Big brains or fast feet? Those are the two broad choices for CPU architects. Some processors achieve high performance by using extra-complex logic. Others use simpler logic to race through calculations at faster clock speeds. Either approach works, but sometimes technology dictates which method is better at a point in time.
This time, Intel is betting on the “big brains” approach. Intel’s new microarchitecture, named Core, is the foundation for new x86 processors coming in mid-2006 and beyond. Don’t confuse it with today’s Core Duo processors, which use the older Banias (Pentium M) microarchitecture. Although the Core microarchitecture is based on Banias, it’s a fresh design not found in existing chips.
Core follows the “brainiac” philosophy. Brainiacs are complex processors that run at slower clock frequencies but perform more math than other speed-demon processors. Intel’s previous NetBurst microarchitecture was a speed demon. Its 31-stage instruction pipeline was the deepest ever seen in a general-purpose processor. Deeper pipelines enable higher clock speeds, but NetBurst sprinted into the brick wall of power dissipation.
By contrast, Core has a 14-stage pipeline. That’s still pretty deep, so Core processors won’t be slugs. And Intel has compensated by adding more pipelines, widening some datapaths, and making other improvements. NetBurst was a three-way superscalar design, whereas Core is a four-way machine. Core has 128-bit wide datapaths for floating-point and multimedia instructions, whereas NetBurst had 64-bit-wide datapaths. Core’s additional complexity delivers higher performance at lower clock frequencies.
Core’s four-way superscalar design is a little surprising. Executing four program instructions per clock cycle is a relatively rare event. Most superscalar processors struggle to average more than 1.5 instructions per cycle. However, the wider floating-point and multimedia datapaths should measurably improve gaming performance, which is critically important for home PCs. Intel has also dropped Hyper-Threading for now, but it will probably resurface in a future processor.
Overall, the Core microarchitecture makes intelligent trade-offs and paves the way for Intel to build multicore processors with two, four, or even eight cores in the near future. It also pressures AMD to do something marvelous with its own revised microarchitecture, expected this summer.