Intel Pentium III (Katmai) microprocessor family

The first Pentium III core, Katmai, was not much different from its predecessor, Pentium II Deschutes core. Like the Deschutes-based Pentium II processors, the Katmai-based Pentium III CPUs had 512 KB back-side L2 cache running at half of the core frequency. These Pentium 3 CPUs were packaged in SECC 2 package, plugged into Slot 1 connector, used the same 0.25 micron manufacturing technology, and even had the same core voltage as Pentium IIs. As a result new Pentium 3 processors had good compatibility with old Pentium II motherboards.

The major feature of the Katmai core was SSE instruction set - 70 new SIMD instructions. These instructions were originally called KNI, or Katmai New Instructions. The SSE instructions could significantly improve performance of multimedia and graphics applications, but only if the applications were recompiled to take advantage of new instructions.

Another new "feature" of Pentium III processor was Processor Serial Number, or PSN. The PSN was unique for each Pentium III CPU, and it could be used to uniquely identify the computer. Due to privacy concerns this feature was by default disabled on many motherboards.

All CPUs with Katmai core were released during short period of time. First Pentium IIIs, running at speeds 450 and 500 MHz, were introduced in February of 1999. Just in 7 months, in September 1999, Intel released the latest and the fastest Katmai 600 MHz CPU with 133 MHz FSB.