"So, why all the fuss over small, single-purpose virtual machines? Haven’t we been using these for years? Yes, in fact, we have been using them for years but the difference is that now there are commercial vendors who supply them, support them, and update them as they would any application or proprietary physical appliance. Virtual appliances make the vendor’s job easier in that they no longer have to support several different versions of physical systems in client data centers since virtual machines are hardware and platform independent. Keeping up with BIOS updates, firmware versions, and physical device age (product life cycle), and support issues for hundreds or thousands of client units is painful and costly. Vendor-supplied virtual appliance images available via download are ready-to-deploy and use.
"Linux-based appliances have other advantages as well. The operating system is free, most of the applications are free, and it’s easy to maintain locally or remotely. Of its advantages, perhaps the most compelling of all is its customizability including the ability to install a fully functional Linux system within a very small (~500MB) footprint using a system known as JeOS (Just Enough OS)– pronounced “juice.” Most virtual appliance vendors begin with a JeOS system as a base system for a virtual appliance."
