No processor has been introduced with so much controversy surrounding its feature set and architectural changes implemented as Intel's Pentium 4. Its 20-stage deep pipeline, the SSE2 instructions and its high clockspeed all were subject to different points of view and argumentation. Although all the pros and cons of using a deep pipeline and a advanced branch prediction unit on the Pentium 4 have been scrutinized and documented by analysists and journalists alike, these features did allow Intel to push clockspeed well beyond the 1...1.2 GHz mark most processors seemed to be stuck at during its introduction.
Fig 1. Intel Pentium 4 CPU in the PGA-423 package, notice the core is mounted slightly offset from the middle.
And although AMD was quick to act upon Intel's clockspeed lead by introducing the 1.3 and 1.33GHz Athlon CPUs, Intel is simply leading in clockspeed currently, whether or not that also means they have a performance edge. The Pentium 4's SSE2 instructions were greeted with the skepticism we've also seen with the introduction of SSE, which first debuted with the Pentium III. Although many analysists and developers didn't really see much benefit from using these SIMD instructions, AMD will now also be implementing SSE in the Athlon 4, so there must be gains to be had for them to go to that length.
Quite frankly both SSE and SSE2 offer slight or large increases in performance depending on what parts of a program you choose to optimize with SIMD and whether that part is suited for optimization. Most current applications, released prior to the Pentium 4's introduction, however do not take advantage from these optimizations and as a result a Pentium 4 can be slower than expected solely by its clockspeed.
Applications and drivers however can be made to benefit from these optimizations by either recompiling them with a compiler than has SSE/SSE2 support or by releasing patches that will upgrade parts of these applications to implement SSE/SSE2 support. Good examples are the plethora of game patches that have been released and the SSE2 support in videocard drivers recently released by nVidia that offer a great boost in performance. But also Adobe and various other software developers have issued updates to their software packages that greatly increase the performance of their applications with Intel's Pentium 4.
But Intel is not out of the woods yet, although the prospective performance of its Pentium 4 begins to shine through when applications and drivers are optimized for its feature set, there's a new discussion being started. Clock throttling is a feature that is well documented in Intel documents regarding the Pentium 4's thermal requirements, however some claim that the feature is actually affecting its performance or rather making it run at half the clockspeed even if taxed a little.