Different instruction sets perform work in different ways. Both philosophies were geared towards bringing new levels of performance to the user. Now HP and Intel have unified their considerable design knowledge to bring you the Itanium processor family architecture, which will set new standards for performance. The Itanium processor family architecture is the architectural specification that the processor family has in common. The key to the Itanium processor family architecture is the ability to carry out many different tasks at once and that is essentially what parallelism is.
Sequential events happen one after another, parallel events happen simultaneously.
If a construction firm is building a skyscraper, lots of events happen on site at the same time to ensure that the building is built as fast as possible. If the foundations are being laid at the same time as the concrete is being mixed and the scaffolding erected, it takes less time than it does if the concrete mixing and the scaffolding have to wait for foundation work to finish before they can be started. Modern processor architectures work on the same principle - they can do more than one operation at once. See implicit parallelism and explicit parallelism. Instead of waiting for each section of a complex calculation to finish, it is faster if the processor can predict the outcome and proceed on the basis of that prediction.