As mentioned in the previous chapter, Linux can be run on non-PC architectures. This is particularly useful for the small applications old PCs can be used for. Recent netbooks either ARM-based or MIPS-based provide an even smaller power footprint. Check moblin Linux, which is dedicated to such machines.
Linux is increasingly used in Consumer Electronics (CE) devices, in particular in network appliances such as Wifi routers, DSL modems, Network Attached Storage (NAS) servers, IP cameras and other small devices.
Thanks to the GNU GPL license, kernel and application source code for these devices are freely available. More and more device owners are taking advantage of this to develop other uses for these devices. Thanks to the progress of Linux in embedded systems, making its own embedded system is increasingly easy.
Using such devices instead of regular PCs yields many advantages: much lower power consumption, no noise (no fans), built with much fewer materials (small size), and much lower cost (for your purse and for the environment).
In a nutshell, do not buy a new PC for small applications. Reuse your old computers or buy a consumer device on which you can run Linux!