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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">System image</span></span>

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<p>In <a href="Computing" title="Computing">computing</a>, a <b>system image</b> is a <a href="Serialization" title="Serialization">serialized</a> copy of the entire <a href="State_(computer_science)" title="State (computer science)">state</a> of a <a href="Computer_system" class="mw-redirect" title="Computer system">computer system</a> stored in some <a href="Computer_data_storage" title="Computer data storage">non-volatile</a> form, such as a binary executable <a href="Computer_file" title="Computer file">file</a>.

</p><p>If a system has all its state written to a disk (i.e. on a <a href="Disk_image" title="Disk image">disk image</a>), then a system image can be produced by copying the disk to a file elsewhere, often with <a href="Disk_cloning" title="Disk cloning">disk cloning</a> applications. On many systems a complete system image cannot be created by a disk cloning program running within that system because information can be held outside of disks and volatile memory, for example in non-volatile memory, such as <a href="Boot_ROM" title="Boot ROM">boot ROMs</a>.

</p><p>A system is said to be capable of using system images if it can be shut down and later restored to exactly the same state. In such cases, system images can be used for <a href="Backup" title="Backup">backup</a>.

</p><p><a href="Hibernation_(computing)" title="Hibernation (computing)">Hibernation</a> is an example that uses an image of the computer's entire <a href="Random-access_memory" title="Random-access memory">RAM</a>.

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<div class="mw-heading mw-heading2"><h2 id="Process_images">Process images</h2></div>

<p>A <a href="Process_(computing)" title="Process (computing)">process</a> image is a copy of a given process's <a href="State_(computer_science)" title="State (computer science)">state</a> at a given point in time. It is often used to create <a href="Persistence_(computer_science)" title="Persistence (computer science)">persistence</a> within an otherwise volatile system. A common example is a <a href="Database_management_system" class="mw-redirect" title="Database management system">database management system</a> (DBMS). Most DBMS can store the state of its <a href="Database" title="Database">database</a> or databases to a file before being closed down (see <a href="Database_dump" title="Database dump">database dump</a>). The DBMS can then be restarted later with the information in the database intact and proceed as though the software had never stopped. Another example would be the <a href="Hibernate_(OS_feature)" class="mw-redirect" title="Hibernate (OS feature)">hibernate</a> feature of many operating systems. Here, the state of all <a href="Random-access_memory" title="Random-access memory">RAM</a> memory is stored to disk, the computer is brought into an energy saving mode, then later restored to normal operation.

</p><p>Some <a href="Emulator" title="Emulator">emulators</a> provide a facility to save an image of the system being emulated. In video gaming this is often referred to as a <a href="Savestate" class="mw-redirect" title="Savestate">savestate</a>.

</p><p>Another use is <a href="Code_mobility" title="Code mobility">code mobility</a>: a <a href="Mobile_agent" title="Mobile agent">mobile agent</a> can migrate between machines by having its state saved, then copying the data to another machine and restarting there.

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<div class="mw-heading mw-heading3"><h3 id="Programming_language_support">Programming language support</h3></div>

<p>Some <a href="Programming_language" title="Programming language">programming languages</a> provide a command to take a system image of a program. This is normally a standard feature in <a href="Smalltalk" title="Smalltalk">Smalltalk</a> (inspired by <a rel="nofollow" class="external text" href="http://www.mprove.de/diplom/gui/kay68.html">FLEX</a>) and <a href="Lisp_(programming_language)" title="Lisp (programming language)">Lisp</a>, among other languages. Development in these languages is often quite different from many other programming languages. For example, in Lisp the programmer may load packages or other code into a running Lisp <a href="Implementation" title="Implementation">implementation</a> using the <a href="Read-eval-print_loop" class="mw-redirect" title="Read-eval-print loop">read-eval-print loop</a>, which usually compiles the programs. Data is loaded into the running Lisp system. The programmer may then <a href="ROM_image" title="ROM image">dump</a> a system image, containing that pre-compiled and possibly customized code—and also all loaded application data.

Often this image is an executable, and can be run on other machines. This system image can be the form in which executable programs are distributed—this method has often been used by programs (such as <a href="TeX" title="TeX">TeX</a> and <a href="Emacs" title="Emacs">Emacs</a>) largely implemented in Lisp, Smalltalk, or <a href="Idiosyncratic" class="mw-redirect" title="Idiosyncratic">idiosyncratic</a> languages to avoid spending time repeating the same initialization work every time they start up.

</p><p>Similar, <a href="Lisp_Machine" class="mw-redirect" title="Lisp Machine">Lisp Machines</a> were booted from Lisp images, called Worlds. The World contains the complete operating system, its applications and its data in a single file. It was also possible to save incremental Worlds, that contain only the changes from some base World. Before saving the World, the Lisp Machine operating system could optimize the contents of memory (better memory layout, compacting data structures, sorting data, ...).

</p><p>Although its purpose is different, a "system image" is often similar in structure to a <a href="Core_dump" title="Core dump">core dump</a>.

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<ul><li><a href="ISO_image" class="mw-redirect" title="ISO image">ISO image</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://cryopid.berlios.de/">CryoPID</a> — A Process Freezer for <a href="Linux" title="Linux">Linux</a></li></ul></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2025-07-11" href="https://en.wikipedia.org/wiki/?title=System_image&oldid=1299946510">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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