Typically a virtual appliance will have a web interface to configure the inner workings of the appliance. A virtual appliance is usually built to host a single application, and so represents a new way of deploying network applications.
As an example, the MediaWiki software that powers Wikipedia is available as a virtual appliance (wiki.rpath.com/wiki/Appliance:MediaWiki_Appliance). This appliance contains all the necessary software, including operating system, database and MediaWiki, to run a wiki installation as a "black box". en.wikipedia.org/wiki/Virtual_appliance
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A virtual appliance is a minimalist virtual machine (en.wikipedia.org/wiki/Virtual_machine) image designed to run under Parallels (en.wikipedia.org/wiki/Parallels%2C_Inc.), VMware (en.wikipedia.org/wiki/VMware), Xen (en.wikipedia.org/wiki/Xen), Microsoft Virtual PC (en.wikipedia.org/wiki/Microsoft_Virtual_PC), QEMU (en.wikipedia.org/wiki/QEMU), Usermode Linux (en.wikipedia.org/wiki/Usermode_Linux), CoLinux (en.wikipedia.org/wiki/CoLinux), Virtual Iron (en.wikipedia.org/wiki/Virtual_Iron), VirtualBox (en.wikipedia.org/wiki/VirtualBox) or other virtualization technology.
Virtual appliances are a subset of the broader class of software appliances (en.wikipedia.org/wiki/Software_Appliance). Like software appliances, virtual appliances are aimed to eliminate the installation, configuration and maintenance costs associated with running complex stacks of software.
A key concept that differentiates a virtual appliance from a virtual machine is that a virtual appliance is a fully pre-installed and pre-configured application and operating system environment whereas a virtual machine is, by itself, without application software.
Typically a virtual appliance will have a web interface to configure the inner workings of the appliance. A virtual appliance is usually built to host a single application, and so represents a new way of deploying network applications.
As an example, the MediaWiki software that powers Wikipedia is available as a virtual appliance (wiki.rpath.com/wiki/Appliance:MediaWiki_Appliance). This appliance contains all the necessary software, including operating system, database and MediaWiki, to run a wiki installation as a "black box".
en.wikipedia.org/wiki/Virtual_appliance