The notion of a single-function server appliance is not new. Vendors such as Cisco have developed profitable businesses by selling kit such as network routers – the classic single-function server appliance. And such vendors offer an important lesson – that appliances become popular when they are based on accepted standards.

Specialised appliances such as Conformative’s XML accelerators and Neteeza’s database accelerators are increasingly common. Security appliances are also taking off, provided by vendors such as Network Engines, which aims at the Microsoft marketplace; and nCipher, which targets document security and uses Adobe’s LiveCycle Security Server.

An interesting extension of the appliance concept is to create packaged “appliance-like” functionality in software – an example of this would be the 40 or so pre-configured virtual machines available for free download from VMware. These include several open-source firewalls, commercial database evaluation systems and even a voice over IP (VoIP) server.