I (vaguely) remember there being a bunch of these half-baked upgrade solutions, but are you thinking of the Cyrix 386 to 486 upgrade? http://datasheets.chipdb.

I (vaguely) remember there being a bunch of these half-baked upgrade solutions, but are you thinking of the Cyrix 386 to 486 upgrade? http://datasheets.chipdb.org/Cyrix/New%20Folder/faq386up.htm http://datasheets.chipdb.org/Cyrix/New%20Folder/faq386up.htm