Intel 80486 - Other Makers of 486-like CPUs

Other Makers of 486-like CPUs

486 compatible processors have been produced by other companies such as IBM, Texas Instruments, AMD, Cyrix, UMC, and SGS Thompson. Some were clones (identical at the microarchitectural level), others were clean-room implementations of the Intel instruction-set. (IBM's multiple source requirement is one of the reasons behind its x86-manufacturing since the 80286.) The 486 was, however, covered by many of Intel's patents covering new R&D as well as that of the prior 80386. Intel and IBM have broad cross-licenses of these patents, and AMD was granted rights to the relevant patents in the 1995 settlement of a lawsuit between the companies.

AMD produced several clones of the 486 using a 40 MHz bus (486DX-40, 486DX/2-80, and 486DX/4-120) which had no equivalent available from Intel, as well as a part specified for 90 MHz, using a 30 MHz external clock, that was sold only to OEMs. The fastest running 486 CPU, the Am5x86, ran at 133 MHz and was released by AMD in 1995. 150 MHz and 160 MHz parts were planned but never officially released.

Cyrix made a variety of 486-compatible processors, positioned at the cost-sensitive desktop and low-power (laptop) markets. Unlike AMD's 486 clones, the Cyrix processors were the result of clean-room reverse-engineering. Cyrix's early offerings included the 486DLC and 486SLC, two hybrid chips which plugged into 386DX or SX sockets respectively, and offered 1 KB of cache (versus 8 KB for the then-current Intel/AMD parts). Cyrix also made "real" 486 processors, which plugged into the i486's socket and offered 2 or 8 KB of cache. Clock-for-clock, the Cyrix-made chips were generally slower than their Intel/AMD equivalents, though later products with 8 KB caches were more competitive, if late to market.

The Motorola 68040 (best known for its use in the Macintosh Quadra series), while not compatible with the 486, was often positioned as the 486's equivalent in features and performance; however its performance lagged behind production 486 systems. The 486 had the ability to be clocked significantly faster without suffering from overheating problems. For a time Apple attempted to compete with Intel's clock doubling 486DX2 systems by publicizing misleading doubled clock rates for its '040-based Macintosh Performa systems, despite the lack of any clock doubling.