The Pentium II is a sixth-generation x86 architecture microprocessor by Intel, introduced on May 7, 1997. It was based on a modifed version of the P6 core first used for the Pentium Pro, but with improved 16-bit performance and the addition of the MMX instructions which had already been introduced on the Pentium MMX.
Unlike previous Intel processors such as the Pentium and Pentium Pro, the Pentium II was packaged in a slot-based form-factor rather than a socket one. This larger package was a compromise allowing Intel to separate the secondary cache from the processor while still keeping it on a closely coupled bus. This separate cache was slower (running at half the processor speed) than that in the Pentium Pro, but solved the Pentium Pro's low yields allowing Intel to introduce the Pentium II at a mainstream price level.
A low-end version of the Pentium II - essentially a Pentium II with less (or no) level 2 cache - was marketed under the name "Celeron". The Pentium II Xeon was a high-end version intended for use on servers.
By early 1999, the Pentium III superseded the Pentium II.
Remarked Pentium IIsPentium II at Wikipedia