Pentium II

The Pentium II brand refers to Intel's sixth-generation microarchitecture ("P6") and x86-compatible microprocessors introduced on May 7, 1997. Containing 7.5 million transistors (27.4 million in the case of the mobile Dixon with 256 KB L2 cache), the Pentium II featured an improved version of the first P6-generation core of the Pentium Pro, which contained 5.5 million transistors. However, its L2 cache subsystem was a downgrade when compared to the Pentium Pros. It is a single-core microprocessor. In 1998, Intel stratified the Pentium II family by releasing the Pentium II-based Celeron line of processors for low-end workstations and the Pentium II Xeon line for servers and high-end workstations. The Celeron was characterized by a reduced or omitted (in some cases present but disabled) on-die full-speed L2 cache and a 66 MT/s FSB. The Xeon was characterized by a range of full-speed L2 cache (from 512 KB to 2048 KB), a 100 MT/s FSB, a different physical interface (Slot 2), and support for symmetric multiprocessing. In February 1999, the Pentium II was replaced by the nearly identical Pentium III, which only added the then-new SSE instruction set. However, the older family would continue to be produced until June 2001 for desktop units, September 2001 for mobile units, and the end of 2003 for embedded devices. The Pentium II microprocessor was largely based upon the microarchitecture of its predecessor, the Pentium Pro, but with some significant improvements. Unlike previous Pentium and Pentium Pro processors, the Pentium II CPU was packaged in a slot-based module rather than a CPU socket. The processor and associated components were carried on a daughterboard similar to a typical expansion board within a plastic cartridge. A fixed or removable heatsink was carried on one side, sometimes using its own fan. This larger package was a compromise allowing Intel to separate the secondary cache from the processor while still keeping it on a closely coupled back-side bus.