Quote:
Originally Posted by grond
The 060 can also take heavy hits in comparison to the 040 if long MUL and DIV instructions are used. It's a pity there never was an 070 with the missing instructions.
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Well Philips took a dump on the 070 name with their custom 68000 variant in the CDi. ;-)
Anyway, I think its a good idea to look at the situation from several perspectives.. Motorola CPU designers didn't just dump FPU instructions for the sake of it. The 040 was their first design to include an FPU on the same die as the CPU. It also hade significantly (for the time) increased caches compared to 030. You could say 68881/2 was over engineered feature wise :-) so it was always going to be tough to implement it 100% in this new unified design. The engineers hit some transistor budgets limits along the way and hade to make choices.. They decided to simplify the FPU (and fixed the "holes" with software patches). Remember, even with a simplified FPU this design was not great from a clock-speed perspective which became obvious with ever increasing clocks on the 486. 40MHz is all we ever got from this design. Even if they hadn't hit some transistor count limit, with full 68882 functionality, I don't exactly see it would have been clocked higher.
The 060 fixed a bunch of these issues but also had the benefit of improving manufacturing tech. Early 060 are 0,6um (or 650 nm), but last revision was almost half of that (0.32um or 320nm).
060 has about double the amount of transistors of the 040 and we got dual instruction pipeline and again much improved caches. At this point, most software using FPU had been recompiled for 040.. So 060 running 68882 code maybe was an issue only for a select few.
The fact that some old software runs poorly on 040 /060 because of the stuff that was removed is something that was known by the designers the second they decided for certain compromises, but something had to go. In the real world, we can be sure we wouldn't have had the same CPU with all characteristics intact but with all features of the 68882. If they had fully implemented FPU something else would have been compromised.
What counts in the end is the performance you get in the software you use. For me, the jump from 50MHz 030 to 50MHz 060 gave me 500% real-world performance increase so didn't exactly care what instructions they removed ;-)