Intel 486 (1989 - 1994)
The 80486DX was released in 1989. It was a 32-bit processor containing 1.2 million transistors. It had the same memory capacity as the 386 (both were 32-bit) but offered twice the speed at 26.9 million instructions per second (MIPS) at 33 MHz. There are some improvements here, though, beyond just speed. The 486 was the first to have an integrated floating point unit (FPU) to replace the normally separate math coprocessor (not all flavors of the 486 had this, though). It also contained an integrated 8 KB on-die cache. This increases speed by using the instruction pipelining to predict the next instructions and then storing them in the cache. Then, when the processor needs that data, it pulls it out of the cache rather than using the necessary overhead to access the external memory. Also, the 486 came in 5 volt and 3 volt versions, allowing flexibility for desktops and laptops.
AM486DX Series (1994 - 1995) Intel was not the only manufacturer playing in the sandbox at the time. AMD put out its AM486 series in answer to Intel's counterpart. AMD released the chip in AM486DX4/75, AM486DX4/100, and AM486DX4/120 versions. It contained on-board cache, power management features, 3-volt operation and SMM mode. This made the chip fitting for mobiles in addition to desktops. The chip found its way into many 486-compatibles. AMD AM5x86 (1995) This is the chip that put AMD onto the map as official Intel competition. While I am mentioning it here on the 486 page of the history lesson, it was actually AMD's competitive response to Intel's Pentium-class processor. Users of the Intel 486 processor, in order to get Pentium-class performance, had to make use of an expensive OverDrive processor or ditch their motherboard in favor of a true Pentium board. AMD saw an opening here, and the AM5x86 was designed to offer Pentium-class performance while operating on a standard 486 motherboard.. They did this by designing the 5x86 to run at 133MHz by clock-quadrupling a 33 MHz chip. This 33 MHz bus allowed it to work on 486 boards. This speed also allowed it to support the 33 MHz PCI bus. The chip also had 16 KB on-die cache. All of this together, and the 5x86 performed better than a Pentium-75. The chip became the de facto upgrade for 486 users who did not want to ditch their 486-based PCs yet. 
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