AMD 5x86

The AMD 5x86 processor is an x86-compatible processor produced in the 1990s by AMD for use in 486-class computer systems. It was one of the fastest, and most universally-compatible upgrade paths for users of 486 systems.

Introduced in November 1995, the AMD 5x86 (also known as 5x86-133, Am5x86, X5-133, and sold under various 3rd-party labels such as "Turbochip") is a standard 486 processor with an internal multiplier of 4, allowing it to run at 133 MHz on systems without official support for clock-multiplied DX2 or DX4 486 processors. Like most of the later 486 parts, the 5x86 featured write-back[?] L1 cache, and unlike all but a few, a generous 16kilobytes rather than the more common 8k. A rare 150 MHz-rated part was also released by AMD.

The combination of best-in-class clock speed and the write-back cache allowed the 5x86 to equal or slightly surpass an Intel Pentium 75 MHz processor in business application performance. Also, because it was based on a pure 486 design, it was compatible with older systems, something its slightly faster rival, the Cyrix Cx5x86, had trouble with. The CPU was commonly overclocked to 160 MHz, thereby giving performance similar to that of a Pentium 100 system. Although it has been reported that individuals have successfully run the chip at 200 MHz, this would seldom have been achievable due to the rarity of video cards that could cope with the required 50 MHz system bus.

The 5x86 is also notable for the first-ever use of the controversial PR rating. Because the 5x86 was the equal of a Pentium 75 MHz processor in benchmarks, AMD later marketed the chip as "AMD X5-PR75".

AMD manufactured the 5x86 processor for ordinary PC systems until 1999. It was popular for entry-level desktop systems, apeared in many different notebook models, and also sold separately as an upgrade processor for older 486 systems. Several companies made upgrade kits which packaged an AMD 5x86 with a voltage regulator and socket converter, which allowed its use on almost any 486 motherboard ever produced.

The chip remains in production today, and is a popular choice for use in embedded controllers.

External Links

AMD's 5x86 processor page (http://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_1260_1268,00)
Picture of AMD 5x86 processor (http://www.cpushack.net/chippics/AMDAm5x86-P75.jpg) at Cpushack.net (http://www.cpushack.net)