At the very core of the Pentium 4 lie the Arithmetic Logic Units (ALUs), the main integer units of the processor. Intel marketing spiced up the naming of the faster ALUs by calling them the "Rapid Execution Engine," also a fitting name for Texas. In the Pentium 4, the ALUs operate at twice the core frequency so certain instructions can be executed in half a core clock tick. In a Pentium 4 1.4GHz, the ALUs would therefore operate at 2.8GHz, and the doubling is constant at all CPU speeds. According to Intel, this will result in higher execution throughput and reduced latency of execution.

The Pentium 4 carries a form of level 1 instruction cache called a trace cache. The trace cache stores decoded micro-ops, around 12,000 of them at a time, and arranges the micro-ops into branch lines for quicker accessing. In comparison, the Pentium III data cache stores x86 instructions and does not organize them in the same way, so instructions are not loaded as quickly and they have to be decoded before execution. Trace cache contributes to keeping the Pentium 4 well fed.

The Pentium 4 also has 256k of Advanced Transfer Cache (ATC) running at the full CPU clock speed connected to the CPU core by a 256-bit data path. At 1.4GHz, this cache delivers 40GBps of bandwidth. This bandwidth will scale with CPU speed, which is tremendously important in a CPU with a high clock speed.

The Pentium 4 has 144 new instructions called Streaming SIMD Extension 2 (SSE2). This extension to MMX and SSE adds the ability to manipulate 128-bit SIMD integer arithmetic and 128-bit SIMD double precision floating point as well as adding cache and memory management operations. Software that is written to take advantage of the SSE2 extension can potentially see dramatically faster performance. Video, Speech, encryption and image processing applications will see much of their speed boosts from the Integer side of SSE2. Content creation, financial, engineering and scientific applications will see much of their speed boosts from the floating-point side of SSE2.

The negative aspect of SSE2 is that applications have to be recompiled and possibly rewritten to take advantage of the technology. Intel has had plenty of success in getting developers to adopt MMX and SSE, so we expect that most applications in the coming years will make use of SSE2.