A compatibility card is an expansion card for computers that allows it to have hardware emulation with another device. While compatibility cards date back at least to the Apple II family, the majority of them were made for 16-bit computers, often to maintain compatibility with the IBM PC. The most popular of these were for Macintosh systems that allowed them to emulate Windows PCs via NuBus or PCI; Apple had released several such cards themselves.
12-inch PCI card with a 133MHz Cyrix 6x86 processor for the Power Macintosh 4400 and 7220
By other manufacturers
AST Research released the Mac86, a PDS expansion card for the Macintosh SE that provided DOS compatibility using a 10MHz Intel 8086. It was followed by the Mac286, which used an 80286 processor and connected to the Macintosh II through its NuBus expansion slots. After AST exited the Macintosh market, it sold the rights to both products to Orange Micro.
Orange Micro developed the OrangePC series of cards as successors to the Mac86 and Mac286. The cards used 80386, 80486, and Pentium processors, with later models featuring processors up to a 400MHz AMD K6-2. Orange Micro also released the PCfx!, a simplified OrangePC card with a soldered 200MHz Pentium processor.
Reply Corporation's DOS on Mac series of cards provided DOS compatibility through a PDS expansion card equipped with an 80486 or 5x86 processor running at up to 100MHz. They supported the Centris, Quadra, Performa, and Power Macintosh families. Later models supported PCI-based Power Macintosh computers and Pentium processors running at up to 200MHz. Radius acquired the technology in 1997 and marketed the cards under the Detente name.
In 1992, the company Aleph One released the 386PC, an expansion that added a 20 MHz 386SX processor to the Archimedes for running DOS applications. Licensed versions of these cards were soon made by Acorn for the A3020 and A4000; these official cards were available with both 386SX and 486SLC processors.
An updated DOS compatibility card with a 40 MHz 486SX (underclocked to 33 MHz) was available as an upgrade for the Archimedes' successor, the Risc PC.
The Wide-Boy64 AGB includes a system board on a cartridge providing the Nintendo 64 with full Game Boy Advance, Game Boy Color and Game Boy compatibility.