What is g in Oracle's grid computing?

Oracle defines Grid Computing like this -

With grid computing, groups of independent, modular hardware and software components can be connected and rejoined on demand to meet the changing needs of businesses.

What does it exactly mean?

We already know what is parallel computing. A complex task is dividided into smaller parts and each part is processed independently by a computer. Then the outputs are combined to get final result.

How does grid computing differ from this parallel computing?

Grid computing is an abstract (or virtualization, as Oracle says) concept. A grid can be an infrastructure grid, an appllication grid, an information grid and so on.

What - getting more confused? Ok, please read on.

In early days (~ 1980s) of database, the relational database management was starting to gain populartity. In RDBMS terms, a customer buys products and a transaction is generated. All these info like customer, product, transaction etc. are stored in RDBMS. They are linked together (by foreign keys, in 3rd normal form). So from a high level view, customer, product, transaction are all part of RDBMS.

Now come to the present days. We are gathering data like never before! Besides RDBMS, we now have lots of different stuffs like OLAP (Business Intelligence/Data Warehouse etc.), OLTP (transactional data), BPEL (Business Process Execution Language), Web services (using XML), OWB (Oracle Warehouse Builder) etc.

The grid is collection of all these - i.e. different applications and data which speak with one another.

Oracle has product of almost everything nowadays - which is wrapped around a buzzy name called Fusion Middleware. These components are designed so that one component (say OWB ) can interact with another (say core Oracle database). This constitute an architectural grid.

The relational data on your RDBMS can be termed as information grid.

There's another aspect of grid. Take Oracle Real Application Cluster or RAC. Here multiple instances of database are inter-connected to safeguard single point of failure. This is an example of infrastructure grid. Everything is part of grid. It is a concept. It could have been told as Matrix computing too. (Did you enjoy Matrix series of movies?)

Now you know what the buzzword Grid computing mean!