The Am5x86 (also known as the 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. 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 allows the 5x86 to equal or slightly exceed an
Intel Pentium 75 MHz processor in
integer arithmetic in benchmarks. Real world performance varies, however, with later Windows operating systems and many FPU-sensitive games favoring the Pentium 75 MHz. Because it is based on a pure 486 design, it is compatible with older systems, something its slightly faster rival, the
Cyrix Cx5x86, has trouble with. The CPU is commonly
overclocked to 160 MHz, thereby giving performance similar to that of a Pentium 90 MHz system. There are four main versions of the socketed version of this CPU, manufactured in different locations. There is the common ADW variety, as well as the later ADY, ADZ and BGC. The later models were the preferred versions of the chip, because they were rated for higher temperatures and thus more forgiving of overclocking. The Am5x86 made the first-ever use of the controversial
PR rating. Because the 5x86 is the equal of a Pentium 75 MHz processor in benchmarks, AMD later marketed the chip as "Am5x86-P75". Sales of the Am5x86 were an important source of revenue for AMD at a time when lengthy delays in bringing the
AMD K5 to production were threatening the company's profitability. AMD manufactured the Am5x86 processor for ordinary PC systems until 1999. It was popular for entry-level desktop systems, appeared in many different notebook models, and also sold separately as an upgrade processor for older 486 systems. Several companies made upgrade kits with an AMD 5x86 with a voltage regulator and socket converter, which allows its use on virtually every socketed 486 motherboard ever produced. Several companies also provided upgrades for older 486 notebooks by replacing soldered 486 CPUs. The chips were even used on later
Acorn RiscPC "PC card" second processors. The RiscPC's
OpenBus memory interface was only 32 bit, which meant that the
Pentium could not be easily interfaced to it. Intel's expensive
Pentium Overdrive for 486 systems is a troublesome CPU, with many compatibility issues, and so is not used. The 5x86 therefore provided the acme of RiscPC Windows performance. The chip remained in production for a long time, as it was a popular choice for use in
embedded controllers. One derivative of the 5x86 family is the core used in the
AMD Élan SC520 family of
SoC 00200microcontrollers marketed by AMD. This powers the original
Cisco PIX 501 model. AMD Am5x86-P75 (cropped).jpg|An Am5x86-P75 model ADZ Ic-photo-AMD--Am5x86-P75-(Am486DX5-133W16BGC)-(486-CPU).jpg|A late Am5x86-P75 for Socket 3, model W16BGC Kl AMD Am5x86-P75 PQFP.jpg|Surface-mounted Am5x86-P75, model V16BHC AMD Am5x86 die.JPG|AMD Am5x86 die shot AMD Elan SC520-133AC.jpg|
AMD Élan SC520
system on a chip based on the Am5x86 core == Models ==