How did the Cyrix 586 chip work in an Intel 486 computer?

Solution 1:

These chips were "586" replacements that were socket/chip-set compatible with the 486. They were reworked electrically, and reduced in functionality (mostly just clock speed though) to give a "586" instruction set to a "486 platform".

The Intel ones were called "Pentium Overdrive" and the AMDs were referred to as "Am5x86". Cyrix (tech. now own by Via) also made a "Cx5x86" replacement.

In a very brief nutshell, this 'pin compatibility', and all things legal and technical that go with it, is what led Intel to decide against using "586" and start using "Pentium".

They don't maintain compatibility between brands today for many reasons, mostly market-share and legalities I would assume. :)

The idea of "Overdrive" was dropped for a couple reasons (at least).

It reduced the need for new 'whole-system' upgrades, and was actually slowing down the pace at which the 'whole-system' technologies could progress. Also, motherboard manufactures didn't like them. ;)

It was also cost-prohibitive in many cases, as you could get a whole new system without the 'old motherboard' speed/tech limitations for not much more money; especially if you kept your drives and chassis. Which, from my personal experience back in the day, was what 80-90% of (business/corp) customers did.