I486

The i486 (also known as the 80486) is a 32-bitmicroprocessor introduced by Intel in 1989 as the fourth generation of the x86 processor family. It builds on the i386 architecture with pipelined instruction execution and on-chip cache while maintaining binary compatibility with software for earlier x86 processors.

It was the first tightly-pipelinedx86 design as well as the first x86 chip to include more than one million transistors. It offered a large on-chip cache and an integrated floating-point unit. When it was announced, the initial performance was originally published between 15 and 20 VAX MIPS, between 37,000 and 49,000 dhrystones per second, and between 6.1 and 8.2 double-precision megawhetstones per second for both 25 and 33 MHz version. A typical 50 MHz i486 executes 41 million instructions per second Dhrystone MIPS and SPEC integer rating of 27.9. It is approximately twice as fast as the i386 or i286 per clock cycle. The i486's improved performance is thanks to its five-stage pipeline with all stages bound to a single cycle. The enhanced FPU unit on the chip was significantly faster than the i387 FPU per cycle. The i387 FPU was a separate, optional math coprocessor installed in a motherboard socket alongside the i386.

The i486 was succeeded as the series flagship by the original Pentium (also known as the "586") in 1993 while the Celeron took over as the low-end series in 1998. Orders were discontinued for the i486 on March 30, 2007, and the last shipments were on September 28, 2007.