page_title: Intel 80486
section_title: Other makers of 80486-like CPUs
hierarchical_section_title: Intel 80486 / Other makers of 80486-like CPUs
caption_attribution_description: English: CPU STMicroelectronics ST486DX2-40.
context_page_description: The Intel 80486, also known as the i486 or 486, is a higher performance follow-up to the Intel 80386 microprocessor. The 80486 was introduced in 1989 and was the first tightly pipelined x86 design as well as the first x86 chip to use more than a million transistors, due to a large on-chip cache and an integrated floating-point unit. It represents a fourth generation of binary compatible CPUs since the original 8086 of 1978.
  A 50 MHz 80486 executes around 40 million instructions per second on average and is able to reach 50 MIPS peak performance. Approximately twice as fast as the 80386 or 80286 per clock cycle, thanks to its five stage pipeline with all stages bound to a single cycle. The on chip enhanced FPU unit was also significantly faster than the 80387 per cycle.
context_section_description: 80486 compatible processors have been produced by other companies such as IBM, Texas Instruments, AMD, Cyrix, UMC, and SGS Thomson. 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 80486 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 80486 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 80486 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 80486-compatible processors, positioned at the cost-sensitive desktop and low-power (laptop) markets.  Unlike AMD's 80486 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" 80486 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, while not compatible with the 80486, was often positioned as the 80486's equivalent in features and performance. Clock-for-clock basis the Motorola 68040 could significantly outperform the Intel 80486 chip. However, the 80486 had the ability to be clocked significantly faster without suffering from overheating problems. The Motorola 68040 performance lagged behind the later production 80486 systems.
caption: STMicroelectronics' ST ST486DX2-40
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