Three - after 8086 you had 80286, 80386, 80486 and then Pentium (superscalar).
reply80186 is often forgotten to have existed because it didn't see much success in the market / because IBM skipped it and went with 80286 for the AT, but it did exist.
reply80186 Was not IBM PC compatible. It had e.g. a PIC, DMA and timer built-in, and these were incompatible with the chips in a 8086 based IBM PC.
replyThere were a few new instructions, too, mostly closing holes. You could left or right shift with a constant, while the 8086 had only 1 or the CX register. I think mul also gained a constant.
The fact that Intel released a CPU that could not be put in a PC probably indicates how low they estimated the survivability of the PC.
There were "PC compatibles" that used it, like the Tandy 2000. You are correct in that they may not have been entirely compatible, but they did exist.
replyThe 80186 didn’t really introduce anything new architecturally. It’s basically an 8086 with a few more chips bundled on-die. 80286 however introduced protected mode, expanded the address size to 24 bit, hardware enforce memory protection, multitasking, etc.
replyFour because you have to count 8086 itself (486 was one, not zero, geverations before the Pentium and so on).
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