The Pentium is an x86 architecture microprocessor by Intel which first shipped on March 22, 1993. It is the successor to the 486 line. The Pentium was originally to be named 80586 or i586, but the name was changed to Pentium because numbers could not be trademarked.
Major changes from the 486:
The earliest Pentiums had a clock speed of 66 MHz, with a 60 MHz version also being produced. Later on 75, 90, 120, 133, 150, 166, 200, and 233 MHz versions gradually became available. Pentium Overdrive processors were released at speeds of 63 and 83MHz as an upgrade option for older 486-class computers.
The original Pentium microprocessor had the internal code name P5, and was a pipelined in-order superscalar microprocessor. This was followed by the P54C, a compaction which was dual-processor ready. Subsequently, the P55C was released as the Pentium with MMX Technology (usually just called Pentium MMX); it was based on the P5 core, but had significant changes for MMX and improved instruction decoding.
In early 5 volt 60 MHz and 66 MHz Pentiums, a problem in the floating point unit code when doing division was discovered in 1994 and is known as the Pentium FDIV bug. These early examples of Pentium processors were also known for their fragility and relatively high levels of heat-production.
Intel has retained the Pentium brand name for later generations of processor architectures, which are internally quite different from the Pentium itself:Celeron brand is used for "value" parts (typically lower performance and lower price), and the Xeon brand is used for high-performance parts suitable for servers and power-users. The same basic microarchitecture may be used for all brands, but implementations may differ in clock speeds, cache sizes, and package and sockets. Moreover, the same name is used for chips with unrelated microarchitectures.
See also List of Intel microprocessors