By now, many people have memorized Moore's Law: The number of transistors on CPUs doubles about every 18 months. Intel chairman Gordon Moore's law has been accurate for decades, for CPU evolution. What about total system performance, though? PC Magazine Labs recently decided to see whether Moore's Law also means that systems run twice as fast every year and a half. Joel Santo Domingo, project leader for our PCs and Devices team, headed up the testing effort.

"Moore was originally observing that the number of transistors on a chip doubles every 18 to 24 months," Santo Domingo says. "But people believe the law implies that performance doubles every 18 months. Moore's Law is very, very misquoted."

So Santo Domingo and his team tested the assumption. The team made use of a brand-new Gateway system with a 1.5-GHz Pentium 4 CPU. This system was compared with a four-year-old NEC machine with a 300-MHz Pentium II CPU.

The Pentium II CPU was released in May 1997 and had 7.5 million transistors. Three years and six months later, in November 2000, the Pentium 4 was released. For this 42-month period, Moore's Law declares that the number of CPU transistors should jump to about 40 million. In fact, the new Pentium 4 chip we tested had 42 million—slightly above the Moore's Law prediction.

Did total system performance jump by the same amount over that period? To find out, the team ran the Ziff Davis Business Winstone 2001 benchmark test program. Both the old and the new system had 128MB of RAM and ran Windows 2000 SP1. The results were enlightening. The old system scored 13.9. The new system's score of 43.5 represented a significant increase in speed—but was well short of the 74.1 score that would result from a doubling of total system performance every 18 months.

If CPU speeds and transistor counts are still doubling at a fast clip, what's holding us back? Neither memory speeds nor bus speeds are growing at the pace Moore's Law predicts for transistor count, but the main culprit seems to be disk I/O speeds.

Disk capacities have grown from megabytes to gigabytes in recent years, but disk speeds have not kept up with CPU speeds. Santo Domingo speculates that "a solid-state silicon drive or a nonmechanical optical storage device might follow Moore's Law."

Intel's recent advances in chip manufacturing technology (using Extreme Ultraviolet, or EUV, lithography) should ensure that Moore's Law itself continues to hold through at least the year 2010. But boosts in CPU transistor count and speed don't necessarily equal advancements in total system performance.