Analogy 01.

Grid Computing: We use electricity for home appliances without knowing how electric power is generated and distributed to our home.

Grid computing is exactly the same, here, electric power is processing power of computers and appliances are our problems to be solved using computers. So grid computing creates a single system image.

Grid computing is not distributed computing, which need physical proximity and operating homogeneity, grids can be geographically distributed and heterogeneous and grid computing keeps complexity hidden.

So Grid computing is virtualizes as one large computing system.

Analogy 02.

Single Computer (PC) -> Local area Network (LAN) -> Wide area network (WAN) -> Internet.

Single computer resource -> clustered computer resources -> Distributed Computer resources -> Grid computing resources.