i486

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.

[2] A typical 50 MHz i486 executes 41 million instructions per second Dhrystone MIPS and SPEC integer rating of 27.9.

[1] The concept of this microprocessor generation was discussed with Pat Gelsinger and John Crawford shortly after the release of 386 processor in 1985.

[8] In fall of 1991, Intel introduced the 50 MHz i486 DX using the three layer 800 nm process CHMOS-V technology.

These low-power microprocessors have power consumption reduced by 50–75% compared to similar regular versions of these CPUs.

[12] AMD continued to create clones, releasing the first-generation Am486 chip in April 1993 with clock frequencies of 25, 33 and 40 MHz.

[12] However, these chips could not match the Intel 486 processors, having only 1 KB of cache memory and no built-in math coprocessor.

[11][12] AMD released a 133 MHz Am5x86 upgrade chip, which was essentially an improved 80486 with double the cache and a quad multiplier that also worked with the original 486DX motherboards.

[11] New computers equipped with 486 processors in discount warehouses became scarce, and an IBM spokesperson called it a "dinosaur".

[13] Even after the Pentium series of processors gained a foothold in the market, however, Intel continued to produce 486 cores for industrial embedded applications.

The combination of both CPU and FPU housed on a single die results in bus utilization rates of 50% for the 25 MHz Intel486 version.

Variants include: The maximal internal clock frequency (on Intel's versions) ranged from 16 to 100 MHz.

However, problems continued when the 486DX-50 was installed in local-bus systems due to the high bus speed, making it unpopular with mainstream consumers.

Local-bus video was considered a requirement at the time, though it remained popular with users of EISA systems.

More powerful i486 iterations such as the OverDrive and DX4 were less popular (the latter available as an OEM part only), as they came out after Intel had released the next-generation Pentium processor family.

Processors compatible with the i486 were produced by companies such as IBM, Texas Instruments, AMD, Cyrix, UMC, and STMicroelectronics (formerly SGS-Thomson).

Some were clones (identical at the microarchitectural level), others were clean room implementations of the Intel instruction set.

Cyrix made a variety of i486-compatible processors, positioned at the cost-sensitive desktop and low-power (laptop) markets.

Clock-for-clock, the Cyrix-made chips were generally slower than their Intel/AMD equivalents, though later products with 8 KB caches were more competitive, albeit late to market.

Especially older peripheral cards normally worked well at such speeds as they often used standard MSI chips instead of slower (at the time) custom VLSI designs.

However, operation beyond 8 or 10 MHz could sometimes lead to stability problems, at least in systems equipped with SCSI or sound cards.

EISA offered attractive features such as increased bandwidth, extended addressing, IRQ sharing, and card configuration through software (rather than through jumpers, DIP switches, etc.)

Some motherboards limited the PCI clock to the specified maximum of 33 MHz and certain network cards depended on this frequency for correct bit-rates.

Later i486 boards supported Plug-And-Play, a specification designed by Microsoft that began as a part of Windows 95 to make component installation easier for consumers.

Computers based on the i486 remained popular through the late 1990s, serving as low-end processors for entry-level PCs.

[23][24] Windows 2000 could run on a i486-based machine, although with a less than optimal performance, due to the minimum hardware requirement of a Pentium processor.

However, DOSBox was available for later operating systems and provides emulation of the i486 instruction set, as well as full compatibility with most DOS-based programs.

[26] The i486 was eventually overtaken by the Pentium for personal computer applications, although Intel continued production for use in embedded systems.

The 486DX2 architecture
STMicroelectronics' ST ST486DX2-40
Cyrix Cx486DRx²
The first 486 system from the UK on the cover of BYTE, September 1989