Source : Free On-Line Dictionary of Computing

Intel 486
     
         (Or "i486", "iAPX 80486", and "Intel DX4" but
        usually just "486").  A range of {Intel} {CISC}
        {microprocessors} which is part of the {Intel 80x86} family of
        processors.
     
        The 486s are very similar to their immediate predecessor, the
        {Intel 80386}DX.  The main differences are that the 486 has an
        optimised {instruction set}, has an on-chip unified
        instruction and data {cache}, an optional on-chip
        {floating-point unit} (FPU), and an enhanced {bus interface
        unit}.  These improvements yield a rough doubling in
        performance over an {Intel 80386} at the same {clock rate}.
     
        There are several suffixes and variants including:
     
        {Intel 486SX} - a 486DX with its {FPU} disabled (see
        {crippleware}).
     
        {Intel 486DX} - 486SX with a working {FPU}.
     
        486DX-2 - runs at twice the external {clock rate}.
     
        486SX-2 - runs at twice the external {clock rate}.
     
        486SL - 486DX with power conservation circuitry.
     
        486SL-NM - 486SX with power conservation circuitry; SL
        enhanced suffix, denotes a 486 with special power conservation
        circuitry similar to that in the 486SL processors.
     
        487 - 486DX with a slightly different pinout for use in 486SX
        systems.
     
        OverDrive - 486DX-2 with a slightly different pinout for use
        in 486SX systems.
     
        {RapidCAD} - 486DX in a special package with a companion {FPU}
        dummy package for use in {Intel 80386} systems.
     
        {Intel DX4}, {Cyrix} {Cy486SLC}.
     
        External {clock rates} include 16MHz, 20MHz, 25MHz, 33MHz,
        40MHz, although 16Mhz is rare now, and the 20MHz processors
        are often clock doubled.
     
        The 486 processor has been licensed or reverse engineered by
        other companies such as {IBM}, {AMD}, {Cyrix}, and {Chips &
        Technologies}.  Some are almost exact duplicates in
        specications and performance, some aren't.
     
        The successor to the 486 is the {Pentium}.
     
        (1995-02-21)