Author: David Franklin
Date: 08:29:59 06/15/00
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On June 15, 2000 at 02:34:59, Mogens Larsen wrote: >On June 14, 2000 at 22:10:17, David Franklin wrote: > >>Why *shouldn't* it start at 1.4Ghz? There are always tradeoffs to be made; one >>possible tradeoff is to accept a low number of instructions/clock, if that >>allows you to have a very high clock rate. > >Basically there's no problem starting at 1.4GHz, but that would probably mean >too expensive for the ordinary consumer. Again, I have to ask you *why* 1.4Ghz == expensive? There's no real reason to assume that. In general Intel's high end consumer chip (i.e. non-Xeon) always costs about $1K; if Williamette was clocked at 200Mhz (but was still Intel's highest performer), I bet they'd still charge the same price as if it was clocked at 2Ghz. Only thing likely to change that is competition from AMD. >Is the current Pentium unable to reach the clock rate we're talking about? Or is >the gain just too small in performance/speed ratio? By all accounts, 1Ghz is very near the ceiling for the P6 architecture in 0.18 micron. But who really knows outside of Intel? > >>Of course, it seems Intel have gone a *long* way down that route with Willamette >>- some parts are actually double pumped (effectively 2.8Ghz), but the tradeoff >>is a *really* deep pipeline, and pretty high latencies for a lot of >>instructions. It doesn't look like a winning strategy to me, but only time will >>tell. > >Can you explain what double pumping is in layman terms? Simple - some bits use both the rising and falling edges of the clock, so you get 2 'ticks' per clock cycle. It seems like Intel have basically tried to take the 'maximum clock rate' to a new extreme (2.8Ghz), at the expense of having many instructions take a lot more than one clock tick. If you can get all the pipelining to work, you should be able to get spectacular performance, but if you can't, a 20+ deep pipeline is going to hurt. *Bad*.
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