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Saying there has been no change at all since 1985 is exaggarating...

The step from 386 to 486 wasn't big. There were a few new instructions, increase in clocking speed, and the ability to run the CPU at higher clocking speeds than the memory bus.

The step from 486 to Pentium wasn't that great either. More instructions (MMX) and a superscalar architecture (i.e. two pipelines).

Pentium Pro, however, was something else. P6 is internally a RISC processor, while previous ones are CISC. The microprogramming allows one to use CISC instructions, although they are executed as a series of RISC instructions internally. Out-of-order execution, longer pipelines.

Yes, it is fully backwards compatible, but this was also quite a feat if you look at the design.

From Pentium Pro to Pentium II was only a small step. Pentium II is essentially Pentium Pro with more (and in some models, slower) cache and a bit faster 16-bit execution mode.

And Pentium III wasn't that big either. Faster cache, SSE instructions.

However, if you look at Pentium 4, you'll see some big differences again. It's essentially a completely new CPU (using the (controversial) Netburst architecture) that just happens to be compatible with previous x86 CPUs.

Source: Wikipedia.

(Yes, I'm aware of other CPU manufacturers. However, the development in other camps is very similar to how it happened at Intel.)

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