Intel 486
Intel 486
(processor)The 486s are very similar to their immediate predecessor, theIntel 80386DX. The main differences are that the 486 has anoptimised instruction set, has an on-chip unifiedinstruction and data cache, an optional on-chipfloating-point unit (FPU), and an enhanced bus interface unit. These improvements yield a rough doubling inperformance over an Intel 80386 at the same clock rate.
There are several suffixes and variants including:
Intel 486SX - a 486DX with its FPU disabled (seecrippleware).
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; SLenhanced suffix, denotes a 486 with special power conservationcircuitry similar to that in the 486SL processors.
487 - 486DX with a slightly different pinout for use in 486SXsystems.
OverDrive - 486DX-2 with a slightly different pinout for usein 486SX systems.
RapidCAD - 486DX in a special package with a companion FPUdummy 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 processorsare often clock doubled.
The 486 processor has been licensed or reverse engineered byother companies such as IBM, AMD, Cyrix, and Chips & Technologies. Some are almost exact duplicates inspecications and performance, some aren't.
The successor to the 486 is the Pentium.