Buffalo HDL-20W-B 386 to 486 Cx486DLC-40GP / TX486DLC/E-40GA CPU Upgrade Card
Card features either a Cyrix Cx486DLC or TX486DLC/E-40GA running at 40MHz (I have two of Cyrix-based upgrade cards, and one TX-based card). Use of this item requires era-appropriate knowledge and compatible hardware/software.