Several companies—mainly AMD and Cyrix—have developed processors that are compatible with Intel processors. These chips are fully Intel compatible, so they emulate every processor instruction in the Intel chips.

Many of the chips are also pin compatible, which means that they can be used in any system designed to accept an Intel processor; others require a custom motherboard design.

Any hardware or software that works on Intel-based PCs will work on PCs made with these third-party CPU chips. A number of companies currently offer Intel-compatible chips, and some of the most popular ones are discussed here.

AMD Processors

Advanced Micro Devices (AMD) has become a major player in the Pentium-compatible chip market with its own line of Intel-compatible processors. AMD ran into trouble with Intel several years ago because its 486-clone chips used actual Intel microcode.

These differences have been settled, and AMD now has a cross-license agreement with Intel. In 1996, AMD finalized a deal to absorb NexGen, another maker of Intel-compatible CPUs. NexGen had been working on a chip it called the Nx686, which was renamed the K6 and introduced by AMD. AMD refined the design in the form of the K6-2 and K6-3.

Its more recent chips, called the Athlon XP and Duron, are designed similarly to the Pentium III/4 and Celeron that have used both a similar but not identical slot and socket design.

The newer AMD Athlon and Duron processors as well as the Athlon XP are designed to use Socket A, also called Socket 462. The newest AMD processor, the Athlon 64, is the first 64-bit processor designed for desktop computers. It uses the new Socket 754.

Cyrix

Cyrix was purchased by National Semiconductor in November 1997 and by VIA Technologies in 1999. Prior to that, it had been a fabless company, meaning it had no chip-manufacturing capability.

All the Cyrix chips were manufactured for Cyrix first by Texas Instruments and then mainly by IBM up through the end of 1998. Starting in 1999, National Semiconductor took over manufacturing of the Cyrix processors. More recently, National has been purchased by VIA Technologies.

All Cyrix chips were manufactured by other companies such as IBM (who also marketed some of the 6x86 chips under its own name), National Semiconductor, and now VIA Technologies.