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From: izot@f171.n221.z1.FIDONET.ORG (Geoffrey Welsh)
Newsgroups: comp.sys.cbm
Subject: Re: C128,C128D, and C128C??? Questions
Message-ID: <1892.242832FB@isishq.FIDONET.ORG>
Date: 22 Mar 89 13:40:52 GMT
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 > From: leblanc@eecg.toronto.edu (Marcel LeBlanc)
 > Message-ID: <89Mar20.194245est.2737@godzilla.eecg.toronto.edu>
 
 > I'm not sure of exactly what it is you're trying to say, but it looks like
 > you're equating MHz on 8502 with MHz on Z80, which is completely false.  A
 > 2Mhz 6502 is (almost) 4 times faster than a 2Mhz Z80.  This is because
 > memory (or IO) accesses on a Z80 take 3-4 cycles, whereas the same
 > operation
 > on a 6502 takes only one cycle (yes, the 6502 was an early RISC :-) ).  So
 > even if you could get the Z80 to run flat out at 4MHz, it would still be
 > only a little more than half the speed of the 8502 at 2MHz.
 
   Marcel, you miss the points that (a) the circuitry in the machine existed 
to allow the 8502 to run 2 MHz in 40-column as well as 80-column mode, without 
blanking the screen; (b) failing that, the circuitry existed in the machine to 
make the Z80 run 4 MHz at all times (in stead of 2 cycles on, 2 off) when the 
40-column screen was disabled.
 
   Geoff ( watmath!isishq!izot )
 


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