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One of the comments I read about the new Mac (and it's soon(?) forthcoming bigger brethren/sisters), is that it is so fast because it can actually issue 8 instructions per cycle, which goes against conventional wisdom that you top out max IPC in the 3 to 4 region. The crux here was that RISC was making a comeback as the complexity of x86/CISC decoding was rising exponentially and as such going further than decoding 4 instructions per cycles was Unobtainium for Intel/AMD. Correct me if I understood it wrong. What I find much more interesting is that Mill Computing are throwing the rulebook about IPC out the window and are aiming way higher at their IPC numbers. They do a lot of stuff to make that happen, both for actual decode and for handling parallellism. |
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Also don't forget that theoretical IPC is a maximum. In reality it often drops to a mere 1 because of dependencies. For me that A1 chip is taking the path IBM Power took before - optimize to death and ultimately fail because the advantages of RISC don't work anymore. That doesn't mean ARM won't take over the market - but the reason will not be raw cpu speed. Quote:
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If you do 8 per clock but have to execute 18, you're slower than if you execute 4 per clock and need only 6. |
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Whether that proves or disproves anything I don't know. |
The only sure thing is that another cpu war has begun. Only time will tell how it ends.
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The bad thing about the Apple chip is that only Apple has it and most probably Apple will keep it to themselves. Other ARM processors aren't likely to kill off x86 any time soon. And Apple isn't going to eliminate x86-based Windows PCs either.
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We can also dream a little. For example, it was quite possible that a cheap Amiga based on the 68040 might have been released in 1994 or 1995. |
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The 68060 was released in late 1994 when Commodore was already gone, so there wasn't much else they could have done to 'provide some ground' for it. However they did produce an 040 board for the A4000 which they could easily have modified to take an 060. If Commodore had survived for a few more years I'm betting they would have produced one. |
There is a strange race condition on the 68060 as in "you cannot restore the CPU state in all conditions". Typically, you want a debugger to be able to save the CPU state, fiddle around with its registers, and then restore the state back to how it was before.
Interestingly, this is not always possible on the 68060, which is really a bizarre exception throughout the motorola series. The condition is as follows: If the FPU is in NULL state, and a non-implemented floating point exception is taken because the first opcode the FPU ever sees is something it does not handle in hardware, then the FPU is still in NULL state, but the FPIAR register points to the instruction to be emulated (has to, actually, as the FPSP code needs to grab and interpret the instruction from there). However, this FPU state cannot be restored. Either, you can place a value back into the FPIAR, but this results in the FPU being in IDLE state, not in NULL state. Or you place the FPU back in NULL state, but then the next read from FPIAR returns 0, not the faulting instruction. This is different from the 68040 - a non-implemented FPU instruction there creates a rather lenghtly exception stack frame and the proper address in FPIAR, and both can be restored. In reality, it does not matter too much whether the FPU is in IDLE or in NULL state, though. For the 68060, the stack frame is the same size anyhow. |
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In the particular use case, this is not an option. But it does not matter too much, it was rather an observation and a curiousity than a problem statement. |
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