The Intel Pentium III 866 was a desktop processor with 1 core, launched in March 2000. It is part of the Pentium III lineup, using the Coppermine architecture with Slot 1. To further increase overall system performance, up to two Pentium III 866 CPUs can work together in a multi-processor (SMP) configuration. Pentium III 866 has 256 KB of L2 cache and operates at 866 MHz. Intel is making the Pentium III 866 on a 180 nm production node using 28 million transistors. The multiplier is locked on Pentium III 866, which limits its overclocking potential.
With a TDP of 27 W, the Pentium III 866 consumes only little energy. The highest officially supported memory speed is 133 MT/s, but with overclocking (and the right memory modules) you can go even higher. Actual memory technology support depends on the chosen motherboard, because the memory controller is located on the motherboard (not in the processor). Although the processor doesn't come with integrated graphics, certain motherboards with compatible chipsets can provide this capability. Inside the box you will not only find the processor, but also a Yes cooler.
Many games will refuse to start on this processor due to the lack of the SSE2/SSE3/SSE4 instruction set.