Intel 80486
The 486DX2 66 MHz was the most widespread high-end 486 version. For many players of video games during the early and mid 1990s, towards the end of the MS-DOS gaming era, it was often coupled with 8 - 16 MB RAM and a VLB video card. This configuration was capable of running every title available for several years after its release, making it a "sweet spot" in CPU performance and longevity. The introduction of 3D graphics spelled the end of the 486's reign, because of its heavy use of floating point calculations and the need for faster cache and more memory bandwidth. Developers also began to target the Pentium almost exclusively with assembly optimizations (e.g. Quake).
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Competitive alternatives
486 compatible processors have been produced by other companies such as IBM, Texas Instruments, AMD, Cyrix, UMC, and Chips and Technologies. Some are near duplicates in terms of specifications and performance, some are not. The 486 was, however, covered by many of Intel's 386 patents as well as some of its own. Intel and IBM have broad cross-licenses of these patents, and AMD was granted rights to the relevant patents in the 1995 settlement of a lawsuit between the companies.[3]
The fastest running 486 CPU, the Am5x86, was released by AMD in 1995.
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Motherboards and buses
Early 486 machines were equipped with several ISA-slots (Industry Standard Architecture) which was noting but alternatively named 16-bit AT-bus compatible slots (plus one or two 8-bit-only PC/XT slots). Many motherboards enabled overclocking of these up from the default 6 or 8 MHz to perhaps 16.5 or 20 MHz (half the i486 bus clock) in a number of steps, often from within the BIOS setup. Especially older peripheral cards normally worked well at such speeds as they often used standard MSI chips instead of (the at the time) slower custom VLSI designs. This could give significant performance gains (such as for old video cards moved from a 386 or 286 computer, for example).
Some motherboards came equipped with a 32 bit version of the ISA-standard called EISA (Extended Industry Standard Architecture). However, EISA were rather quickly supplanted by the simpler but faster VLB (VESA Local Bus) intended for fast video cards and hard drive controllers. PCI (Peripheral Component Interconnect) then began gradually replacing VLB.
Mature 486 boards were normally equipped with both PCI- and ISA-slots, and sometimes a single VLB-slot as well. In this configuration VLB sometimes suffered performance-wise and was usually only compatible with video cards (VLB-IDE, multi I/O, or SCSI cards often had problems on motherboards with PCI slots). The VL-Bus operated at the same clock speed as the i486-bus (basically being a local 486-bus). The PCI bus also usually depended on the i486 clock but had a divider. This could be set to 1/1, but some boards limited the PCI clock to the specified maximum of 33 MHz (some network cards assumed 33MHz and would produce erroneous bit-rates in an overclocked slot). The ISA clock was either generated by a separate clock generator or by a divider of the VLB/PCI clock.
One of the earliest complete systems to use the 80486 chip was the Apricot VX FT, produced by United Kingdom hardware manufacturer Apricot Computers. Even overseas in the United States it drew attention as "The World's First 486" in a popular September 1989 issue of Byte magazine (shown right).
Later 486 boards also supported Plug-And-Play, the Microsoft technology that began as a part of Windows 95 designed to make component installation easier for consumers.
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References
- ^ Microprocessor Hall of Fame. Intel. Retrieved on 2007-08-11.
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See also
- List of Intel microprocessors
- Motorola 68040, although not compatible, often positioned as the Motorola equivalent to the Intel 80486 in terms of performance and features.
- "80486 System Architecture" published by Mindshare (pdf)
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Notes
This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
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External links
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