"mcdonaldREMOVE TO ACTUALLY REACH ME"@scs.uiuc.edu writes:
At that time (early-mid 80s), the 68000 was considered a _much_ better processor.
By Mac heads.
No. Generally. Before the mac came out. By designers, not users.
The 68k and derivatives were very popular amongst workstation makers in the early 80s (e.g., apollo, later sun, …), and was generally thought of as being a good and modern architecture — unlike the 8086.
It had far more registers, wider registers, a more regular design (so easier for compiler writers), a flat memory model, and was in many ways far more forward-thinking than the rather wacky and clunky 8086 architecture.
You have the key point exactly wrong: it was NOT forward looking. Forward looking would have meant looking for best design in a ruthlessly pipelined chip.
The 68k _did_ have many attributes that were forward thinking — larger registers, more registers, fewer dedicated registers, etc. (all of which are good for making hardware fast, and easily adapting to larger problems). It was also overly complicated in terms of things like addressing modes etc — but then, so was the 8086.
Intel’s main advantages were considered to be cost and a vague "compatibility" (heh) with earlier 8-bit intel cpus.
[Anyway, what is it about the 68k that you consider less pipeline-friendly? The 8086 with its dearth of registers and excessive use of dedicated registers seems far worse in that respect.]
It appears to be in the details rather than the overall idea. The "dearth of registers and excessive use of dedicated registers" is of course completely harmless. The Intel use of a stack floating point unit was not good for programming, but
apparently is harmless for modern chip design.
The real point is that "neatness" of instruction set is completely unimportant. The 68000 had a neat set. What matters is how well it works pipelined, which is understood only by specialists.
Sure, pipelining is important — but what is it about the 68k that makes it worse for pipelining than the 8086?
The points I mentioned _do_ actually make a difference, and it’s not in the 8086’s favor: to take advantage of pipelining you want to avoid artificial (unneeded) dependencies — and limited registers and dedicated registers _create_ artificial dependencies.
The 68k obviously had bad points too, and modern RISC designs are better in many ways; however, the 68k was at the least, better than the 8086 (which had most of the same problems, and many more).
-Miles
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