Am386

The Am386 CPU was released by AMD in 1991. A 100%-compatible clone of the Intel 80386 design, it sold millions of units and positioned AMD as a legitimate competitor to Intel, rather than just a second source for "x86" CPUs (then termed "8086-family").

While the CPU was essentially ready to be released prior to 1991, Intel kept it tied up in court. AMD had previously been a second-source manufacturer of Intel's designs, and AMD's interpretation of the contract was that it covered all of them. Intel, however, claimed that the contract only covered the 80286 and prior processors. After a few years in the courtrooms, AMD finally won the case and the right to sell their Am386. This paved the way for competition also in the market for 8086-compatible 32-bit processors and lowered the cost of buying a PC.

While Intel's 386 design peaked at 33 MHz, AMD released a 40 MHz version of both its 386DX and 386SX, extending the lifespan of the architecture. The AMD 386DX-40 was popular with small manufacturers of PC clones and with budget-minded computer enthusiasts because it offered near-80486 performance at a much lower price than a real 486.

The 386DX-40 could match or even slightly outperform a 486SX-25 in popular benchmarks and many real-world applications, while costing less. Integer performance at 40 MHz thus approached that of low-end 486 CPUs, but rarely exceeded it. This is because the 486 needed fewer clock cycles per instruction, thanks to its tighter pipelining (more overlapping of internal processing) in combination with a crucical on-chip CPU cache. However, because the Am386DX-40 had the same 32-bit width on its data bus as an 80486, it had good memory and I/O performance even compared to many 486s.

Floating point performance could be boosted with the addition of an inexpensive 80387 coprocessor, although performance would still not approach that of the on-chip FPU of the 486DX. This made the Am386DX a suboptimal choice for scientific applications and CAD using floating point intensive calculations. However, both were niche markets in the early 1990s and the chip sold well, first as a mid-range contender, and then as a budget chip. Although motherboards using the older 386 CPUs often had limited memory expansion possibilties and therefore struggled under Windows 95's memory requirements, boards using the Am386 was sold well into the mid-1990s; at the end as budget motherboards for those who were only interested in running MS-DOS or Windows 3.1x applications. The Am386 and its low-power successors were also popular choices for embedded systems, for a much longer period than their life span as PC processors.

External links

* [http://www.amd.com/epd/processors/6.32bitproc/10.am386fami/ AMD.com: Am386 Family 32-bit Processors]
* [http://www.cpu-collection.de/?l0=co&l1=AMD&l2=386%20DX cpu-collection.de: Pictures]
* [http://www.digital-daily.com/editorial/amd-history/index02.htm AMD: 30 Years of Pursuing the Leader. Part 2]