80486

The 80486, commonly called the i486, is Intel's fourth-generation x86 microprocessor, introduced in 1989 as the successor to the 80386. It marked a major step toward a fully 32-bit, pipelined design and offered substantial performance gains over its predecessor without a dramatic increase in external clock speed.

The i486 features a 32-bit internal architecture, a five-stage pipeline, and on-chip cache memory. Most models included an integrated 8 KB level 1 cache and supported 32-bit addressing with paging for virtual memory. A floating-point unit was integrated on many DX variants, while the 486SX variant lacked an FPU, requiring a separate coprocessor if needed.

The 80486 family included several variants: 486DX, 486SX, and later 486DX2 and 486DX4. The DX models generally offered the on-chip FPU, while the SX did not. The DX2 and DX4 used clock doubling to achieve higher external bus speeds, delivering greater performance at higher clock rates. The line was manufactured over a range of process technologies and clock speeds, eventually reaching tens of millions of transistors and speeds exceeding 100 MHz in later iterations.

Impact and legacy: The 80486 quickly became the standard for personal computers in the early to mid-1990s, enabling more capable operating systems and software, including Windows 95. It remained in production alongside its successors for several years and established architectural and performance expectations that influenced later x86 designs. The i486 also spawned a broad ecosystem of compatible clones from other manufacturers.