/* th { vertical-align: bottom; } */
table tr { text-align: left; }
/* "booktabs" style (no vertical lines) */
table.booktabs {
border: 0;
border-top: 2px solid;
border-bottom: 2px solid;
border-collapse: collapse;
}
table.booktabs * {
border: 0;
}
table.booktabs th {
border-bottom: thin solid;
}
/* numbered tables (counter defined in div.document) */
table.numbered > caption:before {
counter-increment: table;
content: "Table " counter(table) ": ";
font-weight: bold;
}
/* Explicit Markup Blocks */
/* ====================== */
/* Footnotes and Citations */
/* ----------------------- */
/* line on the left */
.footnote-list {
border-left: solid thin;
padding-left: 0.25em;
}
/* Directives */
/* ---------- */
/* Body Elements */
/* ~~~~~~~~~~~~~ */
/* Images and Figures */
/* let content flow to the side of aligned images and figures */
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<section class="slide">
<h2>Operating Systems</h2>
<p><strong>Memory Management</strong></p>
<p>Ahmad Yoosofan</p>
<p><a class="reference external" href="https://yoosofan.github.io/">https://yoosofan.github.io/</a></p>
<p><a class="reference external" href="https://yoosofan.github.io/slide/os.mem.presentation.html">https://yoosofan.github.io/slide/os.mem.presentation.html</a></p>
<p><a class="reference external" href="https://yoosofan.github.io/slide/os.mem.rst">https://yoosofan.github.io/slide/os.mem.rst</a></p>
<p><a class="reference external" href="https://yoosofan.github.io/course/os.html">https://yoosofan.github.io/course/os.html</a></p>
<div class="slide-number">1</div></section>
<section class="slide t2c">
<h2>Fixed Partitioining or Static Partitioning</h2>
<img alt="os/img/memory/memory_fixed_partitioning.png" class="align-center" src="os/img/memory/memory_fixed_partitioning.png" style="height: 600px;" />
<ul class="incremental">
<li><p>Equal-Size Partitions</p></li>
<li><p>Unequal-Size Partitions</p></li>
<li><dl class="simple">
<dt>Pros:</dt>
<dd><ul class="simple">
<li><p>Minimal Hardware Complexity</p></li>
<li><p>Simple OS Logic</p></li>
<li><p>Low Overhead</p></li>
</ul>
</dd>
</dl>
</li>
<li><dl class="simple">
<dt>Cons:</dt>
<dd><ul class="simple">
<li><p>Internal Fragmentation</p></li>
<li><p>Fixed Process Limit</p></li>
<li><p>Maximum Size Limit</p></li>
</ul>
</dd>
</dl>
</li>
<li><img alt="os/img/memory/memory_fixed_partitioning_internal_fragmentation.png" class="align-center" src="os/img/memory/memory_fixed_partitioning_internal_fragmentation.png" style="width: 300px;" />
</li>
</ul>
<!-- :
operating system internal memory fragmentation fixed size partitioning
Multi Programming
https://www.geeksforgeeks.org/difference-between-internal-and-external-fragmentation/
مشکلات بخشبندی ثابت
.. class:: rtl
#. انعطاف بسیار پایین
#. محدودیت زیاد برای اندازهٔ فرایند در حالی که فضای حافظه خالی است.
#. تکه تکه شدن یا پراکندی داخلی internal fragmentation
#. هدر رفت حافظه
* بخشی از حافظه که به فرایند داده شده است فقط برای آن فرایند است.
* یعنی اگر بخشی از آن را فرایند به کار نبرد هدر رفته است.
- - - -
.. class:: rtl-h1
تخصیص حافظه به فرآیندها در حالت بخشبندی ثابت حافظه
.. image:: os/img/memory/memory_fixed_allocation.png
:align: center
- - - -
.. class:: rtl-h1
بخشبندی پویای حافظه
.. image:: os/img/memory/memory_management_pc.png
:align: center
:height: 470px -->
<div class="slide-number">2</div></section>
<section class="slide t2c">
<h2>Dynamic Partitioning</h2>
<img alt="os/img/memory/memory_effect_of_dynamic_partitioning.png" class="align-center" src="os/img/memory/memory_effect_of_dynamic_partitioning.png" />
<ul class="incremental">
<li><dl class="simple">
<dt>Hole Tracking or free space tracking</dt>
<dd><ul class="simple">
<li><p>Bitmaps</p></li>
<li><p>Linked Lists</p></li>
</ul>
</dd>
</dl>
</li>
<li><p>External fragmentation</p></li>
<li><table class="incremental">
<tbody>
<tr><td><p>Feature</p></td>
<td><p>Fixed</p></td>
<td><p>Dynamic</p></td>
</tr>
<tr><td><p>Partition Size</p></td>
<td><p>Static</p></td>
<td><p>Dynamic</p></td>
</tr>
<tr><td><p>Fragmentation</p></td>
<td><p>Internal</p></td>
<td><p>External</p></td>
</tr>
<tr><td><p>Efficiency</p></td>
<td><p>Low</p></td>
<td><p>High</p></td>
</tr>
</tbody>
</table>
</li>
<li><dl class="simple">
<dt>Coalescing (The "Neighborly" Cleanup)</dt>
<dd><ul class="simple">
<li><p>Merge free space</p></li>
</ul>
</dd>
</dl>
</li>
<li><p>compaction</p></li>
</ul>
<!-- csv-table:
:class: step
Feature,Fixed Partitioning,Dynamic Partitioning
Partition Size,Static (set at boot),Dynamic (set at load-time)
Fragmentation,Internal (Space wasted inside),External (Space wasted between)
Compaction,Not needed,Essential
Efficiency,Low (Wasteful of RAM),High (Better RAM utilization) -->
<!-- :
Thanks Gemini AI for the above table -->
<div class="slide-number">3</div></section>
<section class="slide t2c">
<h2>Placement algorithms</h2>
<img alt="os/img/memory/memory_select_part_for_allocation.png" class="align-center" src="os/img/memory/memory_select_part_for_allocation.png" />
<ul class="incremental simple">
<li><dl class="simple">
<dt>First Fit</dt>
<dd><ul>
<li><p>pros: fast</p></li>
<li><p>cons: clog</p></li>
</ul>
</dd>
</dl>
</li>
<li><dl class="simple">
<dt>Best Fit</dt>
<dd><ul>
<li><p>pros:</p></li>
<li><p>cons: Slow, Small holes</p></li>
</ul>
</dd>
</dl>
</li>
<li><dl class="simple">
<dt>Worst Fit</dt>
<dd><ul>
<li><p>pros: large leftover</p></li>
<li><p>cons: slow, use largest</p></li>
</ul>
</dd>
</dl>
</li>
<li><dl class="simple">
<dt>Next Fit</dt>
<dd><ul>
<li><p>pros: Prevents clogging</p></li>
<li><p>cons:</p></li>
</ul>
</dd>
</dl>
</li>
<li><dl class="simple">
<dt>Quick Fit or Segregated Fit (different lists)</dt>
<dd><ul>
<li><p>pros: instant allocation</p></li>
<li><p>cons: overhead of OS</p></li>
</ul>
</dd>
</dl>
</li>
</ul>
<!-- :
Algorithm,Search Effort,Leftover Fragment,Primary Weakness
First Fit,Low (Partial Scan),Variable,Fragments the start of RAM
Next Fit,Low (Partial Scan),Variable,Fragments the end of RAM
Best Fit,High (Full Scan),Smallest,"Creates tiny, useless ""slivers"""
Worst Fit,High (Full Scan),Largest,Eliminates large contiguous blocks
5. Quick Fit (or Segregated Fit)
Commonly used in real-world modern kernels and memory allocators (like malloc).
The Strategy: The OS maintains separate linked lists for common requested sizes (e.g., a list for 4KB holes, a list for 16KB holes, etc.).
Pros: Near-instant allocation for standard sizes.
Cons: High overhead for the OS to maintain and "bin" these holes.- - - - -->
<div class="slide-number">4</div></section>
<section class="slide t2c">
<h2>Compaction or Defragmentation</h2>
<div class="graphviz-container" style="margin: 0 auto; text-align: center;">
<svg width="540pt" height="261pt"
viewBox="0.00 0.00 540.00 261.00" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<g id="graph0" class="graph" transform="scale(1 1) rotate(0) translate(4 257)">
<title>Compaction</title>
<polygon fill="white" stroke="transparent" points="-4,4 -4,-257 536,-257 536,4 -4,4"/>
<text text-anchor="middle" x="266" y="-237.8" font-family="Times,serif" font-size="14.00">Memory Compaction: Merging External Fragments</text>
<!-- Before -->
<g id="node1" class="node">
<title>Before</title>
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<text text-anchor="start" x="19.5" y="-203.8" font-family="Courier New" font-size="14.00">Process A (10KB)</text>
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<text text-anchor="start" x="36" y="-167.8" font-family="Courier New" font-weight="bold" font-size="14.00">Hole 1 (5KB)</text>
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<polygon fill="none" stroke="black" points="8.5,-115 8.5,-152 163.5,-152 163.5,-115 8.5,-115"/>
<text text-anchor="start" x="19.5" y="-129.8" font-family="Courier New" font-size="14.00">Process B (15KB)</text>
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<polygon fill="none" stroke="black" points="8.5,-78 8.5,-115 163.5,-115 163.5,-78 8.5,-78"/>
<text text-anchor="start" x="32" y="-93.8" font-family="Courier New" font-weight="bold" font-size="14.00">Hole 2 (10KB)</text>
<polygon fill="#d1d1d1" stroke="transparent" points="8.5,-41 8.5,-78 163.5,-78 163.5,-41 8.5,-41"/>
<polygon fill="none" stroke="black" points="8.5,-41 8.5,-78 163.5,-78 163.5,-41 8.5,-41"/>
<text text-anchor="start" x="19.5" y="-55.8" font-family="Courier New" font-size="14.00">Process C (10KB)</text>
<polygon fill="#ffffff" stroke="transparent" points="8.5,-4 8.5,-41 163.5,-41 163.5,-4 8.5,-4"/>
<polygon fill="none" stroke="black" points="8.5,-4 8.5,-41 163.5,-41 163.5,-4 8.5,-4"/>
<text text-anchor="start" x="32" y="-19.8" font-family="Courier New" font-weight="bold" font-size="14.00">Hole 3 (20KB)</text>
</g>
<!-- After -->
<g id="node2" class="node">
<title>After</title>
<polygon fill="#d1d1d1" stroke="transparent" points="312,-173 312,-210 524,-210 524,-173 312,-173"/>
<polygon fill="none" stroke="black" points="312,-173 312,-210 524,-210 524,-173 312,-173"/>
<text text-anchor="start" x="351.5" y="-187.8" font-family="Courier New" font-size="14.00">Process A (10KB)</text>
<polygon fill="#d1d1d1" stroke="transparent" points="312,-136 312,-173 524,-173 524,-136 312,-136"/>
<polygon fill="none" stroke="black" points="312,-136 312,-173 524,-173 524,-136 312,-136"/>
<text text-anchor="start" x="351.5" y="-150.8" font-family="Courier New" font-size="14.00">Process B (15KB)</text>
<polygon fill="#d1d1d1" stroke="transparent" points="312,-99 312,-136 524,-136 524,-99 312,-99"/>
<polygon fill="none" stroke="black" points="312,-99 312,-136 524,-136 524,-99 312,-99"/>
<text text-anchor="start" x="351.5" y="-113.8" font-family="Courier New" font-size="14.00">Process C (10KB)</text>
<polygon fill="#ffffff" stroke="transparent" points="312,-19 312,-99 524,-99 524,-19 312,-19"/>
<polygon fill="none" stroke="black" points="312,-19 312,-99 524,-99 524,-19 312,-19"/>
<text text-anchor="start" x="323" y="-56.3" font-family="Courier New" font-weight="bold" font-size="14.00">Total Free Space (35KB)</text>
</g>
<!-- Before->After -->
<g id="edge1" class="edge">
<title>Before->After</title>
<path fill="none" stroke="black" d="M171.18,-115C208.46,-115 252.99,-115 293.84,-115"/>
<polygon fill="black" stroke="black" points="293.86,-118.5 303.86,-115 293.86,-111.5 293.86,-118.5"/>
<text text-anchor="middle" x="237.5" y="-118.4" font-family="Times,serif" font-size="12.00" fill="red"> COMPACTION </text>
</g>
</g>
</svg>
</div>
<ul class="incremental simple">
<li><dl class="simple">
<dt>cost</dt>
<dd><ul>
<li><p>CPU Cycles</p></li>
<li><p>Bus Saturation</p></li>
<li><p>System Freeze</p></li>
</ul>
</dd>
</dl>
</li>
<li><dl class="simple">
<dt>Strategies</dt>
<dd><ul>
<li><p>Move to One End</p></li>
<li><p>Minimal Movement</p></li>
</ul>
</dd>
</dl>
</li>
<li><dl class="simple">
<dt>Trigger</dt>
<dd><ul>
<li><p>Allocation Failure</p></li>
<li><p>Idle Time</p></li>
<li><p>Threshold</p></li>
</ul>
</dd>
</dl>
</li>
<li><dl class="simple">
<dt>Pros</dt>
<dd><ul>
<li><p>Maximizes RAM Utilization</p></li>
<li><p>Enables Large Processes</p></li>
<li><p>Simplifies Placement</p></li>
</ul>
</dd>
</dl>
</li>
<li><dl class="simple">
<dt>Cons</dt>
<dd><ul>
<li><p>Extreme Overhead</p></li>
<li><p>Requires Special Hardware</p></li>
<li><p>Interrupts Execution</p></li>
</ul>
</dd>
</dl>
</li>
</ul>
<!-- :
.. image:: os/img/memory/compaction.svg
:align: center
Pros,Cons
Maximizes RAM Utilization: Prevents jobs from waiting when there is theoretically enough space.,Extreme Overhead: Copying megabytes or gigabytes of RAM is slow.
Enables Large Processes: Allows the system to accommodate programs that otherwise couldn't fit.,Requires Special HW: Needs an MMU/Base-Limit registers to work.
"Simplifies Placement: After compaction, ""First Fit"" becomes trivial because there is only one hole.","Interrupts Execution: Can cause ""stuttering"" in real-time or interactive systems."
https://web.fe.up.pt/~arestivo/presentation/os-memory/#15
Memory-Compaction-in-contiguous-memory-allocation-1.jpg
https://binaryterms.com/contiguous-memory-allocation-in-operating-system.html
compaction.png
https://github.com/mor1/ia-operating-systems/wiki/06-Virtual-Addressing
https://github.com/mor1/ia-operating-systems
https://www.faceprep.in/operating-systems/operating-systems-fragmentation-and-compaction/
https://slideplayer.com/slide/7084682/ -->
<div class="slide-number">5</div></section>
<section class="slide">
<h2>Buddy System Memory Management(I)</h2>
<img alt="os/img/memory/memory_buddy_system2.png" class="align-center" src="os/img/memory/memory_buddy_system2.png" />
<div class="slide-number">6</div></section>
<section class="slide t4c">
<h2>Buddy System Memory Management(II)</h2>
<div class="graphviz-container" style="margin: 0 auto; text-align: center;">
<svg width="220"
viewBox="0.00 0.00 224.50 283.00" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
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<text text-anchor="middle" x="108.25" y="-259.8" font-family="Times,serif" font-size="14.00">A 100</text>
<!-- 0 -->
<g id="node1" class="node">
<title>0</title>
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<text text-anchor="middle" x="148" y="-230.3" font-family="Times,serif" font-size="14.00">1 M</text>
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<text text-anchor="middle" x="110" y="-158.3" font-family="Times,serif" font-size="14.00">512 K</text>
</g>
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<g id="edge1" class="edge">
<title>0->1</title>
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