The Pentium Pro is a sixth-generation x86 architecture microprocessor (P6 core) produced by Intel and was originally intended to replace the original Pentium in a full range of applications, but later, was reduced to a more narrow role as a server and high-end desktop chip. The Pentium Pro was capable of both dual- and quad-processor configurations. It was introduced in an unusually large, rectangular Socket 8 form factor in November 1995. Intel has since discontinued it in favor of the newer high-end Xeon processor lines.
The Pentium Pro (given the Intel product code 80521), was the first generation of the P6 architecture, which would carry Intel well into the next decade. The design would scale from its initial 150 MHz start, all the way up to 1.4 GHz with the "Tualatin" Pentium III. The Pentium Pro had a theoretical performance of 400 MFLOPS.  The core's various traits would continue after that in the derivative core called "Banias" in Pentium M and Intel Core (Yonah), which itself would evolve into Core architecture (Core 2 processor) in 2006 and onward.
Pentium Pro clock speeds were 150, 166, 180 or 200 MHz with a 60 or 66 MHz external bus clock. Some users chose to overclock their Pentium Pro chips, with the 200 MHz version often being run at 233 MHz, and the 150 MHz version often being run at 166 MHz. The chip was popular in symmetric multiprocessing configurations, with dual and quad SMP server and workstation setups being commonplace.
The Pentium Pro was succeeded by the Pentium II, which was essentially a cost-reduced and re-branded Pentium Pro with the addition of MMX and enhanced 16-bit code performance. Costs were reduced by using standard SRAM cache chips running at half-speed, which increased production yields.
Eventually a 333 MHz Pentium II Overdrive processor for Socket 8 was produced by Intel as an upgrade option for owners of Pentium Pro systems, which had 512 KiB of high speed cache. However it only supported dual-processor operation, which did not make it a usable upgrade for high end quad-processor systems.
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