If you bought a new computer recently, or if you are wading through advertising material because you plan to buy a computer soon, you will be familiar with terms such as "Dual Core" and "Quad Core." A whole new crop of consumer computers includes two- or even four-core CPUs, taking the humble PC into what used to be the domain of high-end servers and workstations. But just because you have a multi-processor system doesn't mean all the processors are working hard.

In reality, often only one processor is busy. Figure 1 shows the top program output for Xaos, a fractal calculation program. The program seems to be using 100 percent of the CPU. But appearances can be deceptive: The computer's actual load is just 60 percent.

Pressing the 1 button lists the CPUs separately. In this mode (Figure 2), you can easily see the load on the individual cores: One CPU is working hard (90 percent load), while the other is twiddling its thumbs (0.3 percent load).

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