Am5x86  The Am5x86 processor is an x86-compatible CPU introduced in 1995 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 Am5x86 (also known as 5x86-133, Am5x86, X5-133, and sold under various 3rd-party labels such as the Kingston Technology "Turbochip") is an Enhanced Am486 processor with an internally set multiplier of 4, allowing it to run at 133 MHz on systems without official support for clock-multiplied DX2 or DX4 486 processors. Like all Enhanced Am486, the Am5x86 featured write-back L1 cache, and unlike all but a few, a generous 16 kilobytes rather than the more common 8 KB. A rare 150 MHz-rated OEM part was also released by AMD. Since having a clock multiplier of four was not part of the original Socket 3 design (and that the 486 only have a single CLKMUL pin anyway), AMD made the 5x86 accept a 2x setting from the motherboard and instead operate at a rate of 4x. When using an Am5x86, the motherboard must be set to the 2x setting. The chip will actually physically fit into an older 486 socket such as a socket 1 or 2 or the original 168-pin 80486 socket, but doing this requires a replacement voltage regulator, since the AMD chip runs at 3.45 volts. The combination of clock speed and the relatively large 16 KB write-back L1 cache allowed the 5x86 to equal or slightly exceed an Intel Pentium 75 MHz processor in integer arithmetic in benchmarks. (Real world performance varied, however, with later Windows operating systems and many FPU-sensitive games favoring the Pentium 75 MHz.) 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 90 MHz system. It has been reported that some individuals have successfully run the chip at 200 MHz; this would require a PCI-based system (due to the instability of VLB at high speed) and uncommon motherboards and cache RAM that could cope with a 50 MHz system bus. There are four main versions of the socketed version of this CPU, manufactured in different locations.