Inside the Machine

The Integer Execution Units

Though the Pentium 4’s double-pumped integer execution units got quite a bit of press when Netburst was first announced, you might be surprised to learn that both the G4e and the Pentium 4 embody approaches to enhancing integer performance that are very similar. As you’ll see, this similarity arises from both processors’ application of the computing design dictum: Make the common case fast.

For integer applications, the common case is easy to spot. As I outlined in Chapter 1, integer instructions generally fall into one of two categories:

Simple/fast integer instructions

Instructions like add and sub require very few steps to complete and are therefore easy to implement with little overhead. These simple instructions make ...