OVERVIEW

The faster you make a computer run, the harder it is to envision how to make it run still faster. It is no longer sufficient to just make the architecture process instructions faster. You must make more things happen at once that is, in parallel. The computer is not running faster it is simply getting more done at once.

The Itanium architecture employs a new parallel computer architecture called explicitly parallel instruction computing (EPIC). Intel Corporation s first hardware implementation of this architecture is the Itanium processor. EPIC offers many new features to increase performance, but the most important are explicit instruction level parallelism (ILP), speculation, predication, and a large register file. Each of these makes a computer run faster.

But what do you do with all this parallelism? The traditional problem is that we never have enough work ready to keep a machine fully busy. If we have all this power, the key is to not throw it away by letting it go unused. Anytime the processor is ready to do six more things, we don t want to give it two things to do and waste 66% of the processing power.

A breakthrough happens when you decide to stop worrying about only doing things we must. The approach is to ask the machine speculatively to do four more things. That is, things are picked that might be needed in the future, but right now we just aren t sure which of the four it will be. Let us say that the...