A Thin client is a computer which depends heavily on some other computer (typically a server) to get the required software loaded. All the commands issued from the thin client PC is actually executed on the server. Because of this even if you are using an old PC (i.e. 386 or 486) you will be able to get speed like a new Celeron or Core 2 Duo computer or even like a Xeon server.
Benefits of using a thin client:
A thin client is not a complete computer, that means it does not have any local storage which reduces capital expenses towards a desktop PC. Furthermore, the overhead costs associated with administration, maintenance, support, security and installation are also significantly lower than a traditional PC.
We can use old computers by implementing Thin Client technology. Your old PCs will work like new PC.