Pentium III

The Pentium III[1] brand refers to Intel's 32-bit x86 desktop and mobile microprocessors (with the sixth-generation Intel P6 microarchitecture) introduced on February 26, 1999. The initial Katmai Pentium III contained 9.5 million transistors. The brand's initial processors were very similar to the earlier CPUs branded Pentium II. The most notable difference was the addition of the SSE instruction set (to accelerate media processing and 3D graphics), and the introduction of a controversial serial number embedded in the chip during the manufacturing process.

Similarly to the Pentium II it superseded, the Pentium III was also accompanied by the Celeron brand for lower-end CPU versions, and the Xeon for high-end (server and workstation) derivatives. The Pentium III was eventually superseded by the Pentium 4, but its Tualatin core also served as the basis for the Pentium M CPUs, which used many ideas from the Intel P6 microarchitecture. Subsequently, it was the P-M microarchitecture of Pentium M branded CPUs, and not the NetBurst found in Pentium 4 processors, that formed the basis for Intel's energy-efficient Intel Core microarchitecture of CPUs branded Core 2, Pentium Dual-Core, Celeron (Core), and Xeon.

The Pentium III was the first Intel processor to break 1 GFLOPS, with a theoretical performance of 2 GFLOPS.


Pentium III variants


Katmai

The first Pentium III variant was the Katmai (Intel product code 80525). It was very similar to the Deschutes Pentium II and used a 0.25 µm CMOS semiconductor process). The only differences were the introduction of SSE and an improved L1 cache controller, which was responsible for the minor performance improvements over the "Deschutes" Pentium IIs. It was first released at speeds of 450 and 500 MHz. Two more versions were released: 550 MHz on May 17, 1999 and 600 MHz on August 2, 1999. On September 27, 1999 Intel released the 533B and 600B running at 533 & 600 MHz respectively. The 'B' suffix indicated that it featured a 133 MHz FSB, instead of the 100 MHz FSB of previous models.

The Katmai used the same slot based design as the Pentium II but with the newer SECC2 cartridge that allowed direct CPU core contact with the heat sink. There have been some early models of the Pentium III with 450 and 500 MHz packaged in an older SECC cartridge intended for OEMs.

A notable stepping for enthusiasts was SL35D. This version of Katmai was officially rated for 450 MHz, but often contained cache chips for the 600 MHz model and thus usually was capable of running at 600 MHz.