Intel Pentium 4 2.0GHz: The clock strikes two

In the nine months since its introduction, the Pentium 4 has increased in clock speed over 40%.  Today Intel is making a tremendous step forward in the eyes of the public as the first microprocessor manufacturer to offer an x86 CPU clocked at 2.0GHz.  In the eyes of the AnandTech readers, we know that today’s launch surrounds no architectural improvements to the Pentium 4 core but is more marketing than anything else. 

Over a year ago AMD beat Intel to reaching the previous highly marketable 1GHz clock speed.  While both the AMD Athlon and Intel Pentium III hit 1GHz within a matter of days of each other, only the Athlon was readily available by the end of that month.  Fast forwarding to the present day, in the same amount of time that Intel has been able to achieve a 40% increase in clock speed AMD has been able to take the Athlon from 1.2GHz to 1.4GHz, an increase of 16%.  Is the AMD Athlon inferior to the Pentium 4?

Absolutely not.  The above comparison is mainly to show you the futility of clock speed based performance comparisons.  When dealing within a particular processor family such as the Pentium 4 or the Athlon, clock speed comparisons can give you an idea of relative performance; there is no doubt that a Pentium 4 running at 1.8GHz is faster than a Pentium 4 running at 1.6GHz.  When making cross-family processor comparisons, clock speed isn’t the only way to look at the performance picture.

How much work the processor can do in a single clock cycle, measured in Instructions Per Clock (IPC), matters just as much as clock speed.  At the same time, measuring a processor’s performance in IPC wouldn’t make much sense either since a CPU capable of an average IPC of 5 instructions per clock yet only capable of running at 50MHz wouldn’t be faster than a CPU capable of an average IPC of 1.5 instructions per clock yet capable of running at 1GHz.  The combination of IPC and clock frequency determines the true performance of the CPU.

From our previous articles on the Pentium 4 architecture, we explained that the Pentium 4 is not able to perform as many instructions per clock as an Athlon.  The Pentium 4 also relies on proper usage of more elegant features such as its Trace Cache and SSE2 in order to reach peak performance levels.  Mainly the difference in IPC renders clock speed comparisons between the Pentium 4 and Athlon useless.  This ends up working as a double edged sword for AMD and Intel.  On the one hand, it allows AMD to say that their processor is faster than the Pentium 4 (on a clock for clock basis).  On the flip side however, it also brings into question whether the higher clock speeds allowed for by the Pentium 4’s architecture will allow it to eventually outperform the Athlon.  Remember, you can’t just look at IPC or clock speed; the combination of the two makes up the performance of the processor. 

If the majority of the market understood this concept then clock speed wouldn’t carry as much weight as it currently does.  Unfortunately, communities like AnandTech only make up a small percentage of the total market.  For the majority of the individuals out there that don’t have the time or the resources to research, CPU clock speed is the primary determining factor in the performance of two systems.  With the Pentium 4 now running at 2.0GHz, AMD is clearly at a disadvantage when it comes to the clock speed race.  The task upon us today however, is to find out if AMD is at a disadvantage when it comes to the performance race.