Am386
An AMD 80386DX-40 in a 132-pin PQFP, soldered onboard
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| Produced | 1991 |
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| Marketed by | AMD |
| Designed by | AMD |
| Common manufacturer(s) |
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| Max. CPU clock rate | 20 MHz to 40 MHz |
| FSB speeds | 20 MHz to 40 MHz |
| Min. feature size | 1.5 µm to 0.8 µm |
| Instruction set | x86 (IA-32) |
| Microarchitecture | 80386 |
| Product code | 23936 |
| Cores | 1 |
| L1 cache | Motherboard dependent |
| L2 cache | none |
| Predecessor | Am286 |
| Successor | Am486 |
| Application | Desktop, Embedded (DE-Models) |
| Package(s) | |
The Am386 CPU is a 100%-compatible clone of the Intel 80386 design released by AMD in 1991. It sold millions of units, positioning AMD as a legitimate competitor to Intel, rather than being merely a second source for x86 CPUs (then termed 8086-family).
While the AM386 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 Intel 8086, Intel 80186 and Intel 80286 designs, and AMD's interpretation of the contract, made up in 1982, was that it covered all derivatives of them. Intel, however, claimed that the contract only covered the 80286 and prior processors and forbade AMD the right to manufacture 80386 CPUs in 1987. After a few years in the courtrooms, AMD finally won the case and the right to sell their Am386 in 1992. This also paved the way for competition in the 80386-compatible 32-bit CPU market and so lowered the cost of owning 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.
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 crucial on-chip CPU cache. However, because the Am386DX-40 had the same 32-bit width on its data bus as an 80486, but operating at the same 40 MHz rate as the processor, (rather than the 25 to 33 MHz buses of the 486 DX-2s) it had comparatively good memory and I/O performance.
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