Resource sharing is the crux of grid philosophy - but grid computing is not about getting something for nothing.

Grid computing is about putting mechanisms in place so that everyone involved benefits from the efficiencies and advantages of sharing.

Grids give you access to extra computing power: you can compute things using a grid that you cannot compute using just one computer or one computer centre. A grid can give you direct access to remote software, computers and data. It can even give you access and control of remote sensors, telescopes and other devices that do not belong to you.

Grid resources are owned by many different people who run different software, exist within different administrative domains, and use different systems for security and access. This presents a major challenge

Would you trust your car to a complete stranger? A computing grid is a bit like a car pool - sometimes you share your car with other people; other times, they share their car with you. These people could be strangers, but if they are part of the same car pool organization as you, you will generally trust each other at some level. If one guy is always late, the others will complain and eventually kick him out of the car pool. So there is trust, and there are mechanisms to deal with breach of trust.

For example, when the persons in charge of a computer centre decide to share their resources on a grid, they will normally put conditions on the use of those resources, specifying limits on which resources can be used when, and what can be done with them.