People who are new to the computer scene of today might think it is obvious that Intel has gone for high frequencies while AMD has been putting in more performance per clock cycle, with the different sacrifices these methods come with. It hasn't always been like this, actually far from it, and to get a better understanding of how the companies reasoned when they created the different architectures, we will do a quick historical flashback.

From P6 to NetBurst
About six years ago, in the beginning of the year 2000, information about Intel's successor for the PIII processor, the P4, started to surface. The PIII processor operated at about 800 MHz at the time, and was based on Intel's P6 architecture that had made its entrance at 150 MHz. The engineers at both AMD and Intel worked frantically to refine the manufacturing process to be able to increase the clock frequencies. The clock frequency was of the utmost importance, which at that time gave a very precise indication of the processor's performance, comparable to the competitor. In marketing, 1 GHz was a clear milestone and the hysteria increased more and more when both of the manufacturers launched products closer and closer to the 1 GHz level. AMD was declared victorious, which we assume Intel wasn't very happy about. Intel was working on its new architecture, dubbed NetBurst, which would greatly increase clock frequencies.

NetBurst
With NetBurst, Intel had taken the frequency initiative very seriously, which was the thing that was focused upon when the core was constructed. To make this increase in frequency possible, some areas had to be compromised, such as the length of the so called pipeline. To explain it in layman's terms, the pipeline can be thought of as a queue. Every step in this queue prepares data and instructions for a final execution. The P6 architecture used a pipeline that consisted of 10 steps, which Intel increased by the double for NetBurst at its launch. Thanks to refined manufacturing processes, the manufacturer had succeeded in increasing the frequency of a P6 processor from 150 MHz to 1 GHz (and later on, 1.4 GHz with the Tualatin core). With this in mind and with the changes that had been made for NetBurst, Intel simply aimed for increasing the frequency tenfold, to 10 GHz. NetBurst started its era at 1,4 GHz and was made under the code name Willamette. In spite of the increased clock frequency, the performance was at its best equivalent to the PIII processor operating at 1 GHz, but in several cases slower because of the longer pipeline.

The successor, Northwood, increased the pipeline by one step, totaling at 21 steps. Thanks to a finer manufacturing process (130nm), it could be introduced at 1.6 GHz and finally scaled to 3.4 GHz. Everything seemed to be fine, and the architecture was starting to get pretty fast. At the time, Intel though that there were only a few refinements to be made to the manufacturing process until it would reach those really high frequencies. This proved to be easier said than done, and the problems were surfacing already at the 90nm manufacturing process. With the Prescott core, Intel hit some serious physical issues in the shape of increased leakage. This leakage made the processor substantially warmer than its predecessor at the same clock frequency, which was an effect the direct opposite of what had been experienced at previous process refinements. The NetBurst era had started to fall apart, and the expected Tejas core that would take over at 4 GHz was simply scrapped.

From NetBurst and back to P6
While the development team for NetBurst was working frantically with getting control of the new manufacturing process, another team within Intel received the mission to create a mobile processor with one requirement: extremely low power consumption. Some minor adjustments and optimizations were made to save energy, increase the performance and raise the frequencies. The code-name of this Pentium M processor, Banias, is far from well known. Its successor that was improved upon further is known better, not at least among enthusiasts, as Dothan. With the NetBurst architecture impoverished and constantly inferior to competing products, it was now time to create a new architecture, which would at most get minimal functions from NetBurst. It was simply time to learn from the development of the mobile processors and change alignment and the basic idea about the processors. Thus, Intel's next-generation microarchitecture was born, officially dubbed Core.

Before we go deeper with the details of the architecture, we'll take a look at the products being released by Intel based on the Core architecture.